I am a physician with absolutely no musical talent, but an endless thirst for knowledge on all fronts, including circuit design. I ended up here after searching for videos on how tube amps work. I've been up for hours watching your videos. Your patient and thorough explanations are incredible. Thank you for your time and effort in contributing these videos to the collective knowledge base that is the internet. The world is a better place because of them!
Oh absolutely! If you’re into vintage amplifiers this is like a technical education. So valuable. I know a younger fella here in New York that owns his own shop repairing and restoring these beautiful creations and cites Uncle Doug as his influence and inspiration. That’s how far this amazing work reaches!
Thank you very much. I've tried so hard other the years to understand amplifiers and nothing stuck in my head. Your explanations just made it click for me somehow, very clear and concise. I feel like a complex subject finally fits inside my small brain 😁 I very much appreciate these videos. Subscribed. 👍
The absolutely best presentation I have found! The best parts are the LARGE simple drawings and the physical tubes and electronic components that mirrors, emphasis and tie everything together! Great work! Will continue to watch more of your series!!!
I’ve been binge watching your videos. You use great analogies to explain the concepts, yet keep enough of technical aspects to have plenty of aha moments. Keep up the great work!
Agreed. I built a few amps in the early 2000s and due to life interference dropped it a few years later. There were forums to learn from, and I learned a lot back then, but having the visuals makes the learning process so much easier to comprehend. It is inspiring me to pick up some of my old unfinished projects.
High quality teaching Doug. Simple, well thought out lessons. Camera play and editing are straight. I dropped out 30 years ago because I could not visualize what circuits do. This is so plain to me now, thanks Doug for taking the time and effort. Time for me to build an amplifier...
Actually, I have an odd question. I have a reason why for this train of thought other than purely electronic, so bear with me sir. I want an AC power supply at 108V @ 54Hz. Could I achieve that with an AC to AC transformer and/or some sort of oscillator? I have no idea except a circuit I presume changes 110V@60Hz to 230V@50Hz?, or is that a simple switch? Is this even do-able? Thanks for any input.
You don't mention the current capacity of his power supply, CN, but it's an important factor. As far as the 108VAC, this would be easily achieved with good accuracy using a Variac. You can also use an inverter to convert DC into AC of varying frequency by altering the frequency of the oscillator withing the inverter. Here is an excellent source of info: electronics.stackexchange.com/questions/148023/how-to-change-the-frequency-of-ac-supply
I know I'm popping all over your videos like the popcorn electrons on a cathode, but I was in a complete fog about rectification tubes etc. and their use of and filtering..! I spent the last 13 or so minutes with your video and the 'Fog' has cleared Doug. Fab explanation. Thanks..Ed U.K.
I love your handwritten and hand sketched tutorials. Your drawings are very clean and to the purpose. I would only like to express that if you are using two-diode setup, your transformer will have 2×V output, whereas bridge rectification requires only V output from the transformer, V being the desired output voltage. Since 2×V capacity transformer will have double the secondary windings of a V capacity transformer, it contains more copper and therefore it tends to be more expensive than the latter. Very informative video as always and thank you very much for it.
I'm blown away by the wealth of information you provide on your channel. I'm just getting started learning about tube amplifiers and am very excited to start digging in here. Thank you SO MUCH for sharing, sir.
Wow, I have watched a few of your videos in this series. You have totally demystified many of the questions I didn't even know how to formulate to ask. You have a teaching gift, Sir!
I know this is an old video but....AWESOME video! MORE! MORE! I learned a ton so quickly....I am 56 years old, with 9 vintage tube amps, and have been wanting to apprentice at a repair shop for years to try to learn more about circuit analysis on tube amps. There just arent any shops within a few hundred miles of me, so I try to pick up what I can on here. Great explanation! Cant thank you enough and really want more. ALL my amps need attention, but shipping a 65 lb tube amp costs a small fortune. So I'm trying to learn more myself.
Thanks for your very nice comments, B. You have the right attitude.....It's always better to pursue independent ability than it is to rely on others. Best of luck with your self-education.
Thank You, Uncle Doug and Rusty. I was thinking I needed to go through all your videos, several times, to "wrap my head around" "IT". I am finding once or twice is clearing up so much that I didn't exactly understand. You (and Rusty) are excellent teachers. I Thank You again, dear Sir.
You are quite welcome, JL. We're glad to hear that the videos are helpful and easy to digest (Rusty's favorite word). Speaking of whom, Rusty is actually the "brains" of the operation, I am simply his servant and provider of ear scratching.....in fact, that's my official title in our partnership agreement :)
Thank you, DN. Over the years, I've found most explanations of electronic theory to be utterly confusing and overly complex.....even though the principles themselves are actually rather simple. After struggling to learn about these topics, I am now trying to "translate" them into basic language and make them more accessible.
I find this gentleman an excellent teacher, I have learnt more watching these videos than any book that I have read. I would like to see how to use an oscilloscope and what voltage you can put into the oscilloscope with out damaging the scope or my self. Please keep these splendid lectures up and thank you. Lionel (uk)
You're quite welcome, Lionel. I appreciate your kind appraisal. I haven't made a video featuring the oscilloscope, mainly because I'm not sure how many viewers own one, but I will definitely consider your suggestion. Thanks for watching and commenting.
