It seems for those viewers who have a background in electronics or not and do have a love of guitar tube amps, will not find a better place to learn than from you! I have searched the web and I can't find any other channel that provides a more easy practical way of explaining and showing the incredible world of tube amps. There are others who do share good info on tube amps, but not like you. Not only the teaching but Rusty and Jack provide the all important human-pet aspect. We love you! Thankz
+Audio Tech Labs Wow....Thanks so much, ATL. Rusty, Jack, and I really appreciate your kind and generous assessment of our work. Extra nice comments like this make it all worthwhile :)
Uncle Doug I think your whole channel should be archived in the national library. You are a beautiful human-being. Thank you for sharing your knowledge. (and YES Rusty is included!!)
I would like to point something out that I don't see commented on very often; the amount of work required to produce a clear, concise and informative video. It's not easy! After watching Uncle Doug's videos I thought I would make a video and post my first amp build and I have been greatly surprised at how much effort is required to do it correctly. Lighting, camera angles and maintaining continuity has been a hell of it's own. I find myself getting caught up in the build and remembering several steps later that I forgot to turn on the camera, so I check the lighting, camera settings, etc. and try again. Other times I notice repetition in my explanation of a specific step, in which case I stop and do it over and over,and then try to pick up the build again where I left off. I have even documented some incorrect steps that I have had to delete or replace with something else. Keeping continuity is not as easy as it looks, and I think this may be the reason I see so many demos on YT of the finished product and not very many good videos of the build. Uncle Doug makes this look easy and it's not. Another great video.I feel like I'm in a classroom.
+Slugg0matic Thanks so much, Randy. You're completely correct.....it's hard as heck to come up with a smooth, coherent video, especially when you're performing distracting, hazardous technical tasks at the same time. This video consisted of at least 100 separate snippets (selected from about 250 that were made) which were all joined together....while maintaining (reasonable) lighting and verbal continuity. As you found out, this can be a real handful. Even after making 124 of them, it's still a challenge that can take a full day or two. Thanks for mentioning this.....it was very thoughtful and perceptive.
+Uncle Doug man, I hate to put you on the spot...but your wisdom is inspirational! I don't mean just in these technical videos but as a human. Such generosity and civility. And these traits appear to have an influence on your viewers. You're doing Great Work--thanks!
Wow, thanks so much, JR. I really appreciate your very kind sentiments and hope that I can live up to them. You're quite right about our viewers....they tend to be the most civil, kind, generous, and appreciative that you will ever see on any Internet site. It's an honor to associate with them, and you.
+Slugg0matic .......................You are so right.....I've followed this Channel very carefully.........there is much to be learned here...much more than the operation of a tube amp..... I consider this a peerless instruction ...on instruction....That is Uncle Doug's and Rusty's ............. Bailiwick ......only one other person was as good as UNK.....Robert Persig...." Zen and the Art of Motorcycle Maintenance"........ who tries to explain........."explaining"......and the idea of explaining.....and all it of it's magical subtleties....it's all about "Quality ".........( I write the manuals you read.....) Hah! Yep....He makes it look way way too easy.......Hah ha ha... a gift.....
This guy is the real deal. I wish he lived closer to me as i love learning and i love vintage vehicles !! I forgot about the kitties and the dog. As i believe they understand more than we realize they know they have it made. Keep up the great work!
Hi Uncle Doug & Rusty, I reviewed the Resistors Part 2: Power and Wattage Requirements, Ohm's Law. Looks like I have a little math to do, no problem, I love math. I have no problem taking your word for anything amp related, your a living legend on RUclips to any one that is into amps. You can't beat the voice of years of experience. Thankyou so much for all that you share for those who need to know the correct and proper way of things. I hope your all having a great summer. Take care, C.
Thanks from Spain! When I studied electronics, tubes was obsolete! Now, I'm repairing and building tube guitar amps, and love to learn from awesome teacher like you. Thanks again!
Very clear explanation of Ohms law related to amplifiers. I think everybody has to know this basic calculations when building or troubleshooting an amp. Thanks!
I cannot tell you how much you have helped me understand tube amplifiers and increased my general electrical understanding! I have been reading books, websites, etc for weeks on amplifiers only to have been able to name parts and maybe what they do but not understand it. After an hour or 2 of your videos I actually get it! You rock!
I've been repairing amplifiers and effects (attempting and occasionally succeeding) for myself and friends for a while now, mostly through trial and error/things I've picked up along the way. Finding your channel has really opened me up to how circuits work. I've been taking notes and applying things I've learned from you, and I gotta say, I'm very thankful for the videos you make!
Rusty & Jack displayed Ohms of resistance by turning down Georgette and the drone, respectively. As always, an extremely interesting and scintillating presentation. Thanks, Doug.
awesome series! Like most of your tutorial videos, I get more out of them the 2nd time I watch.. my M.O. has been to watch it 1x, learn just enough to be extremely dangerous, tackle the subject, get zapped, burn up at least a few components & finish by letting all the smoke out of the wires. Then, upon re-watching the videos, it doesn't seem like chinese arithmetic & a lot of things become relateable & understandable. I built myself a cooking 5f6a 1x12 combo & I've had to figure out how to assemble it, wire it & troubleshoot some 60hz hum & tweak it into shape. it is an awesome amplifier, probably the best I've ever played thru. it largely was made possible off the education I've learned here.. As always, Thanks UD!..
THANK YOU again for taking the time to make this series. This is making up for all the classes I slept through back in my teenage years. I actually get it now. Jack seems to enjoy the drone.
+Greg's Garage You're welcome, Greg. I'm glad to hear that the videos are helpful. Jack is usually much more aggressive toward the drone, without actually touching it. I got him up from his daily nap to make the video and he was still a little sleepy.
Great video Uncle Doug! Nothing like using the actual readings from a working amp to get "real world" understanding of what's going on. A lot of useful info provided. A nice follow up to your previous video. Can't help but love the practicality of those old Valco amps.
+skeeterbuck Thanks, Skeeter....glad you liked it. I agree completely that visual learning is way more effective than auditory. The screen current issue was unrelated to the topic, but it was a great opportunity to cover a rather elusive subject. Yes, Valco amp design and function are about as good as it gets. I've been appreciating (and collecting) them for several years.
Jack seems both fascinated and totally annoyed by the flying drone. xD Thanks again Uncle Doug for helping me put practical use and relearning of my high school electronics. Now in middle life, I am revisiting my youthful aspirations to understand and practically apply electronics knowledge into my passion for music.
Great video, as usual! Thanks Uncle Doug! Glad to see the two laggards are finally "off the dime" and back to work! I have that same type of volume control knob on my 1958 Gretsch Electromatic guitar! Love that "G!"
+Tim Dockery You're welcome, Tim. Yes, I had to get Jack up from his daily nap to participate in the video, hence his rather passive (sleepy) performance. I believe the Gretsch knobs are identical on the guitar and amp.....solid, heavy, and knurled.
Poor Rusty...”Other dogs in the neighborhood don’t have to deal with these weird tests! Arfff!!” I’m learning too much. These really are great videos! I can actually follow what the Guitologist is doing in HIS videos much better now,too.
Thank you uncle Doug, Rusty and Jack for the excellent series of videos on tube amps and other related things. So far, I have not come across any such informative and we'll explained videos such as yours. I just wanted to add something to your explanation on power. Firstly, we measure energy in Joules and power in Watts. Watt is an alternative name to the original unit of measure, which is Joules per second (J/S), named after the scientist, James Watt. As you can see, power is simply the energy consumption rate or how many Joules consumed per second. As an example, a 100W electric bulb consumes 100Joules of energy (electrical) during each second of its operation. Unfortunately, we cannot possibly covert all that electrical energy to light energy. For example, maybe 90% of that energy would be converted to light energy while 10% maybe lost as heat energy. Considering the topic of resistors, for example a 1W resistor is capable of safety dissipating heat energy up to 1 Joule during each second of its operation. Assuming that all the electrical energy in this resistor is converted to heat energy, we could calculate the maximum current through this resistor using the formula I=√(Power/Resistance). If the resistance is 1 Ohm, then the maximum current would be 1A. If resistance is 100 Ohm then the maximum current handling capability would be √(1/100) = 0.1A, without burning the resistor. Cheers and looking forward to seeing more interesting videos from Uncle Doug and his team.
+Patrick Greisberg Thanks, Patrick, and as a fan of both M.P. and the 3 S, I appreciate the flattering comparisons. It's not always easy being the straight man/stooge to a 17 year-old cookie-stealing dog, but I guess I finally found my niche in life :)))
Excellent tutorial Uncle Doug. That amp is very clean looking. I'm restoring an old cc 1980's slave power amp (solid state not valve) and internally it was a right old mess. Full of dust, fluff and rusty terminals. I'll release a video of still photo's when it's complete - I'm completely refurbishing it with new components. I also discovered that you can use the wife's nail varnish remover to clean the PCB tracks of flux residue, although don't try this on the screen printed side as the component markings are removed..
+Andy Wragg Thanks, Andy.....glad you liked the video and the old Gretsch amp. I thought that all you true ampoholics would get a kick out of it. Let me know when you post your video. Rusty and I would love to watch it.....as long as there is no choice between it and a dog cookie :)
I doubt that anything could interfere with my "daily habits", Andy, but I do find that chewing the cookie before swallowing does make the day-after much more enjoyable :))
+Audio Saurus Thanks, AS. He's old but still quite energetic and agile, unless the video camera is aimed at him, and then he becomes the old, lazy dog we all know and love :)
Quite helpful. I've been shown how to connect for bias measurements, but I like seeing it on the schematic better. Much better in my brain than before.
Hi Doug! I just started watching this series and I'm glad I did. I've browsed your videos for quite a while but always skipped this resistor series thinking it was going to be too basic. But I'm now adding it to my playlist of tube amp working principle :) Btw, seeing your gorgeous 6150, it must be the exact same amp as my little Supro Super 1606b. Even the speaker looks identical.