Hey, No charge, I should be paying you and the Carlson lab guy, words are nice ,but sharing the knowledge base that has taken you years to develope, and to point blank share it depicts great character, You are a valuable tech. and part of what makes America great, down the road I may ask you on certain test gear, I have more than whats needed for my analog world , and a newbie i Iz. many Thanks Uncle Doug!!! P.S. gotta brag on my latest find, Stopped in at a garage sale cuz traffic was at a stand still and noticed a very familiar looking brief case. a barley used Sencore MU-150 with all the original tags, power cord still factory wrapped. they wanted it gone, and $5 made it land on my bench. replacing all the electrolytics (ESR thru the roof), as I write this. be well.....
You are doing the world a diservice if you are not teaching electronics / electrical engineering at the college level. I've take course work that I didn't understand until finding your channel. Just becuase you can pass tests doesn't mean that you "get it". NOW, I get it... ; )
in another video you mention the 12ax7 tube being two tubes in one. is this why the 12ax7 is more gainy than others further down the list such as 12at, 12ay etc? and also the reason why it uses less current?
Wow, what a good teacher you are! I understood and you made it seem simple and easy as well as provide practical advice. Now when I see a board, I know what the parts do! Thanks!
Thank you, Uncle Doug. Just...thank you. This stuff is the bomb. I'm learning a great deal because you're a great teacher - clear and direct. Lovin' it! Thanks to Rusty, too.
Thanks Doug - useful insight here - never thought about how an indirect cathode on a rectifier gives a more gentle HT switch on to the rest of the valves (tubes!) in the circuit eg allows the heaters to get working first...clearly a better option than a direct one!
You're welcome, David. The difference is quite evident when using an indirectly-heated rectifier vs a directly-heated one. The first time I used a GZ34, it took so long to come on that I initially thought that the amp circuit was faulty :)
I just wanted to let you know that you answered all my questions about the inner workings of an amplifier - this is true after I read the "Inside Tube Amps" by Dan Torres. Thank you so much! I'm ready to put my amp together now (I've had the parts for about three years, but I hate to attempt things I don't fully understand.) PS: Don't worry, I've built PSUs before and know about safety measures for high voltage high current, and cap discharge etc. Thanks again, excellent videos in layman terminology.
Thanks for posting this. I've always enjoyed the sound of tube amps, and tinkering with electronics. Recently, I've been itching to building my own tube amp (but I don't play guitar ... weird, I know). Before I pull out the soldering iron, I want to understand more about what is actually happening inside the amp. It looks like I'll be spending a bit of time on your channel in the coming days.
You're welcome, Jon. Hopefully the videos I have posted will give you a basic understanding of amplifier circuitry. Best of luck with your pursuit of knowledge.....and your project.
Dirty uncle Doug! Thanks for the video. MY kx15 crate amp was buzzing really loud, and there was something loose inside.I resodered the loose part, but I forgot which wires went where... now trying to learn a lot.thanks again, peace
+alex thefakest You're welcome, Alex. It's good that you are trying to learn as much as possible to enable the repair of your own amps. That's always the best place to start. Best of luck with your project :)
Hi, Unclr Doug, here's a good one. I'm rebuilding a Newcomb AV-7 phonograph with a Widow Maker circuit. It has a a 12av6, with dual diode and a triode in the same glass envelope. The diodes are connected in a half-wave configuration, and a solid state diode is connected in the heater section. I've seen a similar circuit using a single diode tube, and a SS diode in the heater section.
@@UncleDoug Thanks for all of the Videos, and for your reply. After weeks of study, and searching for an isolation transformer that never existed, I tend to concur. Current draw on a 'Widow Maker' is enormous. But it was a great case study in archaic engineering (and finding obsolete parts), and I did find an excellent source for schematics: ''Practical Amplifier Diagrams'' (Robin & Lippman, 1947). You, and your fan base, can download a PDF copy for free.
A very thorough explanation, thank you. After running some simulations in LTSpice, I completely understand your preference for the soft start of the GZ34.
Doug, this is a great explanation, best I've seen yet. If you get a chance to make another video, could you please go further into depth on tube rectifiers and how is it that we get the B+ off of the cathode. Also, how does the current flow through the anodes since it appears to be a seemingly open circuit. I'm assuming the anodes don't touch.
there are many great videos here that help tremendously. But what about repairs and identifying distortion and other enomolies in existing new and vintage amps?
I'm working my way through all your videos UD&R. You are hitting on all the topics I have questions about. It's like you're reading my mind. I understand the electronics from a numbers side, but never understood why "filter caps" were in audio circuits. This video filled in some big gaps for me. THANKS!
You're welcome, Greg. I try to cover all the topics that puzzled me when I started out with tube amps.....and, apparently these topics coincide with other people's areas of uncertainty. Rusty and I are glad the videos are helpful :)
Uncle Doug, I have a few questions for you and please explain them : 1. What is 169VDC RMS !!!!? 2. What is pulsating D.C.? 3. If I need +270VDC, using a two-diode full-wave rectifier, how many volts should the transformer secondary be? 4. What is the P.I.V. of a diode? 5. What is 120Hz hum!!!!? 6. Why is a computer power supply so special that deserves a mention? Looking forward to hearing from you, Uncle Doug. Paul Cheung
Thanks, Christoph.....I really appreciate your kind assessment. I have several other technical videos that may be of interest. Please check my most recent posting on Output Tube Biasing.
Great info, thank you. I am trying to fix a home audio amplifier and was hoping you could help me troubleshoot it. The bridge rectifier on the power supply board emits a large spark when I power it up though it continues to work. I replaced the bridge rectifier and 2 small caps next to it and the problem remains!
Since bridge rectifiers are generally sealed blocks, I'm not sure where the sparks could be coming from, MT, but it sounds like the start-up voltage spike exceeds the rating of the BR. If the BR worked fine for a long time and suddenly began to act up, perhaps your filter capacitors are drawing more current than they should. You need to evaluate this before sacrificing another BR. It may be time to change the filter caps.
Are the filter caps the large ones (6800uF 80WV)? The spark seems to originate at the + lead of the bridge. You can see photos and video at this forum post: forum.allaboutcircuits.com/threads/home-audio-amplifier-repair.128825/
Hi Uncle Doug, thanks for your comments recently on the output transformer video, where I was asking about an old amp I am fixing up. I have a speaker I am going to get out of storage to test it with. In the meantime I have taken the back off and started to map out the circuit and compare it to the champ / vibro-champ schematics. There is something strange about the filter caps - or maybe I should say lack of filter caps. There are two cans on top of the chassis, one marked 8 + 8 uf and one 20 uf, but having looked inside there is effectively a jumper across the first, and the second is not across the rectifier output but along the + rail, with a 400 ohm resistor across the terminals. Will it still function as a filter cap connected like that? I suppose the other cap might have failed and someone might have thought it wasn't worth the cost of replacing it, but I didn't think they were that expensive - would there have been any other reason to take it out of the circuit? As I say I haven't put it through a speaker yet but I am guessing there will be a good dose of hum when I do.
You're welcome, WS. Without seeing the components in person and having a schematic, it's just about impossible to make educated guesses. I think you need to map out the entire schematic, as you mentioned, and then see for yourself if vital components are missing, bypassed, or inoperable. It sounds like there are some problems with the filter caps, and you would probably be better off simply replacing them with new ones (they aren't particularly expensive). This is a dangerous part of the circuit, so be very careful. Do not plug it in or test it without running it through a current limiter (see my video). It will greatly reduce the chances of damage. Good luck.
+jeff b The two tubes are quite similar in design, but have different numbers of pins and different pin-to-component internal connections, Jeff. The 5Z3 was a popular rectifier with early jukebox amplifiers.
cool, did not know that, using the 5z3p in the Hifi with 2- 6N9P'S and 2-EL34-B'S, going to correct all my mistakes after watching some more of your videos 2 or 3 more times as to absorb all the info, happy holidays to you and rusty- sorry forgot your cat's name him too, take care
Uncle Doug - I watched a video where the guy describes the filter caps on the 5F1 as being “underrated for the circuit.” He mentioned that his preference for the filter caps is: 33, 22 and 10 respectively, all rated at 450v- to eliminate hum. But my mind always says there will be some type of trade-off when deviating from the schematic - some good, some bad, and within those values there are all kinds of electrolytic caps, size, tolerances, etc. It’s a jungle out there. In the old 5F1 circuit, and taking into consideration modern voltage at the wall, is it preferable to increase the values of the filter caps, and if so, what’s the trade off’s of doing so? Thanks!
First off, there is no need to increase the values, Chad. A properly built 5F1 will have no hum issues with the original cap values. The downside to wholesale cap enlargement is that the capacitors represent a virtual dead short to the circuit when it is first turned on (to charge the filter caps). When you grossly exceed the design parameters of the circuit, damage can occur to the rectifier tube and possibly the high voltage winding of the PT.
Two years ago, I shopped for a Supro amp. I listened to the Thunderbolt MKII and Thunderbolt+ and found a tremendous difference in their sound, the plus model sounding much better to my ears. Supro support explained that the only difference between the two circuits is that the plus uses a tube rectifier, whereas the MKII uses a solid state rectifier. Does the type of rectifier that's employed generally contribute significantly to an amp's tone? If so, why?
Tube rectification is usually limited to sub-50W amps, Dave. To get 100W usually requires two rectifier tubes, as in some Mesa amps and an unusual model of the Fender Bassman 100.....while diode rectification can easily exceed 100W. Thus, it's apparent that current flow is limited with tube rectification. While this sounds like a detriment, many people, including yourself apparently, prefer the tone created by the "sag" or delay in current flow within the output tubes found with tube rectification.