Thanks for your thumbs-up on our Resistor videos, Eric. Yes, Valco made many virtually identical amps under different names.....Gretsch, Supro, National, Oahu, etc.
You are a great teacher! Thank you for these videos. Im batting around taking some electrical engineering classes. It has always fascinated me. And I love math lol! Just got my first tube amp and I want to know how it works.
Would have loved to have you as my teacher! Just starting to learn about tube amps and I enjoy the way you show how things work. Bonus , I have a black cat which is a clone of yours! Looking forward to all your videos. Leo, Montreal, CANADA
Thanks so much, Leo. It would have been wonderful to have a classroom full of all our great viewers.....can you imagine the jam sessions that could have happened :) More are coming, so stay tuned :)
Hi Doug, thanks for the great video! I'm now going to work just before the weekend, starting with a big smile on my face:) This amp is an great condition. Is it really 50 years old? Unbelievable!
+R HEIDEMAN Thanks, RH. Since we're both getting a wee bit old, Rusty and I now see eye-to-eye on what really matters in life. Jack is generally more aggressive toward the little drone, but, as usual, once the camera is on, the drama suddenly ends.
Uncle Doug, once again you have concisely yet thoroughly explained a difficult subject. (It is not surprising to discover you were an algebra teacher; much respect sir!) Here's a question about resistor wattage in the context of longevity: do higher wattage resistors tend to drift less over time, and does it depend on the material? For example: an amplifier from 1971 has a 15k 1/4 watt resistor in the tone stack, 100k 1 watt plate resistor, (both carbon based,) and 1k 5 watt ceramic resistor in the power supply. If one were to test the values of all three, assuming they were within 5 - 10% tolerance when the amp was built, which, if any, would remain closest to its original value 45 years later? (Assuming, of course, that the amplifier was all original and in good condition.) Thank you once again for sharing your knowledge!
You're welcome, Michael, and thanks for your nice comments. It's hard to predict exactly how resistors will hold up over time. A lot depends on the current they face, which varies widely throughout the circuit. I would guess that the old fashioned carbon comp resistors would be the worst, and modern metal film resistors would be the best. In between are the carbon film resistors that many of us use. I would think that higher wattage resistors would be more stable than low-wattage (especially puny 1/4W....which I never use) simply due to the larger mass for heat dissipation.
I stay every day looking if you put something new video in your channel. That's like a food for my brain and my soul. "I'm addicted on Uncle Doug Channel" Master, do you have some other site to view these schematics beyond the "Old Frets"? Thank for share a piece of your life and time with us!
+Humberto Martins Ferreira Junior Thanks so much, Humberto. In some cases, like the Supro Tremo-Verb, I post the schematics on my own site and provide links in the video. I guess I could start doing this more often. Thanks for watching and for the suggestion.
Hi Uncle Doug. After scouring the internet for better understanding of how tube amps work, your videos have really helped me clear the fog. I have a "learning handicap" in the sense that I find it difficult to assume things and move on without actually understanding how things exactly work, the purpose of each component etc. Your videos have been a cut above the rest, in that, you do not assume that the viewer has prior working knowledge or that something is too obvious to explain. You actually explain the function of every component. I really appreciate this. Thanks for your efforts. In the schematic you show, I have two questions 1. In the first input stage there is no cathode resistor. Can the circuit still work satisfactorily? As I understood from your other videos, the cathode resistor serves to put it at a more positive voltage compared to the grid for biasing purposes. Here both grid and cathode are effectively grounded. 2. What is the purpose of the capacitor on the primary winding of the transformer connected to mains supply. It looks like a filter cap but why would I need to smooth out the input AC voltage? Thanks again for your time.
1. There's more than 1 way to bias a vacuum tube- "grid bias" works equally well. 2. The capacitor on the AC line is there to filter out noise coming in on the power line.
Hello Doug. Another very well done how to video. So well done I could even understand how to do it. And that's saying a lot ! Very happy to see Rusty and Jack in the video. Jack could be Molly's twin no kidding. Thank you again and much respect Doug. All my very best. Oh and looking forward to your next video in this series. Bobby
Great videos! I like them alot. I had a thought about drawing the B+ from pin 8 of the rectifier. It matters if you ever intend to use a solid-state plug-in rectifier instead of valve rectifiers. I hade my amp wired to take the B+ from pin 2, which was all fine. Then I plugged in an octal socket solid-state rectifier I had bought. The new rectifiers cathodes were only wired to pin 2 causing my amp to draw all the amps current through the 5V filament winding. Which might be bad, I don't know. But drawing B+ from pin 8 seems to be standard in most circuits you see.
6:56 Stock as a what? I haven't heard that expression before. Googled around, but I must admit my ignorance. You've set yourself up for an excellent mini-series here, Uncle Doug. You could highlight just about any aspect of amplifier circuits, layout do's and don'ts, capacitance, inductance, etc. You're booked right up until we put you in a home--or they put ME in one... Another delightful video, suitable for repeated clobberings over my head for retention. My highest compliments again. And that Gretsch is certainly NSFW. Nice. Ironic, really. I have had nothing but fear and dread toward all Algebra teachers to date.
+JC Haywire Greetings and thanks, JC. "Stock as a stone" is an old saying we used way back (1960's) when drag racing our hot rods on the backstreets of town. It implied that an engine and running gear were completely original, which (unlike my video usage) was almost always a lie.....especially if money was going to be wagered on the outcome. I've been touching lightly on all the topics you mentioned, but now intend to go into a bit more depth, which will require an infusion of math. Hopefully, the approach I take will overcome old fear and loathing.
+Cawfee Dawg You're welcome, CD. Generally, his fur sticks up all over and he jumps around like a lunatic, challenging the drone, but (naturally) the moment I brought out the camera, he became a passive observer rather than the wild cat we all know and love :)
Really Interesting video! A few questions came to mind as I watched it: 1) Why doesn't the cathode on the first 12ax7 have a resistor? 2) What is the purpose of the .001 coupling capacitor that bypasses the volume pot on the way to the grid of v2? Does this mean that the volume can never by completely shut off since some of the amplified AC signal from v1 always gets to the grid of v2? 3) Why does v2 have a larger resister (270k) on its anode DC power than v1 (100k)? P.S. Rusty and Jack need a patreon page so folks like us that appreciate their hard work can upgrade their treats and toys! Thanks for the great instruction. -Gerald
1.) By reducing (in this case to zero) the cathode bias resistance, plate current and gain are maximized. Circuit designers have all sorts of reasons for selecting component values, and sometimes their choices are hard to explain. 2.) A capacitor that bypasses a volume pot is to allow high frequencies to get past the pot resistance unabated.....i.e. it enhances high frequency. 3.) Both anodes are within V1, Gerald. Plate resistance is used to control the output of an amplification stage. In this circuit, V1a has lower plate resistance (100K) and lower output than V1b (270K). Apparently the circuit designer felt that using lower output from V1a to drive V1b produced better tone. Rusty and Jack do have a Patreon page, Gerald. If you watch some of our more recent videos, a link is provided. Thanks for watching and commenting.
on 2) Does this mean that you can hear the high frequencies while playing even with the volume turned all the way down? It seems like it would, but I'm kinda surprised an amp designer would do that if so. on 3) Yeah, I realized that I should have said something like V1a, V1b vs V1, V2
2) No, since the VC resistance is to ground, once the VC is turned to zero, all signal goes to ground. However, once the VC is increased, treble frequencies will be able to avoid the resistance of the VC pot and will be accentuated.
The first half of the 12AX7 is 'grid leak biased'. The few electrons which hit the grid develop a negative voltage at the grid across the high value 6.8M resistor which is enough to bias the tube.
Power : Defined as when one’s wife threatens to divorce you because your spending too much time working on amplifier circuits. Boy iam going to miss her!!! Hahaha 😂 Glad im not married!! Thanks Uncle Doug your videos are so intriguing that Iam now fully engrossed in learning all about tube electronics despite having an Associate Degree in Electronics Technology that i earned back in 1995. We learned so much solid state theory then but sadly, didnt learn repair techniques much then back in the early ninetees. We were more focused on design and the ciriculum was designed to transfer to a 4 year program or gain entry level employment in the field. . I distinctly remember that we built a 50 watt push pull transistor amp that was powered by a low powered sony walkman hihi.. and that was the extent of amplifier design projects we were involved in then. Sometimes we just memorized information and regurgitated it until it became habit and kept on chugging along just to cover all the information in the semester. Your style and instruction is superb and i understand everything you show us. Tubes are so much more interesting and rewarding in my opinion to learn and will always retain a niche use in amplifiers and communications applications in the electronics field. Thanks so much for all of this instruction iam really enjoying this series and learning alot :)
I'm glad to hear that you have come to prefer tube circuitry, Tahoe. To me, SS vs Tube is like a photograph vs a Rembrandt painting. Both serve a similar purpose, but the latter elevates the subject matter to a much higher level. Thanks for joining us.
Well done as always. Rusty's choice went the way I thought, but love seemed to slow him down a bit. :)) Jack looked to be thinking up all the four letter words a cat might know. :)) Andrew
+bullthrush Rusty did seem to give the portrait of his girlfriend a little smooch....before grabbing the cookie and running off to the bowels of the workshop to wolf it down :) Jack is normally more aggressive toward the drone, but in the video he came off as an innocent victim....probably trying to elicit sympathy (and more cat treats) :)
I love the clarity of your presentations. I notice that you almost never stumble over your words, using um or uh to fill the gaps. I wonder if you read from a script (doesn't sound like it) or if you were a teacher in your career?
Another amazing and incredibly informative video! A request: not sure if you've done this in the past catalogued in another video, but could you make a video on your method of properly discharging capacitors when working on an amp? There seem to be many methods out there, but I have a feeling I'd like to follow your way. Many thanks! -Alex
+Alex Perez Thanks so much, Alex. I have demonstrated the method in the How to Bias videos. I use a 100 Ohm 10W resistor. One lead is grounded and the other is touched to each positive filter cap lug for several seconds to ensure full discharge. You can then double check each lug with a DC voltmeter just to be sure. Best of luck :)
Thanks a 6150 eh? That sounds like the Grand dad of the 5150, lol jk. I really enjoy your teaching & thank you for sharing this knowledge. This is like a great way to relax listening to a real american man that is NOT the numb skulls they make men out to be on TV. You are a Gem Uncle Doug. Gods Bless you & yours.