@@UncleDougthanks for that additional information. As others have said many times, you are a uniquely talented teacher. The difference in sound between the two amps I mentioned was remarkable. The plus amp brought my Telecaster to life. The MKII sounded similar to the Thunderbolt+ through a Koch Dummybox--dull and lifeless.
Another excellent video but how do you choose the resistance and capacitance of each node in order to get the correct voltages? Also how do you calculate the use of a choke? This is probably the main issue I have design. At the moment I just look at what Fender/Marshall etc have done and copy then tweak their design but it would be nice to be able to calculate the values of the components myself. Thanks. So for example I'm building a stereo amp based on a circuit similar to the 5F1 but using a beefier power supply, a James tone stack and 3 stages plus a GZ34. How do I know the capacitors and resistors for each node? My current plan is the steal the values from the Deluxe or Princeton Reverb!
Using data from existing, successful circuits is a good, easy way to get ballpark values for the components in your circuit. You can then fine tune the values as needed. If you wish to start from scratch, you will have to know the current flow through the power supply rail and then calculate the voltage drops necessary for each amplification stage. The trick is knowing the current flow......which requires some guesswork, and results again in ballpark figures that have to be fine tuned. There are no absolutes, only educated preliminary guesses, and subsequent adjustment to suit the circuit. Good luck.
Hello Doug, I have been studying the Vox AC10 schematic as it is a simple 10W tube amp to learn the basics. I note that the PT puts out 300-0-300 to a 6CA4. The +ve output from this tube is 320V. This is subsequently stepped down through a 5 Henries choke to 305 and 255V for the 12AX7 and two EL34's; plus an EF86 and ECF82 respectively. What I dont quite understand is why the 300V input to the rectifier tube, (6CA4) increases to 320V. This is an increase of 6.667%. How do you account for this increase and is there a way to calculate what it might be for other voltage inputs. Why I ask is that this type of PT 300-0-300, 6.3 120mA are hard to come by. If I used a different PT with say 660V total output could I still achieve the required B+ V of +305 and +255 by using a different choke, or preferably a combination of resistors?
allanpennington Greetings, Allan. This is a complex issue. The problem is that AC is measured in RMS voltage, and DC is not. The 600VAC output from the power transformer secondary is equivalent to 600VAC divided by 1.414 = 424VDC . This number is then reduced during rectification, filtration, and choke coil to the +320VDC you cited. If you used a 660VAC PT, the value would be about +350 to +360VDC. This added to the increased wall voltage we now have (compared to when these amps were built) could yield a rather high plate voltage value for the EL34's, which prefer values closer to +320VDC. You may be able to lower this using resistors (which also reduce the plate current and get hot).....but the best bet is to use a proper PT. See Triode Electronics for good PT's at very reasonable prices. Good luck.
Uncle Doug Thanks Doug for getting back to me. I am in New Zealand so shipping PT from the States is an expensive proposition. There is a UK company who make an exact AC10 PT clone which might be an option. We are also on 240V AC house current here so this adds to the complexity when looking at old circuits although I do have a 240 to 120 step down transformer I got years ago when I purchased the first Apple Mac Plus on the way home through the States from England to NZ. I have never had a tube amp and they are so expensive I thought I would give making one a go and I like the tone of the Vox AC10 SRT which was put out in limited numbers. The SRT had a separate two speaker cab and the head had reverb as well. Maybe something simpler to start might be the best bet. Thanks again. I really enjoy your MOI. Thats Army slang for Method of Instruction.
Great explanation Uncle Doug! Thanks.... And as I like to joke abit, back in the day I had a bad bottle of "Ripple" and the next morning my head had a very large hum!! Ok, ok. I'll stop! Seriously though, Ive learned alot from you and greatly appreciated it!!🎼🎛
Ripple was the nectar of the gods back in the old hippy 60's, Wayne. I downed many a bottle of it while listening to Iron Butterfly and Vanilla Fudge albums ;)
Thinking of trying to scratch-build a 6G6B Bassman, in which there are six diodes in a full wave rectifier. Unfortunately, the schematic doesn't say anything else about them. I've found references to what diodes to use, but I'm wondering now if it would be possible to use a "pre-fab" bridge rectifier, instead, and if so, what I should know about the unit.
Stick with 6 individual diodes just like Leo did. You can order them from Antique Electronic Supply for about $2 (total.....not each). Their part number is P-Q1N5408 1000V 3A rating @ a whopping $.35 each.
In videos I've watched the value of the filter caps is often greater than the original spec. Can I assume the value just needs to be enough to always have enough capacity to fill the ripple? Would substituting, say, 100uf cap instead of a called for 8uf be fine to use aside from being overkill and expensive? Thank you, Uncle Doug!
You need adequate capacitance to fill the ripple, as you said, but going too high will stress the rectifier tube on start-up, since big caps draw a lot of current to initially charge up.
Thanks for the video. I just purchased a Panama Conqueror which is a Champ copy. The rectifier is a 6Z4 Chinese tube. Is there a US version of this? Or, is it easy to replace that tube socket with one of the tubes that you prefer? The Panama uses a 12ax7 and a 6v6GT tube compliment. Or, is the 6z4 good enough to keep and not worry about? Thanks for any advice.
So the 5v ac heater windings also provide the cathode output (B+) and like a small ac signal voltage can co exist with a high dc voltage in the same conductor then this is the same principle. Have I got this correct?
+Barry Davison The final statement is correct.....AC and DC can coexist in the same conductor. The 5VAC heater winding doesn't provide anything but excitation to the cathode, which makes the rectifier work. The DC B+ that is produced by the rectifier simply exits via the 5VAC wire.
Thanks so much for these videos Uncle Doug. I'm hoping to get a better understanding of how to select the capacitance of the Filter caps when using rectifier tubes. Is there any chance you have any videos that talk about that? I've been told that you need to be concerned about the in-rush current because the Rectifier tubes can't handle too high and that's why the capacitance needs to be low. I can't say that I understand why higher capacitance would increase that current (but I am just learning).
When an amp circuit is first energized, the filter caps have to charge up, so for a second or two, they are like a dead short....the higher the capacitance, the longer the short lasts. The maximum value for 1st filter cap is given for each rectifier tube in tube handbook(s).
@@UncleDoug That makes sense. Thank you. I'm reading Megantz's book and he mentions that the final stage of filtering is the preamp section and that is because you want to filter it more. So is there a reason that we usually see all low capacitance caps in a row? Why not just the first cap low and then all the rest higher?
Fender uses six diodes, Dave, three on each wire, so from a practical standpoint, i.e. protection from the failure of one or two diodes, it must make good sense.
Are you saying that we cannot hear or detect the negative side of a 60 Cycle sine wave? I have always thought that the humm coming out of my Vox AMP was the sum of one full wave, above and below the null line.
Since the AC is rectified in an amp circuit so that only the positive wave forms are sent to the amplification circuit, there are no negative wave forms to hear. Look at the ripple in the output from the rectifier (in my diagram). It's a small fraction of the total amplitude of the original AC, but it will still cause the speaker to move in and outward at 120Hz, providing the hum associated with failed/failing filter caps. The caps smooth the ripple, charging the DC up to peak voltage and providing a smooth, silent, unrippled DC power source for the pre-amp tubes.
Extremely Useful information!......Uncle Doug for a 5C3 circuit....5Y3GT...would a 5V4 be better? I realized of the slow warm up but if compatible...will it change the sound color or attack of the amp sound/tone signature?
atta1798 Greetings and thanks, Atta. Replacement of the 5Y3 with a 5V4 is a favorable exchange and is said to offer a little more headroom, greater volume, tighter bass, and the tube-saving advantage of slow start up.
I have a peavey tnt 160 bass amp with a "120 Hz" hum. if I bang the top of the amp with my fist, the hum almost disappears but can come back over time. I am wondering, does that mean there could be a bad solder joint between the capacitor and the circuit board or is it just an old dried out filter capacitor due to the age of the amp circa 1985. This is a great amp and it would be a very satisfying exercise if I could fix it. I am thinking if I can put the guts on the bench and wiggle the caps, that might give me a clue to whether the connections to the board are sound? Opinions? Thank you, your videos are awesome.
Kevin Courtney Thanks for the kind words, Kevin. The only source I know of for 120Hz hum is faulty electrolytic filter caps. The fact that the hum subsides when you vibrate the amp might indicate a faulty solder joint on one or more of the caps. If you can wiggle the cap and its connections (with a wooden or plastic stick....not a pencil) you might be able to determine which one is at fault. While you're at it, wiggle the tubes, especially the rectifier (if it has a tube rectifier). Whether or not you can find the culprit, it wouldn't hurt to replace the filter caps. Good luck.
Have a question. How to choose a rectifier tube for the scheme? Indirect heating for the slower warm up - done. But all other parameters? Heater current(HC). Peak inverse voltage(PIV). Max rectified current(mRC). Plate current. What they should be? I'm choosing between GZ30 = 2A (HC), 125mA (mRC), 1400V (PIV) and other tube with 3A (HC), 190mA (mRC) and 1700V (PIV). You said you like GZ34 the most. Why? I can see that it can output more current. has less heater current and has average PIV in comparison to the above mentioned. Are these critical parameters? Thank you. Best regards, Yury.
Good question, Yury. I would say that an ideal rectifier should exceed circuit requirements by a "comfortable margin". If total voltage and current requirements (either directly measured or accurately calculated) were 90mA and 350VDC B+, then the GZ30 would be a good choice, and it's lower heater current would be less burden on the PT. If the V & C requirements were 115mA and 475VDC B+, then I would probably go with the 3A tube. I personally have no exact formula, but simply rely on common sense. In most sub-30W amp circuits, the efficiency, slow startup, and low PT demands of the GZ34 make it an obvious choice....at least to me.
I have a question about filter caps in general. Is it possible to hear difference between filtercaps from different brands with the same value? I have a Marshall jmp 50w amp that uses 3 x 50+50 500V caps and they need to be replaced because they sit in there for 35 years.... I see a lots of brands with different prince tags on them so I wondered they smooth out the ripple so there should not habe been any difference?