+Donald Filbert Yes, indeed, and he is usually much more aggressive toward it, in a thoroughly comical way. I interrupted his nap to make the video, so he was still a little sleepy and passive.
Uncle Doug, you're videos are the best! Pass some love onto the furry ones too, plz. At 20:37 you show the circuit requiring .564W to pass thru that resistor (dam)... And you then say double it for safety. Did you not say earlier in this series how that would be like throwing a hotdog down a hallway? How the high wattage resistor would have little affect on the lower flow through the "dam"? I've learned so much from these videos, so thank you so much. But I'm baffled on this one, perhaps you could clarify in the future? 🙏☯️
I don't recall the hot dog analogy, but whenever you calculate the wattage requirement for a resistor it is standard practice to at least double the wattage for safety purposes.
Like the way you explain all this doug, your videos have been an invaluable resource for understanding these concepts in an easier way. Question? : How is it that you are showing on the schematic that the power going into the tube is coming from the (Cathode pin 8) ground leg? I guess you are just measuring the voltage across the 1 watt (330?) resistor ? Please clarify, Im not seeing this right. Thanks --
Thanks, Vin. The electrons which form the plate current all come from the grounded centertap of the high voltage winding of the power transformer, through the chassis to the cathode of the tube, then flow from the cathode past the grid to the plate. There are various ways to measure the plate current. Please see my videos that explain them.
My Hewlett Packard HP48 will let me plug in numbers and it has Ohms Law & Power built into an equation library. It has the RC RL RCL circuits and phase angle changes in voltage and current, reactance, reluctance, impedance, resonant frequency, inductance, etc. etc.
Your pets have made two interesting observations - perceived female fickleness (poodle) and applied aerodynamics (quad 'copter). Great lesson Doug. You mentioned 'Ballast Resistor' at the beginning but not as an application - later perhaps ?
Thanks, Dave. I'm not sure about your ballast resistor question. I use the term to refer to high wattage resistors that are used to reduce voltage by converting it to heat.
Both our video production and drone flying have taken a back seat lately to hot rod building, Q. Hopefully, we will get back into both previous hobbies before long.
Super Nice applications for Amp Analysis.....using the lesson. Works better in my head. ps: the Director, Actor, LIghting, Writing guys that work for your Videos are really good.....(they may want to know about paypal's tip jar)----they are that good! KaChing!
Uncle Doug! Did you take a bite out of the doggy biscuit bofore giving it to rusty? Food for thaught. I think your vids Are very informative Educational and done with excellence Thanks.
Hi Uncle Doug, another great video, thanks. I have a question related to resistors, I am planning to scratch build a Fender AB764 amp from parts found at garage sales but am a little confused regarding potentiometer selection. The schematic I have only specifies values needed but not type (A or B). Does it matter or is it important to use the right type for volume, tone etc. Any guidance would be very much appreciated.
+Tony H If you're wondering about Audio (Log) Taper vs Linear Taper, I suggest using Audio for tone purposes.....volume, treble, midrange, bass,etc. and Linear for purely electrical purposes, i.e. variable bias control, etc.
Thank you Doug.In this video you use the term "voltage drop". Is this always the voltage measured across a resistor and that term is "voltage drop"? So the voltage drop is the number you use in the many calculations where "V" is a factor? The term "voltage drop" is not to be confused with any other voltages like the 6.3 filament or 5vac.These are set voltages. I think I get it now. Thank you
+Tom Ward I understand your initial confusion, Tom. The term "voltage" can be a static (or "set") term, i.e. to describe the output of a battery or power transformer winding, i.e. a 6V battery.....or it can be a dynamic term, as in "voltage drop" which reflects the amount of current flowing through a resistor, and the different voltages available on either side of the resistor. Voltage drop only exists when current is flowing through the circuit, and it is the value to use in any formula that includes "I" or current (i.e. Ohm's Law).
Volts are used as the units of measure of two different but related quantities. Potential, a.k.a. 'voltage' is the amount of 'electromotive force' (e.m.f.) available to force a current (electrons) to pass through a resistance. Potential difference (p.d.) a.k.a. 'voltage drop' is the difference in potential (voltage) between any two points in a circuit, e.g. the two ends of a resistor. If we have a 6V battery, we can decide that the negative terminal is at 0V, which means that there will be a voltage (e.m.f.) of +6V at the positive terminal. If we connect a resistor between the terminals, one end of the resistor is at a voltage of +6V and at the other end is at a voltage of 0V so there is a voltage drop (p.d.) of 6 - 0 = 6V across the resistor. If we replace the single resistor with two equal value resistors in series, the voltage (e.m.f.) at their junction is +3V, so there is a voltage drop of 6 - 3 = 3V across one resistor and a voltage drop of 3 - 0 = 3V across the other.
Another brilliant video, thanks. Do you have one that works backwards - how to calculate expected voltages and currents/power in a valve circuit without having the actual circuit built i.e. I want to build an amp but do not know voltages apart from the HT or wattages for each resistor???
Ohm's Law works both ways, Dave, but to calculate a value for either Voltage, Current, Resistance, or Power......you need to know two of the values in order to calculate the third. So to determine the Current, you would have to know the Voltage and Resistance, and so forth.
@@UncleDoug Ah ok, thats where it gets tricky - I guess on an amp i would start at the pre-amp end and use the published tube current and voltage plus the series of dropper/filter resistors to gusstimate resistor wattage etc?? I'll have to play with some diagrams I think
Very good demonstration Uncle Doug. I found it interesting on the Resister wattage. Now I have some 2 watt 270k & 470k ohm resisters I have been using in filter Cap usage. All seems to be ok so far. Now this is over kill I'm sure but could it lead to an issue? In my schematic some of the 270k ohm resisters have 10% wrote by the resistance value.
+Douglas Gilliland That's a great idea, Doug. Sometimes I go back to old videos and have to chuckle over his antics. Maybe a "Best of" anthology would be a hit.
Hello uncle Doug. I am new to ohms law and finding it facanating. Q. in the cathode bias resistor,356 ohms. why would you ground/earth it as shown in the schematic? I conceed that I have missed some thing fundamental here. Great video.
+neddypong Greetings and thanks, NP. Cathode bias resistors always have one end connected to ground. Ground is the source of electrons for the cathode and the voltage drop that provides the net negative grid bias.
Uncle Doug, amazing video as always! :) When you're measuring the resistance in-circuit, aren't you actually measuring the resistance in parallel with the whole circuit?
+Olivil Thanks so much, Olivil. In the case of the measurements I took, I don't believe this is the case. Looking at the schematic, the cathode bias resistor and OPT primary are isolated from the circuit and thus not in parallel with any other resistance.
Hey Doug. I noticed on this example you measure plate voltage from plate pin 3 to pin 8 cathode instead of from plate to ground when using the cathode resistor method.. They are the same i guess. If there is a difference please let me know and if it does not matter I'll just use either way. Thanks
In grid-biased circuits, PV is measured from plate to ground. In cathode-biased circuits, PV is measured from plate to cathode (which has a higher charge than ground).
In my school (portugal) they taught volts as U instead of E (E is for energy in joule, J), so it took me a little while to understand some equations. Is it one of those US and EU preferences/disagreements in notation? Also, when you taught/teach physics how do you teach your students the notation? Thanks for the videos!
Very good Doug! Theoretically wasn't Rusty's "first contact" with the photo of his lady-friend? ;) So how does an Algebra Instructor become so versed in electronics?
+Tony Manns You're right, Tony. Maybe I misinterpreted his reaction, and love did win out after all :) My hobby (and eventual business) of restoring vintage jukeboxes in the 1980's required the ability to repair their amplifiers, speakers, mechanisms, wiring, and complex electronic components. Through experience and independent study, I developed the necessary skills to perform all aspects (other than chrome or nickle plating) of a full restoration myself. This same knowledge and skill, combined with additional experience and extensive independent study, allows me to do the same with guitar amplifiers.
Hi Doug :) Thank you for this Video and all the other informative and well done work...Have to say.. Anode Current and Cathode Current Minus Screen Current, Very interesting and begs the question....with regard to Tube Matching....Would it be possible to Build a Tube matching device other that a tube tester for matching output tubes..? Also,,Can you do a Video on Tube testing...Triodes preamp tubes and power tubes..Thanks Doug.. Terence.
+Terence Kaye You're welcome, Terence. The primary source of variance between output tubes is the amount of current they conduct, which is largely based on the age and condition of the cathode. As tubes age, their current capabilities diminish, their bias gets "cooler", and they begin to sound rather "dead". Tube matching, in my experience, is simply grouping tubes with similar current conduction. Any device that could power up the tubes (heaters, screen, and high voltage) and measure current conduction would work. I simply use the amplifier itself.....insert different output tubes, and measure the plate current of each, selecting two that are quite close in value. Tube testing would not be a particularly riveting video topic. You plug in a tube, set the dials, push a button, and get an emission reading......and the specifics of the process differ greatly from tube tester to tube tester (so the video would only relate to the tester used) ......but this is not how tubes are matched. Tubes with similar emission values may have very different plate current readings.
+Uncle Doug Hi Doug.. Thank you...It's amazing just how complicated Tube matching can sound given the many different angles....Thank you once again Doug,,,,you truly are a wonderful source of inspiration...Will have to show you the Guitar amplifier I've just completed.....And I have an Idea for a Tube matching set up as well....This could get interesting.. LOL....
You're welcome, Terence. You can post photos of your amp on my Facebook page: Uncle Doug's Vintage Amps. Before you start designing all sorts of tube matching devices, recall that any amp can be used for this purpose, simply by inserting tubes and measuring their plate current.
Hi, Uncle Doug! I’m from Brazil and I want to design my own guitar amps. I have some questions: When one could say that a circuit is an original design? This Gretsch 6150 has a very similar circuit to the 5F1 Fender Champ. It is a clone or an original design? Your channel is a gold mine! Thanks for everything!
Greetings, Rodrigo. In my opinion, there are no "original" tube circuit designs. Way back in the 30's and 40's, RCA engineers designed virtually all the tube circuits imaginable, and every amp since then has used most, if not all, of the circuitry they designed.....so both the 6150 and the Champ are actually derived from their earlier work
Hello Doug, in a double ended PP EL84 Class AB amp with a 300V B+ into pin 9, 295V out of the plates@ pin 7 and bias resistor of 130 Ohm from pin 3 (which also includes a 25 uF cap), the power rating of the resistor I have seen is 10W. This seems high. Is there a reason for this. Perhaps because there are two power tubes?
+allanpennington If the tubes share the bias resistor, then the wattage would be doubled, and (like horsepower and money), bigger (wattage) is way better than not enough. It would be helpful to know the voltage drop across the cathode bias resistor. The bypass cap would have virtually no effect on the plate current.
Another newbie question for you Doug. At 8:43, is it possible to determine plate current just from looking at the schematic? I am looking at a schematic and I have the plate and cathode resistor values and the B+ voltage at the transformer, but not the voltage drop across the plate resistor. It's a 12AU7 tube. Any tip on how to figure that out?
Not that I'm aware of, Joel. There is really no accurate way to predict the plate current without taking measurements during normal operating conditions. One main variable is the tube itself.......they all tend to vary in PC levels.
I wish i didn't have to ask questions Doug but i'm not the sharpest knife in the drawer. I guess if its grid bias you can't use the cathode resistor method since the cathode is grounded and you could go from pin 3 to pin 8 of the 6V6 or you have to use the OT measurements to determine voltage and bias with a fixed bias amp. I was just curious about cathode bias and getting plate voltage from pin 3 to pin 8 and if pin 8 and ground were at both the same potential in a cathode bias amp If you think my questions are silly or tedious i'll get the hint if you just don't want to respond. I was good with measuring voltage at the plate by measuring pin 3 to ground and then i saw you use pin 8 instead of ground and was wondering if that was just for fixed bias or cathode bias as well? I keep watching your videos since they are fantastic and it troubles me i can't figure it out without having to worry you about it since you probably already gave the answer. Thanks
In cathode bias, you can measure the voltage drop across the cathode bias resistor to determine gross PC. PV is measured from plate to cathode. In grid bias, you measure the voltage drop across the OPT winding(s) to find PC. PV is measured from plate to ground.
May I asked a Question? I have a 50 watt 6v6 powered amp. it's push pull, I've removed the two outter tubes , one died on me. So I though it would be nice to cut down the power on this one is that Dangerous? In my understanding it is not. Also what other power tube could be exchanged for the 6v6's? Thanks
+Watchman4u I am guessing that the amp had four 6V6 output tubes and you removed two of them. You have to be careful which two you pull. If the amp still works and sounds OK, then I guess you were lucky. There are Internet sites that discuss this issue. You might want to do a Google search and read up on it. Since you have pulled two 6V6's, your power transformer could probably handle a pair of 6L6GB's or 5881's without going up in smoke. You should check the tube bias.....they will probably be rather "cold" otherwise.
Uncle Doug Yes 4 Power Tubes I pulled the outer ones. Yikes I thought it could be either or two inside or the two out side. Thx I didn't know that I've read about people using 6L6's in just Two sockets of four of 6v6 amp, to compensate for the power difference, I'd like to get a EL34 sound . I never own one the 6L6 Fender Twin is what I used for years w/a ss amp in stereo live. Then I got the 5150 w/2 4x12's wow Loud never had it past 4 1/2 ever on stage I played @ 3 with the soundmen going nutz screaming please turn down. Thats a Monster Amp & 16 ohm speakers 100Watt they don't break up easy a Clean amp sound Good thru them 5150 Cabs Sheffield speakers. I wish I could mod the thing to get a cleaner clean oh & Tank w/springs.lol Maybe they left that off because the amp moves you the Ev's coming outta the speakers would blow my pants leg. Sound pressure I see guys Crank them things w/Distortion in front of it. Insane. Too much. I did some good blues recording SRV Clapton Jimi sound w/Almond Bro's in there a guys amp blowed up during tracking in my studio so we used the 5150 till we could over dub with his amp when he got it fixed it sounded so good like an Hot rodded Fender Twin I need to get those tracks & share em. Thats a great player in Athens Ga. Gifted young man. Thanks for the advice never mind the rambling I love this stuff I don't like Hi Tech.lol
+Watchman4u I believe you did the right thing, although a schematic would be necessary to be sure.....the two outer or the two inner are usually the ones to pull. Since the pairs are wired in parallel, you only want to pull one from each pair so you still have push-pull alternation. Pulling both tubes from one parallel pair would not be good. As I said, I believe you could get away with two 6L6's as long as they are the only output tubes in place.
How practical is it to rewire a dual 6973 output over to EL84 ? I'll wait on your very very professional answer with baited breath. Thank you very much. Love your videos. Say hi to the crew for me thanks.
It seems for those viewers who have a background in electronics or not and do have a love of guitar tube amps, will not find a better place to learn than from you! I have searched the web and I can't find any other channel that provides a more easy practical way of explaining and showing the incredible world of tube amps. There are others who do share good info on tube amps, but not like you. Not only the teaching but Rusty and Jack provide the all important human-pet aspect. We love you! Thankz
+Audio Tech Labs Wow....Thanks so much, ATL. Rusty, Jack, and I really appreciate your kind and generous assessment of our work. Extra nice comments like this make it all worthwhile :)
+Audio Tech Labs Yes I've been spreading Uncle Dougs Knowledge Vault of the Tube Grimoire chn on real Tube Amps. :)
Thanks, W4.....we appreciate any advertising and support :)
Uncle Doug I love that bit where Rusty looks @ his girl friend the toy then picks the food. lol Thats about right as you said. lol Good stuff.
He actually licked the photo....a "kiss" I guess.....and then grabbed the cookie and ran.
Uncle Doug I think your whole channel should be archived in the national library. You are a beautiful human-being. Thank you for sharing your knowledge. (and YES Rusty is included!!)
+iguisard You're welcome, Ig. Rusty and I are quite flattered by your kind comments. Thanks for watching :)
I would like to point something out that I don't see commented on very often; the amount of work required to produce a clear, concise and informative video. It's not easy!
After watching Uncle Doug's videos I thought I would make a video and post my first amp build and I have been greatly surprised at how much effort is required to do it correctly. Lighting, camera angles and maintaining continuity has been a hell of it's own.
I find myself getting caught up in the build and remembering several steps later that I forgot to turn on the camera, so I check the lighting, camera settings, etc. and try again. Other times I notice repetition in my explanation of a specific step, in which case I stop and do it over and over,and then try to pick up the build again where I left off. I have even documented some incorrect steps that I have had to delete or replace with something else. Keeping continuity is not as easy as it looks, and I think this may be the reason I see so many demos on YT of the finished product and not very many good videos of the build.
Uncle Doug makes this look easy and it's not.
Another great video.I feel like I'm in a classroom.
+Slugg0matic Thanks so much, Randy. You're completely correct.....it's hard as heck to come up with a smooth, coherent video, especially when you're performing distracting, hazardous technical tasks at the same time. This video consisted of at least 100 separate snippets (selected from about 250 that were made) which were all joined together....while maintaining (reasonable) lighting and verbal continuity. As you found out, this can be a real handful. Even after making 124 of them, it's still a challenge that can take a full day or two. Thanks for mentioning this.....it was very thoughtful and perceptive.
+Uncle Doug man, I hate to put you on the spot...but your wisdom is inspirational! I don't mean just in these technical videos but as a human. Such generosity and civility. And these traits appear to have an influence on your viewers. You're doing Great Work--thanks!
Wow, thanks so much, JR. I really appreciate your very kind sentiments and hope that I can live up to them. You're quite right about our viewers....they tend to be the most civil, kind, generous, and appreciative that you will ever see on any Internet site. It's an honor to associate with them, and you.
+Slugg0matic .......................You are so right.....I've followed this Channel very carefully.........there is much to be learned here...much more than the operation of a tube amp..... I consider this a peerless instruction ...on instruction....That is Uncle Doug's and Rusty's ............. Bailiwick ......only one other person was as good as UNK.....Robert Persig...." Zen and the Art of Motorcycle Maintenance"........ who tries to explain........."explaining"......and the idea of explaining.....and all it of it's magical subtleties....it's all about "Quality ".........( I write the manuals you read.....) Hah!
Yep....He makes it look way way too easy.......Hah ha ha... a gift.....
Thanks, Bill. Rusty and I really appreciate it :)
This guy is the real deal. I wish he lived closer to me as i love learning and i love vintage vehicles !! I forgot about the kitties and the dog. As i believe they understand more than we realize they know they have it made. Keep up the great work!
Thanks so much, AG. We appreciate the kind words, and so do our furry family members.
Hi Uncle Doug & Rusty, I reviewed the Resistors Part 2: Power and Wattage Requirements, Ohm's Law. Looks like I have a little math to do, no problem, I love math. I have no problem taking your word for anything amp related, your a living legend on RUclips to any one that is into amps. You can't beat the voice of years of experience. Thankyou so much for all that you share for those who need to know the correct and proper way of things. I hope your all having a great summer. Take care, C.
You're welcome, Cass, and thanks so much for your very nice comments. Rusty and I sincerely appreciate them and wish you the very best.
Thanks from Spain! When I studied electronics, tubes was obsolete! Now, I'm repairing and building tube guitar amps, and love to learn from awesome teacher like you.
Thanks again!
You're welcome.....and thanks for the nice comment. Best of luck with your new tube amp hobby.
Very clear explanation of Ohms law related to amplifiers. I think everybody has to know this basic calculations when building or troubleshooting an amp. Thanks!