+Marco Hermans Marco, are you changing the filter capacitors because they are old....or because they are not functioning properly? If they are working well, I would leave the old ones installed. Personally, I don't think there is any difference in tone or function between electrolytics which are expensive and those which are reasonably priced. Sprague is a good brand, and I've had good luck with Nichicon and the black, German caps (name eludes me). Don't get the cheapest or most expensive caps.....go with the ones that are reasonable and somewhere in the middle.
They've bulbs on two of them so replacement is more of a safety issue to me. I hear a sort of 100 Hz noise when I crank the master volume past 5. (We have 220V ,50Hz in Holland) This is the first time that I'm gonna service an amp myself . At technical school we learned a lot about electronics 30 years ago about transistor amps and not about tube amps (High voltage )That's why I watch all of your video's and learn as much as I can before I'll give it a try. I figured out that buying some decent alligator clips is not a waste of money...Safety first...
Safety first indeed, Marco....be sure the clips are well insulated. It does sound like the filter caps are failing. You might want to make a cap-draining probe. I used an old phillips screwdriver, sharpened the tip, and connected one end of a 100 ohm 10W resistor to the metal shaft and the other end to a grounding wire and alligator clip. Connect the clip to ground and touch each + cap lug for a few seconds. Observe cap polarity (almost always neg to ground) and be careful. Best of luck.
Thanks for the tip . The next step is to check the first pre-amp tube (ECC83) because my amp have two inputs, high and low. Each input goes to one site of the ECC83. The low input doesn't function anymore and the high input does function normally. Clean the sockets.When the amp is serviced I'll make a schematic with voltage measurements on crucial points because I can't find one for the JMP 2104 with EL34 power tubes on internet. Because I wanna keep that amp forever I'll put new tolex and grillcloth on it because that's have been worn out. Your video's teach me everything I need. I'll let you know how it works out.
I have a question and sorry if my english is not good. Can you replace the 5Y3 of the Champ Amp by some tube with cathode?, ¿What happens if I connect the cathode of the new tube only to the "+B" of the circuit and the heater only to the yellow wires? Thank you!
Juan, about the only rectifier with a cathode that you could safely substitute for the 5Y3 would be a 5V4. You would not change the socket wiring at all. Your plate voltage may go up a little so you would have to check it. The high voltage goes only to the plates of the rectifier, never the cathode. The rectifier creates the B+ (rectified high voltage). If I were you, I would stick with the 5Y3. It's a great rectifier for the Champ.
strange amp: 3 Power Tubes? ... I'm not sure how to contact you with an only partly related question so am picking this video that seems at least in the 'how to' range of topics. I have a small 1950s/1960s Filmworks projector amp (volume and tone controls, one input-microphone, otherwise the amp would amplify the film audio) I am going to clean this up and use for guitar and I'm confused about the tubes. The larger tubes are a rectifier (5Y3GT), and then there are THREE 6V6s. That doesn't make sense to me to have an odd number greater than one. Could it somehow giving the mic a power section with one tube and the film audio a separate power section of two tubes? That seems unlikely but I can't think of what else it would be. If you can think of anything that might explain this, without thinking about it too hard, I would be interested to know. I haven't opened it up yet, but am interested in your thoughts.
I have never heard of an amp with 3 output tubes, OM. See if you can find a schematic for it and post it on my Facebook page: Uncle Doug's Vintage Amps. Maybe we can figure this out.
I am a physician with absolutely no musical talent, but an endless thirst for knowledge on all fronts, including circuit design. I ended up here after searching for videos on how tube amps work. I've been up for hours watching your videos. Your patient and thorough explanations are incredible. Thank you for your time and effort in contributing these videos to the collective knowledge base that is the internet. The world is a better place because of them!
Wow.....thanks so much for your very kind words, ADW. We sincerely appreciate them, and are glad to hear that the videos are helpful and informative.
Uncle Doug needs his own t.v. show, he is truly one of the best contributors on RUclips. No doubt about that.
Thanks, SS, but only if Rusty can be my Ed McMahon :)
Oh absolutely! If you’re into vintage amplifiers this is like a technical education. So valuable. I know a younger fella here in New York that owns his own shop repairing and restoring these beautiful creations and cites Uncle Doug as his influence and inspiration. That’s how far this amazing work reaches!
the smartest people explain things in the simplest terms - thanks!
Thanks. I hope our explanations are always clear and concise, EA.
Thank you very much. I've tried so hard other the years to understand amplifiers and nothing stuck in my head. Your explanations just made it click for me somehow, very clear and concise. I feel like a complex subject finally fits inside my small brain 😁
I very much appreciate these videos. Subscribed. 👍
Glad to hear it, KW. Thanks for subscribing :)
The absolutely best presentation I have found! The best parts are the LARGE simple drawings and the physical
tubes and electronic components that mirrors, emphasis and tie everything together! Great work! Will continue
to watch more of your series!!!
Thanks so much, Jeff. We're glad to hear that our videos are easy to understand.