+Marco Hermans You're welcome, Marco. I agree that we must master the basics before we can move on in sophistication. Glad you enjoy the videos :)
I cannot tell you how much you have helped me understand tube amplifiers and increased my general electrical understanding! I have been reading books, websites, etc for weeks on amplifiers only to have been able to name parts and maybe what they do but not understand it. After an hour or 2 of your videos I actually get it! You rock!
That's great news, SR, and exactly why Rusty, Jack, and I create our videos. Best wishes for your continued pursuit of knowledge.
I've been repairing amplifiers and effects (attempting and occasionally succeeding) for myself and friends for a while now, mostly through trial and error/things I've picked up along the way. Finding your channel has really opened me up to how circuits work. I've been taking notes and applying things I've learned from you, and I gotta say, I'm very thankful for the videos you make!
You're quite welcome, Dillon. Keep watching, studying, and learning.....and best of luck with the development of your repair skills :)
Rusty & Jack displayed Ohms of resistance by turning down Georgette and the drone, respectively. As always, an extremely interesting and scintillating presentation. Thanks, Doug.
+Nancy Daniels You're welcome, ND.....glad you liked it :)
awesome series! Like most of your tutorial videos, I get more out of them the 2nd time I watch.. my M.O. has been to watch it 1x, learn just enough to be extremely dangerous, tackle the subject, get zapped, burn up at least a few components & finish by letting all the smoke out of the wires. Then, upon re-watching the videos, it doesn't seem like chinese arithmetic & a lot of things become relateable & understandable. I built myself a cooking 5f6a 1x12 combo & I've had to figure out how to assemble it, wire it & troubleshoot some 60hz hum & tweak it into shape. it is an awesome amplifier, probably the best I've ever played thru. it largely was made possible off the education I've learned here.. As always, Thanks UD!..
Thanks for sharing, Jon. It's great to know that the videos are helpful and informative.
You are absolutely awesome. Your impact as a human being is being felt by many. Thank you!
Wow.....thanks so much, VA.
THANK YOU again for taking the time to make this series. This is making up for all the classes I slept through back in my teenage years. I actually get it now. Jack seems to enjoy the drone.
+Greg's Garage You're welcome, Greg. I'm glad to hear that the videos are helpful. Jack is usually much more aggressive toward the drone, without actually touching it. I got him up from his daily nap to make the video and he was still a little sleepy.
Great video Uncle Doug! Nothing like using the actual readings from a working amp to get "real world" understanding of what's going on. A lot of useful info provided. A nice follow up to your previous video. Can't help but love the practicality of those old Valco amps.
+skeeterbuck Thanks, Skeeter....glad you liked it. I agree completely that visual learning is way more effective than auditory. The screen current issue was unrelated to the topic, but it was a great opportunity to cover a rather elusive subject. Yes, Valco amp design and function are about as good as it gets. I've been appreciating (and collecting) them for several years.
Jack seems both fascinated and totally annoyed by the flying drone. xD Thanks again Uncle Doug for helping me put practical use and relearning of my high school electronics. Now in middle life, I am revisiting my youthful aspirations to understand and practically apply electronics knowledge into my passion for music.
We're glad the videos are informative, Chris. Good luck with your continuing education.
Great video, as usual! Thanks Uncle Doug! Glad to see the two laggards are finally "off the dime" and back to work! I have that same type of volume control knob on my 1958 Gretsch Electromatic guitar! Love that "G!"
+Tim Dockery You're welcome, Tim. Yes, I had to get Jack up from his daily nap to participate in the video, hence his rather passive (sleepy) performance. I believe the Gretsch knobs are identical on the guitar and amp.....solid, heavy, and knurled.
Poor Rusty...”Other dogs in the neighborhood don’t have to deal with these weird tests! Arfff!!” I’m learning too much. These really are great videos! I can actually follow what the Guitologist is doing in HIS videos much better now,too.
Thanks, William. Glad the videos ae helpful.
Great fundamental material and presentation. Lots of clarity.....
I always like your sharing of some of your personal life.
Thanks, Paull. Glad you enjoyed it.
I love it! As we get older, food is the only thing that really matters! My wife would vouch for that!
They say that food really is the most basic necessity.....especially Popeye's Chicken ;)
Uncle Doug is an excellent instructor.
Thanks, Robert.
Thank you uncle Doug, Rusty and Jack for the excellent series of videos on tube amps and other related things. So far, I have not come across any such informative and we'll explained videos such as yours. I just wanted to add something to your explanation on power. Firstly, we measure energy in Joules and power in Watts. Watt is an alternative name to the original unit of measure, which is Joules per second (J/S), named after the scientist, James Watt. As you can see, power is simply the energy consumption rate or how many Joules consumed per second. As an example, a 100W electric bulb consumes 100Joules of energy (electrical) during each second of its operation. Unfortunately, we cannot possibly covert all that electrical energy to light energy. For example, maybe 90% of that energy would be converted to light energy while 10% maybe lost as heat energy. Considering the topic of resistors, for example a 1W resistor is capable of safety dissipating heat energy up to 1 Joule during each second of its operation. Assuming that all the electrical energy in this resistor is converted to heat energy, we could calculate the maximum current through this resistor using the formula I=√(Power/Resistance). If the resistance is 1 Ohm, then the maximum current would be 1A. If resistance is 100 Ohm then the maximum current handling capability would be √(1/100) = 0.1A, without burning the resistor.
Cheers and looking forward to seeing more interesting videos from Uncle Doug and his team.
You're welcome, Hashara, and thank you for your very detailed and well-written comment. It is both clear and quite informative.
Another great video Doug. I learned a lot. Thanks for taking the time to make this and post it.
+Michael Streets You're welcome, Michael. I'm glad the video was helpful.
I'm loving these videos, your teaching style is superb! You're telling us what's going on without talking over our heads.
On to #3
Thanks, Shy. I'm glad the videos are easy to understand.
And good Jack, he resisted attacking the drone!
I must be a supernerd. I love your shows. Very informative and a certain 3 stooges meets monty python vibe. I'm glad Rusty is still helping out.
+Patrick Greisberg Thanks, Patrick, and as a fan of both M.P. and the 3 S, I appreciate the flattering comparisons. It's not always easy being the straight man/stooge to a 17 year-old cookie-stealing dog, but I guess I finally found my niche in life :)))
Great two part video! Very helpful and enlightening. Thank you!
+redfishbum You're welcome, Bart. Glad you liked the videos. Part 3 was just posted. :)
straight to the point!!! excellent videos uncle Doug, thanks a lot
+jeff b You're welcome, Jeff....glad you like them :)
I love this channel !! Thank You!!
You're quite welcome, Rodrigo. Thanks !!!!!
Thanks again, Uncle Doug! Great job, as always!
+achdee55 Thanks, Arch. Glad you liked it :)
Excellent tutorial Uncle Doug. That amp is very clean looking. I'm restoring an old cc 1980's slave power amp (solid state not valve) and internally it was a right old mess. Full of dust, fluff and rusty terminals. I'll release a video of still photo's when it's complete - I'm completely refurbishing it with new components. I also discovered that you can use the wife's nail varnish remover to clean the PCB tracks of flux residue, although don't try this on the screen printed side as the component markings are removed..
+Andy Wragg Thanks, Andy.....glad you liked the video and the old Gretsch amp. I thought that all you true ampoholics would get a kick out of it. Let me know when you post your video. Rusty and I would love to watch it.....as long as there is no choice between it and a dog cookie :)
Go easy on the dog cookies Uncle Doug, I hear they can play havoc with your regularity.
I doubt that anything could interfere with my "daily habits", Andy, but I do find that chewing the cookie before swallowing does make the day-after much more enjoyable :))
I'm glad to see that Rusty is doing fine.
+Audio Saurus Thanks, AS. He's old but still quite energetic and agile, unless the video camera is aimed at him, and then he becomes the old, lazy dog we all know and love :)
Very productive and informative! Thanks for sharing your knowledge sir!
+Randy Schartiger You're welcome, Randy. Glad you liked it :)
again, very well explained Uncle Doug. i'm getting addicted to this serie 😉. oh.. can i say, Rusty made the best choice.
+BAMPSANDPEDALS Thanks so much, B&P. Glad you enjoy the videos. Yes, Rusty and I share his preference :)
+BAMPSANDPEDALS I was only surprised at how long it took him to chose the cookie !!! ;) ;)
+Donald Filbert yeah... and i think Uncle Doug even had to edit the video because it took so long. A great dog, isn't he? ☺
He is indeed, B&P, and you're right, I did edit out a few seconds :)
Quite helpful. I've been shown how to connect for bias measurements, but I like seeing it on the schematic better. Much better in my brain than before.
+DeadKoby That's what we're here for, DK :) It's great to hear that the video was helpful. Thanks for watching.
Legend! So good, so useful and to the point! Many thanks and keep 'em coming!
+carvingbone Thanks, CB.....glad you liked it :)
Hi Doug! I just started watching this series and I'm glad I did. I've browsed your videos for quite a while but always skipped this resistor series thinking it was going to be too basic. But I'm now adding it to my playlist of tube amp working principle :)
Btw, seeing your gorgeous 6150, it must be the exact same amp as my little Supro Super 1606b. Even the speaker looks identical.
Thanks for your thumbs-up on our Resistor videos, Eric. Yes, Valco made many virtually identical amps under different names.....Gretsch, Supro, National, Oahu, etc.
You are a great teacher! Thank you for these videos. Im batting around taking some electrical engineering classes. It has always fascinated me. And I love math lol! Just got my first tube amp and I want to know how it works.
Thanks, Jacob. You can gain a good grasp of tube electronics just from studying the videos on YT and some sites such as robrobinette.com/Amp_Stuff.htm
For each collection of videos, itd be awesoem if you had the links to the others in the description! love ur videos
Thanks for the nice comment and helpful suggestion, DL.