I’ve been binge watching your videos. You use great analogies to explain the concepts, yet keep enough of technical aspects to have plenty of aha moments. Keep up the great work!
Thanks, BGR. Glad you enjoy our methods :)
I'm prepping for my General-class ham radio license and finally found someone who can explain this in a way that makes sense. THANK YOU UNCLE DOUG!
You're welcome, Mason. Good luck on your test.
+Uncle Doug, thank you. Best time I've spent on RUclips lately. I learned more about tube amps from you in 2 hours than I did elsewhere in 10 years.
You're welcome, Don. It's great to hear that the videos are an effective learning tool.
Agreed. I built a few amps in the early 2000s and due to life interference dropped it a few years later. There were forums to learn from, and I learned a lot back then, but having the visuals makes the learning process so much easier to comprehend. It is inspiring me to pick up some of my old unfinished projects.
High quality teaching Doug. Simple, well thought out lessons. Camera play and editing are straight. I dropped out 30 years ago because I could not visualize what circuits do. This is so plain to me now, thanks Doug for taking the time and effort. Time for me to build an amplifier...
You're welcome, CN. Thanks for your very nice comments. Best of luck with future projects.
Actually, I have an odd question. I have a reason why for this train of thought other than purely electronic, so bear with me sir. I want an AC power supply at 108V @ 54Hz. Could I achieve that with an AC to AC transformer and/or some sort of oscillator? I have no idea except a circuit I presume changes 110V@60Hz to 230V@50Hz?, or is that a simple switch? Is this even do-able? Thanks for any input.
You don't mention the current capacity of his power supply, CN, but it's an important factor. As far as the 108VAC, this would be easily achieved with good accuracy using a Variac. You can also use an inverter to convert DC into AC of varying frequency by altering the frequency of the oscillator withing the inverter. Here is an excellent source of info: electronics.stackexchange.com/questions/148023/how-to-change-the-frequency-of-ac-supply
I know I'm popping all over your videos like the popcorn electrons on a cathode, but I was in a complete fog about rectification tubes etc. and their use of and filtering..! I spent the last 13 or so minutes with your video and the 'Fog' has cleared Doug. Fab explanation. Thanks..Ed U.K.
That's great news, Ed. Thanks for making our day :)
I love your videos. Simple, to the point, and informative. Perfect for learning new things at home
Thanks so much, 1PM. We're glad you like them :)
I love your handwritten and hand sketched tutorials. Your drawings are very clean and to the purpose. I would only like to express that if you are using two-diode setup, your transformer will have 2×V output, whereas bridge rectification requires only V output from the transformer, V being the desired output voltage. Since 2×V capacity transformer will have double the secondary windings of a V capacity transformer, it contains more copper and therefore it tends to be more expensive than the latter. Very informative video as always and thank you very much for it.
Thanks for the nice comments and info, LS.
@@UncleDoug thank you uncle. One stupid question: do tube rectifiers have voltage drop characteristics like diodes have?
Not stupid at all, LS. Yes, they do.....because rectifier tubes contain two diodes, so all the same rules apply.
I'm blown away by the wealth of information you provide on your channel. I'm just getting started learning about tube amplifiers and am very excited to start digging in here. Thank you SO MUCH for sharing, sir.
microcosm You're quite welcome. Rusty and I are glad you're enjoying our videos and sincerely appreciate your very kind words. Thanks for watching :)
Wow, I have watched a few of your videos in this series. You have totally demystified many of the questions I didn't even know how to formulate to ask. You have a teaching gift, Sir!
Thanks so much, John. Rusty and I really appreciate your kind words.
I know this is an old video but....AWESOME video! MORE! MORE! I learned a ton so quickly....I am 56 years old, with 9 vintage tube amps, and have been wanting to apprentice at a repair shop for years to try to learn more about circuit analysis on tube amps. There just arent any shops within a few hundred miles of me, so I try to pick up what I can on here. Great explanation! Cant thank you enough and really want more. ALL my amps need attention, but shipping a 65 lb tube amp costs a small fortune. So I'm trying to learn more myself.
Thanks for your very nice comments, B. You have the right attitude.....It's always better to pursue independent ability than it is to rely on others. Best of luck with your self-education.
Thank You, Uncle Doug and Rusty. I was thinking I needed to go through all your videos, several times, to "wrap my head around" "IT". I am finding once or twice is clearing up so much that I didn't exactly understand. You (and Rusty) are excellent teachers. I Thank You again, dear Sir.
You are quite welcome, JL. We're glad to hear that the videos are helpful and easy to digest (Rusty's favorite word). Speaking of whom, Rusty is actually the "brains" of the operation, I am simply his servant and provider of ear scratching.....in fact, that's my official title in our partnership agreement :)
This is great. Clear, concise, and very helpful. You obviously have a lot of knowledge about tube amps and it shows in all your videos.
Thank you, DN. Over the years, I've found most explanations of electronic theory to be utterly confusing and overly complex.....even though the principles themselves are actually rather simple. After struggling to learn about these topics, I am now trying to "translate" them into basic language and make them more accessible.