Would have loved to have you as my teacher! Just starting to learn about tube amps and I enjoy the way you show how things work. Bonus , I have a black cat which is a clone of yours! Looking forward to all your videos. Leo, Montreal, CANADA
Thanks so much, Leo. It would have been wonderful to have a classroom full of all our great viewers.....can you imagine the jam sessions that could have happened :) More are coming, so stay tuned :)
Hi Doug,
thanks for the great video! I'm now going to work just before the weekend, starting with a big smile on my face:)
This amp is an great condition. Is it really 50 years old? Unbelievable!
+Murrat Osmani You're welcome, Murrat. I'm glad you liked the video, and the 55-year-old "patient" that was operated on. Thanks for your kind words :)
great video. thanks. looks like Rusty's found happiness in life..and Jack was almost a victim of an in house fly by..cool amp btw too.
+R HEIDEMAN Thanks, RH. Since we're both getting a wee bit old, Rusty and I now see eye-to-eye on what really matters in life. Jack is generally more aggressive toward the little drone, but, as usual, once the camera is on, the drama suddenly ends.
Lol. Thanks UD
Uncle Doug, once again you have concisely yet thoroughly explained a difficult subject. (It is not surprising to discover you were an algebra teacher; much respect sir!)
Here's a question about resistor wattage in the context of longevity: do higher wattage resistors tend to drift less over time, and does it depend on the material? For example: an amplifier from 1971 has a 15k 1/4 watt resistor in the tone stack, 100k 1 watt plate resistor, (both carbon based,) and 1k 5 watt ceramic resistor in the power supply. If one were to test the values of all three, assuming they were within 5 - 10% tolerance when the amp was built, which, if any, would remain closest to its original value 45 years later? (Assuming, of course, that the amplifier was all original and in good condition.)
Thank you once again for sharing your knowledge!
You're welcome, Michael, and thanks for your nice comments. It's hard to predict exactly how resistors will hold up over time. A lot depends on the current they face, which varies widely throughout the circuit. I would guess that the old fashioned carbon comp resistors would be the worst, and modern metal film resistors would be the best. In between are the carbon film resistors that many of us use. I would think that higher wattage resistors would be more stable than low-wattage (especially puny 1/4W....which I never use) simply due to the larger mass for heat dissipation.
I stay every day looking if you put something new video in your channel. That's like a food for my brain and my soul. "I'm addicted on Uncle Doug Channel"
Master, do you have some other site to view these schematics beyond the "Old Frets"?
Thank for share a piece of your life and time with us!
+Humberto Martins Ferreira Junior Thanks so much, Humberto. In some cases, like the Supro Tremo-Verb, I post the schematics on my own site and provide links in the video. I guess I could start doing this more often. Thanks for watching and for the suggestion.
+Uncle Doug It's a biiiiiiig pleasure to me to watch your channel ^_^
Maybe we could make some logo "Uncle Doug Channel" and print it on a t-shirt :D
I have been thinking about that, Humberto, and may get some Uncle Doug T-shirts printed up. Glad you are enjoying the videos :)
Excellent vid, Uncle Doug, as usual...
+chokkan7 Thanks :)
why you are so outstanding.... Grace teaching style......
Thanks, B. I focus on communication, rather than trying to sound smarter than the audience.
What a wisdom@@UncleDoug
Thanks :)@@beatleswen
Thanks Uncle Doug. I'm sure that was an elementary question but helped me with my notes trying to learn at my age.
No problem, Tom. We're always glad to answer good questions.
Hi Uncle Doug. After scouring the internet for better understanding of how tube amps work, your videos have really helped me clear the fog. I have a "learning handicap" in the sense that I find it difficult to assume things and move on without actually understanding how things exactly work, the purpose of each component etc. Your videos have been a cut above the rest, in that, you do not assume that the viewer has prior working knowledge or that something is too obvious to explain. You actually explain the function of every component. I really appreciate this. Thanks for your efforts.
In the schematic you show, I have two questions
1. In the first input stage there is no cathode resistor. Can the circuit still work satisfactorily? As I understood from your other videos, the cathode resistor serves to put it at a more positive voltage compared to the grid for biasing purposes. Here both grid and cathode are effectively grounded.
2. What is the purpose of the capacitor on the primary winding of the transformer connected to mains supply. It looks like a filter cap but why would I need to smooth out the input AC voltage?
Thanks again for your time.
1. There's more than 1 way to bias a vacuum tube- "grid bias" works equally well.
2. The capacitor on the AC line is there to filter out noise coming in on the power line.
@@daleburrell6273 Thanks Dale
The Teach is back. thumbs up.
+MrMac5150 Thanks, Mr. M :)
Love this series!
We're glad, Sergio :)
great video Mr Doug
+Ulises Aguilar Thanks, Ulises :)
Hello Doug. Another very well done how to video. So well done I could even understand how to do it. And that's saying a lot ! Very happy to see Rusty and Jack in the video. Jack could be Molly's twin no kidding. Thank you again and much respect Doug.
All my very best. Oh and looking forward to your next video in this series.
Bobby
+Bobby Tectalabyss Thanks, Bobby. I'm glad the video was clear and helpful. Our regards to you and Molly. Thanks for watching :)
Great videos! I like them alot. I had a thought about drawing the B+ from pin 8 of the rectifier. It matters if you ever intend to use a solid-state plug-in rectifier instead of valve rectifiers. I hade my amp wired to take the B+ from pin 2, which was all fine. Then I plugged in an octal socket solid-state rectifier I had bought. The new rectifiers cathodes were only wired to pin 2 causing my amp to draw all the amps current through the 5V filament winding. Which might be bad, I don't know. But drawing B+ from pin 8 seems to be standard in most circuits you see.
Thanks for your nice comments and helpful input, Ske :)
Just totally awsome, thank you so much.
You're welcome, IG :)
6:56 Stock as a what? I haven't heard that expression before. Googled around, but I must admit my ignorance. You've set yourself up for an excellent mini-series here, Uncle Doug. You could highlight just about any aspect of amplifier circuits, layout do's and don'ts, capacitance, inductance, etc. You're booked right up until we put you in a home--or they put ME in one... Another delightful video, suitable for repeated clobberings over my head for retention. My highest compliments again. And that Gretsch is certainly NSFW. Nice.
Ironic, really. I have had nothing but fear and dread toward all Algebra teachers to date.
+JC Haywire Greetings and thanks, JC. "Stock as a stone" is an old saying we used way back (1960's) when drag racing our hot rods on the backstreets of town. It implied that an engine and running gear were completely original, which (unlike my video usage) was almost always a lie.....especially if money was going to be wagered on the outcome. I've been touching lightly on all the topics you mentioned, but now intend to go into a bit more depth, which will require an infusion of math. Hopefully, the approach I take will overcome old fear and loathing.
+Uncle Doug On second listen this afternoon, it was quite clear. Maybe I had ear mites this morning. Tinnitus? Hard to say.
Pardon?
Sorry! That's Brit for 'Say what?'.
using resistors that are twice as large as what they're likely to encounter is a very good idea and i'm doing that in the project i will start soon
It costs a few cents extra, looks neat (kind of old fashioned), and is cheap insurance against failure.
very helpful video doug.. thanks!
Im not sure Jack was impressed by the drone!
+Cawfee Dawg You're welcome, CD. Generally, his fur sticks up all over and he jumps around like a lunatic, challenging the drone, but (naturally) the moment I brought out the camera, he became a passive observer rather than the wild cat we all know and love :)
Really Interesting video! A few questions came to mind as I watched it:
1) Why doesn't the cathode on the first 12ax7 have a resistor?
2) What is the purpose of the .001 coupling capacitor that bypasses the volume pot on the way to the grid of v2? Does this mean that the volume can never by completely shut off since some of the amplified AC signal from v1 always gets to the grid of v2?
3) Why does v2 have a larger resister (270k) on its anode DC power than v1 (100k)?
P.S. Rusty and Jack need a patreon page so folks like us that appreciate their hard work can upgrade their treats and toys!
Thanks for the great instruction.
-Gerald
1.) By reducing (in this case to zero) the cathode bias resistance, plate current and gain are maximized. Circuit designers have all sorts of reasons for selecting component values, and sometimes their choices are hard to explain.
2.) A capacitor that bypasses a volume pot is to allow high frequencies to get past the pot resistance unabated.....i.e. it enhances high frequency.
3.) Both anodes are within V1, Gerald. Plate resistance is used to control the output of an amplification stage. In this circuit, V1a has lower plate resistance (100K) and lower output than V1b (270K). Apparently the circuit designer felt that using lower output from V1a to drive V1b produced better tone.
Rusty and Jack do have a Patreon page, Gerald. If you watch some of our more recent videos, a link is provided. Thanks for watching and commenting.
on 2) Does this mean that you can hear the high frequencies while playing even with the volume turned all the way down? It seems like it would, but I'm kinda surprised an amp designer would do that if so.
on 3) Yeah, I realized that I should have said something like V1a, V1b vs V1, V2
2) No, since the VC resistance is to ground, once the VC is turned to zero, all signal goes to ground. However, once the VC is increased, treble frequencies will be able to avoid the resistance of the VC pot and will be accentuated.
Ah, the current takes the path of least resistance. Totally missed that. Thanks for the explanation!
The first half of the 12AX7 is 'grid leak biased'. The few electrons which hit the grid develop a negative voltage at the grid across the high value 6.8M resistor which is enough to bias the tube.
Thanks for sharing your knowledge!!
Thanks for watching and commenting :)
Power : Defined as when one’s wife threatens to divorce you because your spending too much time working on amplifier circuits. Boy iam going to miss her!!! Hahaha 😂 Glad im not married!!
Thanks Uncle Doug your videos are so intriguing that Iam now fully engrossed in learning all about tube electronics despite having an Associate Degree in Electronics Technology that i earned back in 1995.
We learned so much solid state theory then but sadly, didnt learn repair techniques much then back in the early ninetees. We were more focused on design and the ciriculum was designed to transfer to a 4 year program or gain entry level employment in the field.
.
I distinctly remember that we built a 50 watt push pull transistor amp that was powered by a low powered sony walkman hihi.. and that was the extent of amplifier design projects we were involved in then.
Sometimes we just memorized information and regurgitated it until it became habit and kept on chugging along just to cover all the information in the semester.
Your style and instruction is superb and i understand everything you show us.
Tubes are so much more interesting and rewarding in my opinion to learn and will always retain a niche use in amplifiers and communications applications in the electronics field.
Thanks so much for all of this instruction iam really enjoying this series and learning alot :)
I'm glad to hear that you have come to prefer tube circuitry, Tahoe. To me, SS vs Tube is like a photograph vs a Rembrandt painting. Both serve a similar purpose, but the latter elevates the subject matter to a much higher level. Thanks for joining us.
Well done as always. Rusty's choice went the way I thought, but love seemed to slow him down a bit. :)) Jack looked to be thinking up all the four letter words a cat might know. :)) Andrew
+bullthrush Rusty did seem to give the portrait of his girlfriend a little smooch....before grabbing the cookie and running off to the bowels of the workshop to wolf it down :) Jack is normally more aggressive toward the drone, but in the video he came off as an innocent victim....probably trying to elicit sympathy (and more cat treats) :)
Thankyou for your time and it was not wasted as l am learning a lot thankyou 😀
You're welcome, Robert. That's good to hear.
I love the clarity of your presentations. I notice that you almost never stumble over your words, using um or uh to fill the gaps. I wonder if you read from a script (doesn't sound like it) or if you were a teacher in your career?
Thanks, Curtis. I do many retakes and edit out the wasted words. No script. Yes, I was a math and science teacher for many years.
Another amazing and incredibly informative video! A request: not sure if you've done this in the past catalogued in another video, but could you make a video on your method of properly discharging capacitors when working on an amp? There seem to be many methods out there, but I have a feeling I'd like to follow your way. Many thanks! -Alex
+Alex Perez Thanks so much, Alex. I have demonstrated the method in the How to Bias videos. I use a 100 Ohm 10W resistor. One lead is grounded and the other is touched to each positive filter cap lug for several seconds to ensure full discharge. You can then double check each lug with a DC voltmeter just to be sure. Best of luck :)
Thanks a 6150 eh? That sounds like the Grand dad of the 5150, lol jk. I really enjoy your teaching & thank you for sharing this knowledge. This is like a great way to relax listening to a real american man that is NOT the numb skulls they make men out to be on TV. You are a Gem Uncle Doug. Gods Bless you & yours.
+Watchman4u You're welcome, W4. I appreciate your kind words and wish you the best. Thanks for watching and commenting :)
Something tells me Jack has encountered that aggressive mini-drone before !! ;) ;)
+Donald Filbert Yes, indeed, and he is usually much more aggressive toward it, in a thoroughly comical way. I interrupted his nap to make the video, so he was still a little sleepy and passive.
+Uncle Doug Such feline apathy can only be explained adequately by catnip. You might need to have a quiet word with him about his recreational habits.
Indeed. He is attending a 12-step program, and has cleaned up his act....but not his cat box :)
Uncle Doug, you're videos are the best! Pass some love onto the furry ones too, plz. At 20:37 you show the circuit requiring .564W to pass thru that resistor (dam)... And you then say double it for safety. Did you not say earlier in this series how that would be like throwing a hotdog down a hallway? How the high wattage resistor would have little affect on the lower flow through the "dam"? I've learned so much from these videos, so thank you so much. But I'm baffled on this one, perhaps you could clarify in the future? 🙏☯️
I don't recall the hot dog analogy, but whenever you calculate the wattage requirement for a resistor it is standard practice to at least double the wattage for safety purposes.
very interesting uncle doug thank you
You're welcome, James.
Like the way you explain all this doug, your videos have been an invaluable resource for understanding these concepts in an easier way. Question? : How is it that you are showing on the schematic that the power going into the tube is coming from the (Cathode pin 8) ground leg? I guess you are just measuring the voltage across the 1 watt (330?) resistor ? Please clarify, Im not seeing this right. Thanks --
Thanks, Vin. The electrons which form the plate current all come from the grounded centertap of the high voltage winding of the power transformer, through the chassis to the cathode of the tube, then flow from the cathode past the grid to the plate. There are various ways to measure the plate current. Please see my videos that explain them.
My Hewlett Packard HP48 will let me plug in numbers and it has Ohms Law & Power built into an equation library. It has the RC RL RCL circuits and phase angle changes in voltage and current, reactance, reluctance, impedance, resonant frequency, inductance, etc. etc.
That sounds like quite a versatile instrument, Seth.
Your pets have made two interesting observations - perceived female fickleness (poodle) and applied aerodynamics (quad 'copter). Great lesson Doug. You mentioned 'Ballast Resistor' at the beginning but not as an application - later perhaps ?
Thanks, Dave. I'm not sure about your ballast resistor question. I use the term to refer to high wattage resistors that are used to reduce voltage by converting it to heat.
I've come across them in automotive ignition (mainly capacitance discharge ) systems - often wondered what their purpose was there...
I have no idea, Dave. Perhaps there are Internet sites that discuss the design of these ignitions.
haha! I have to get a new kitten and a new tiny drone now!
They're lots of fun, Malcolm :)
Great stuff, Rusty (and Uncle Doug). Good content, and excellent presentation. You'd think you taught for a living or something... :-)
+Joe Vannucci Thanks, Joe. It used to be a "living".....now it's a (very rewarding) hobby.
AWESOME as always! Have you been bitten hard by the drone bug? The Nano QX is a gateway quad and I can only imagine what you might be flying nowadays.
Both our video production and drone flying have taken a back seat lately to hot rod building, Q. Hopefully, we will get back into both previous hobbies before long.
VERY GOOD...THANKS!
+ranuts2 You're welcome. Glad you liked it :)
Gorgeous Amp.
Thanks :)
Greetings Doug & Rosty!!!!
+Victor Martínez Armijo Hi, Victor :)
Super Nice applications for Amp Analysis.....using the lesson. Works better in my head. ps: the Director, Actor, LIghting, Writing guys that work for your Videos are really good.....(they may want to know about paypal's tip jar)----they are that good! KaChing!
+Brian Hensley Thanks so much, Brian. We appreciate your kind assessment of our efforts, and are glad it was helpful.
Uncle Doug! Did you take a bite out of the doggy biscuit bofore giving it to rusty?
Food for thaught.
I think your vids
Are very informative
Educational and done with excellence
Thanks.
You're welcome, Dwight. Yes, I did, and they all tasted the same to me ;)
Hi Uncle Doug, another great video, thanks. I have a question related to resistors, I am planning to scratch build a Fender AB764 amp from parts found at garage sales but am a little confused regarding potentiometer selection. The schematic I have only specifies values needed but not type (A or B). Does it matter or is it important to use the right type for volume, tone etc. Any guidance would be very much appreciated.
+Tony H If you're wondering about Audio (Log) Taper vs Linear Taper, I suggest using Audio for tone purposes.....volume, treble, midrange, bass,etc. and Linear for purely electrical purposes, i.e. variable bias control, etc.
Thank you Doug.In this video you use the term "voltage drop".
Is this always the voltage measured across a resistor and that term is "voltage drop"?
So the voltage drop is the number you use in the many calculations where "V" is a factor?
The term "voltage drop" is not to be confused with any other voltages like the 6.3 filament or 5vac.These are set voltages.
I think I get it now.
Thank you
+Tom Ward I understand your initial confusion, Tom. The term "voltage" can be a static (or "set") term, i.e. to describe the output of a battery or power transformer winding, i.e. a 6V battery.....or it can be a dynamic term, as in "voltage drop" which reflects the amount of current flowing through a resistor, and the different voltages available on either side of the resistor. Voltage drop only exists when current is flowing through the circuit, and it is the value to use in any formula that includes "I" or current (i.e. Ohm's Law).
Volts are used as the units of measure of two different but related quantities. Potential, a.k.a. 'voltage' is the amount of 'electromotive force' (e.m.f.) available to force a current (electrons) to pass through a resistance. Potential difference (p.d.) a.k.a. 'voltage drop' is the difference in potential (voltage) between any two points in a circuit, e.g. the two ends of a resistor. If we have a 6V battery, we can decide that the negative terminal is at 0V, which means that there will be a voltage (e.m.f.) of +6V at the positive terminal. If we connect a resistor between the terminals, one end of the resistor is at a voltage of +6V and at the other end is at a voltage of 0V so there is a voltage drop (p.d.) of 6 - 0 = 6V across the resistor. If we replace the single resistor with two equal value resistors in series, the voltage (e.m.f.) at their junction is +3V, so there is a voltage drop of 6 - 3 = 3V across one resistor and a voltage drop of 3 - 0 = 3V across the other.
Another brilliant video, thanks. Do you have one that works backwards - how to calculate expected voltages and currents/power in a valve circuit without having the actual circuit built i.e. I want to build an amp but do not know voltages apart from the HT or wattages for each resistor???
Ohm's Law works both ways, Dave, but to calculate a value for either Voltage, Current, Resistance, or Power......you need to know two of the values in order to calculate the third. So to determine the Current, you would have to know the Voltage and Resistance, and so forth.
@@UncleDoug Ah ok, thats where it gets tricky - I guess on an amp i would start at the pre-amp end and use the published tube current and voltage plus the series of dropper/filter resistors to gusstimate resistor wattage etc?? I'll have to play with some diagrams I think
Very good demonstration Uncle Doug. I found it interesting on the Resister wattage. Now I have some 2 watt 270k & 470k ohm resisters I have been using in filter Cap usage. All seems to be ok so far. Now this is over kill I'm sure but could it lead to an issue? In my schematic some of the 270k ohm resisters have 10% wrote by the resistance value.
Thanks, Kevin. There is no problem using resistors of a higher wattage than necessary.
@@UncleDoug Thanks Uncle Doug for clearing my mind on this. Appreciate it.
wait? jack is controlling the drone with his mind?!?!
You should make a Best of Rusty video.
+Douglas Gilliland That's a great idea, Doug. Sometimes I go back to old videos and have to chuckle over his antics. Maybe a "Best of" anthology would be a hit.
Hello uncle Doug. I am new to ohms law and finding it facanating.
Q. in the cathode bias resistor,356 ohms. why would you ground/earth it as shown in the
schematic?
I conceed that I have missed some thing fundamental here. Great video.
+neddypong Greetings and thanks, NP. Cathode bias resistors always have one end connected to ground. Ground is the source of electrons for the cathode and the voltage drop that provides the net negative grid bias.
Uncle Doug, amazing video as always! :)
When you're measuring the resistance in-circuit, aren't you actually measuring the resistance in parallel with the whole circuit?
+Olivil Thanks so much, Olivil. In the case of the measurements I took, I don't believe this is the case. Looking at the schematic, the cathode bias resistor and OPT primary are isolated from the circuit and thus not in parallel with any other resistance.
Hey Doug. I noticed on this example you measure plate voltage from plate pin 3 to pin 8 cathode instead of from plate to ground when using the cathode resistor method.. They are the same i guess. If there is a difference please let me know and if it does not matter I'll just use either way. Thanks
In grid-biased circuits, PV is measured from plate to ground. In cathode-biased circuits, PV is measured from plate to cathode (which has a higher charge than ground).
Thank you sir
In my school (portugal) they taught volts as U instead of E (E is for energy in joule, J), so it took me a little while to understand some equations. Is it one of those US and EU preferences/disagreements in notation? Also, when you taught/teach physics how do you teach your students the notation? Thanks for the videos!
As I recall, P = Power in Watts, V = Volts, and I = Current in Amps, Henrique.
1:52..."E" for "Electromotive force" and "I" for "Intensity".
That answers my question...
Thanks UD.....Carl
+skycarl You're welcome, Carl :)
Digging your videos Uncle Doug!
Any recommended websites to order variety packs of resistors and capacitors?
Thanks, GS. I get all my components from Antique Electronic Supply.
@@UncleDoug Thank you!
Very good Doug! Theoretically wasn't Rusty's "first contact" with the photo of his lady-friend? ;) So how does an Algebra Instructor become so versed in electronics?
+Tony Manns You're right, Tony. Maybe I misinterpreted his reaction, and love did win out after all :) My hobby (and eventual business) of restoring vintage jukeboxes in the 1980's required the ability to repair their amplifiers, speakers, mechanisms, wiring, and complex electronic components. Through experience and independent study, I developed the necessary skills to perform all aspects (other than chrome or nickle plating) of a full restoration myself. This same knowledge and skill, combined with additional experience and extensive independent study, allows me to do the same with guitar amplifiers.
Hi Doug :) Thank you for this Video and all the other informative and well done work...Have to say.. Anode Current and Cathode Current Minus Screen Current, Very interesting and begs the question....with regard to Tube Matching....Would it be possible to Build a Tube matching device other that a tube tester for matching output tubes..?
Also,,Can you do a Video on Tube testing...Triodes preamp tubes and power tubes..Thanks Doug.. Terence.
+Terence Kaye You're welcome, Terence. The primary source of variance between output tubes is the amount of current they conduct, which is largely based on the age and condition of the cathode. As tubes age, their current capabilities diminish, their bias gets "cooler", and they begin to sound rather "dead". Tube matching, in my experience, is simply grouping tubes with similar current conduction. Any device that could power up the tubes (heaters, screen, and high voltage) and measure current conduction would work. I simply use the amplifier itself.....insert different output tubes, and measure the plate current of each, selecting two that are quite close in value.
Tube testing would not be a particularly riveting video topic. You plug in a tube, set the dials, push a button, and get an emission reading......and the specifics of the process differ greatly from tube tester to tube tester (so the video would only relate to the tester used) ......but this is not how tubes are matched. Tubes with similar emission values may have very different plate current readings.
+Uncle Doug Hi Doug.. Thank you...It's amazing just how complicated Tube matching can sound given the many different angles....Thank you once again Doug,,,,you truly are a wonderful source of inspiration...Will have to show you the Guitar amplifier I've just completed.....And I have an Idea for a Tube matching set up as well....This could get interesting.. LOL....
You're welcome, Terence. You can post photos of your amp on my Facebook page: Uncle Doug's Vintage Amps. Before you start designing all sorts of tube matching devices, recall that any amp can be used for this purpose, simply by inserting tubes and measuring their plate current.
Hi, Uncle Doug!
I’m from Brazil and I want to design my own guitar amps. I have some questions:
When one could say that a circuit is an original design? This Gretsch 6150 has a very similar circuit to the 5F1 Fender Champ. It is a clone or an original design?
Your channel is a gold mine! Thanks for everything!
Greetings, Rodrigo. In my opinion, there are no "original" tube circuit designs. Way back in the 30's and 40's, RCA engineers designed virtually all the tube circuits imaginable, and every amp since then has used most, if not all, of the circuitry they designed.....so both the 6150 and the Champ are actually derived from their earlier work
@@UncleDoug Thank you!
My freshman electricity 101 class was taught by Sister Thomas Moore, we called her "Sister Resistor"...
Did you greet her each day by asking, "Watts up?" :)
Hello Doug, in a double ended PP EL84 Class AB amp with a 300V B+ into pin 9, 295V out of the plates@ pin 7 and bias resistor of 130 Ohm from pin 3 (which also includes a 25 uF cap), the power rating of the resistor I have seen is 10W. This seems high. Is there a reason for this. Perhaps because there are two power tubes?
+allanpennington If the tubes share the bias resistor, then the wattage would be doubled, and (like horsepower and money), bigger (wattage) is way better than not enough. It would be helpful to know the voltage drop across the cathode bias resistor. The bypass cap would have virtually no effect on the plate current.
Another newbie question for you Doug. At 8:43, is it possible to determine plate current just from looking at the schematic? I am looking at a schematic and I have the plate and cathode resistor values and the B+ voltage at the transformer, but not the voltage drop across the plate resistor. It's a 12AU7 tube. Any tip on how to figure that out?
Not that I'm aware of, Joel. There is really no accurate way to predict the plate current without taking measurements during normal operating conditions. One main variable is the tube itself.......they all tend to vary in PC levels.
I wish i didn't have to ask questions Doug but i'm not the sharpest knife in the drawer. I guess if its grid bias you can't use the cathode resistor method since the cathode is grounded and you could go from pin 3 to pin 8 of the 6V6 or you have to use the OT measurements to determine voltage and bias with a fixed bias amp. I was just curious about cathode bias and getting plate voltage from pin 3 to pin 8 and if pin 8 and ground were at both the same potential in a cathode bias amp If you think my questions are silly or tedious i'll get the hint if you just don't want to respond. I was good with measuring voltage at the plate by measuring pin 3 to ground and then i saw you use pin 8 instead of ground and was wondering if that was just for fixed bias or cathode bias as well? I keep watching your videos since they are fantastic and it troubles me i can't figure it out without having to worry you about it since you probably already gave the answer. Thanks
In cathode bias, you can measure the voltage drop across the cathode bias resistor to determine gross PC. PV is measured from plate to cathode. In grid bias, you measure the voltage drop across the OPT winding(s) to find PC. PV is measured from plate to ground.
May I asked a Question? I have a 50 watt 6v6 powered amp. it's push pull, I've removed the two outter tubes , one died on me. So I though it would be nice to cut down the power on this one is that Dangerous? In my understanding it is not. Also what other power tube could be exchanged for the 6v6's? Thanks
+Watchman4u I am guessing that the amp had four 6V6 output tubes and you removed two of them. You have to be careful which two you pull. If the amp still works and sounds OK, then I guess you were lucky. There are Internet sites that discuss this issue. You might want to do a Google search and read up on it. Since you have pulled two 6V6's, your power transformer could probably handle a pair of 6L6GB's or 5881's without going up in smoke. You should check the tube bias.....they will probably be rather "cold" otherwise.
Uncle Doug Yes 4 Power Tubes I pulled the outer ones. Yikes I thought it could be either or two inside or the two out side. Thx I didn't know that I've read about people using 6L6's in just Two sockets of four of 6v6 amp, to compensate for the power difference, I'd like to get a EL34 sound . I never own one the 6L6 Fender Twin is what I used for years w/a ss amp in stereo live. Then I got the 5150 w/2 4x12's wow Loud never had it past 4 1/2 ever on stage I played @ 3 with the soundmen going nutz screaming please turn down. Thats a Monster Amp & 16 ohm speakers 100Watt they don't break up easy a Clean amp sound Good thru them 5150 Cabs Sheffield speakers. I wish I could mod the thing to get a cleaner clean oh & Tank w/springs.lol Maybe they left that off because the amp moves you the Ev's coming outta the speakers would blow my pants leg. Sound pressure I see guys Crank them things w/Distortion in front of it. Insane. Too much. I did some good blues recording SRV Clapton Jimi sound w/Almond Bro's in there a guys amp blowed up during tracking in my studio so we used the 5150 till we could over dub with his amp when he got it fixed it sounded so good like an Hot rodded Fender Twin I need to get those tracks & share em. Thats a great player in Athens Ga. Gifted young man. Thanks for the advice never mind the rambling I love this stuff I don't like Hi Tech.lol
+Watchman4u I believe you did the right thing, although a schematic would be necessary to be sure.....the two outer or the two inner are usually the ones to pull. Since the pairs are wired in parallel, you only want to pull one from each pair so you still have push-pull alternation. Pulling both tubes from one parallel pair would not be good. As I said, I believe you could get away with two 6L6's as long as they are the only output tubes in place.
I was flying the drone in the house, my dog brings me a feather.
Sounds familiar, Walter.
How practical is it to rewire a dual 6973 output over to EL84 ? I'll wait on your very very professional answer with baited breath. Thank you very much. Love your videos. Say hi to the crew for me thanks.
To me, it makes good sense. You'll have to rewire the socket, naturally, and you may have to reduce the plate voltage for the EL84's.
@@UncleDoug Yes ,thank you . 6973' s are hard to find. Great stuff 👏