I love to hear uncle Doug explain things even some very basic stuff.
We're glad you do, Moses. Thanks :)
I find this gentleman an excellent teacher, I have learnt more watching these videos than any book that I have read. I would like to see how to use an oscilloscope and what voltage you can put into the oscilloscope with out damaging the scope or my self. Please keep these splendid lectures up and thank you. Lionel (uk)
You're quite welcome, Lionel. I appreciate your kind appraisal. I haven't made a video featuring the oscilloscope, mainly because I'm not sure how many viewers own one, but I will definitely consider your suggestion. Thanks for watching and commenting.
Thanks Uncle Doug. your sharing is a gift, stay with it, Your production is straight forward and professional. many Thanks!
You're welcome, DN, and thanks for your very nice comments :)
Hey, No charge, I should be paying you and the Carlson lab guy, words are nice ,but sharing the knowledge base that has taken you years to develope, and to point blank share it depicts great character, You are a valuable tech. and part of what makes America great, down the road I may ask you on certain test gear, I have more than whats needed for my analog world , and a newbie i Iz. many Thanks Uncle Doug!!! P.S.
gotta brag on my latest find, Stopped in at a garage sale cuz traffic was at a stand still and noticed a very familiar looking brief case.
a barley used Sencore MU-150 with all the original tags, power cord still factory wrapped. they wanted it gone, and $5 made it land on my bench. replacing all the electrolytics (ESR thru the roof), as I write this.
be well.....
Congratulations on a major score, DN. I guess traffic jams are good for something :)
Thank you for the effort . Your videos are very instructive for us who are just learning about the old amplifiers. Greetings from Croatia.
You're welcome, Robert. It's great to hear from our international viewers. Best regards from Texas, USA :)
You are doing the world a diservice if you are not teaching electronics / electrical engineering at the college level. I've take course work that I didn't understand until finding your channel. Just becuase you can pass tests doesn't mean that you "get it". NOW, I get it... ; )
Thanks so much, TJ. That's great news.
I'm a huge fan of this channel. You're like the teacher I never had. Great video!!
Thanks so much, Matt. I sincerely hope my videos are helpful and informative.....thanks for watching!!!
Whenever I learn something new, I realize just how far Id like to go, thanks!
You're welcome, Michael.
and then there's kirchoff's laws and quadratic equation. backin' up, backin' up.
in another video you mention the 12ax7 tube being two tubes in one. is this why the 12ax7 is more gainy than others further down the list such as 12at, 12ay etc? and also the reason why it uses less current?
excellent explanation. especially appreciate your run-down on tube categories and models.
Thanks, Jex.....glad you enjoyed the video.
Uncle Doug, . . . your videos are so educational and clear. Thank you for sharing your knowledge. Great Deal for us All.
Thanks so much, RD :)
You are such a great teacher. I feel smarter after every video 🙏
Thanks, George. That's great to hear.
Wow, what a good teacher you are! I understood and you made it seem simple and easy as well as provide practical advice. Now when I see a board, I know what the parts do! Thanks!
You're welcome, Bruce.
Thank you Professor Doug for this rectifier lesson.
It was a pleasure, John.
Thank you, Uncle Doug. Just...thank you. This stuff is the bomb. I'm learning a great deal because you're a great teacher - clear and direct. Lovin' it! Thanks to Rusty, too.
You're welcome, Shaun....from all of us :)
finally I understand rectification, Uncle Doug your the BOMB!!! give rusty a treat for me!
+jeff b Thanks, Jeff. Rusty and I are glad the videos were informative :)
8:03 - those two really don't look happy... ;)
Great clarification, as always, Doug!
Thank you so much for all your work!
Those cathodes are definitely displeased about something, JT :) You're welcome.
Thanks Doug - useful insight here - never thought about how an indirect cathode on a rectifier gives a more gentle HT switch on to the rest of the valves (tubes!) in the circuit eg allows the heaters to get working first...clearly a better option than a direct one!
You're welcome, David. The difference is quite evident when using an indirectly-heated rectifier vs a directly-heated one. The first time I used a GZ34, it took so long to come on that I initially thought that the amp circuit was faulty :)
Very good explanation of rectification.
Thanks, Mark.
I just wanted to let you know that you answered all my questions about the inner workings of an amplifier - this is true after I read the "Inside Tube Amps" by Dan Torres. Thank you so much! I'm ready to put my amp together now (I've had the parts for about three years, but I hate to attempt things I don't fully understand.) PS: Don't worry, I've built PSUs before and know about safety measures for high voltage high current, and cap discharge etc. Thanks again, excellent videos in layman terminology.
Alexander Brevig You're quite welcome, Alexander. It's great to hear that the videos are helpful. Best of luck with your amp project :)
Hey Doug! Love your vids, I know about these concepts and watching your vids just makes all my doubts go away!
Glad to hear it, Sam. Thanks !!
thanks Doug. your part 1 amp video explains it perfectly . I don't how I missed it!!
+Barry Davison You're welcome, Barry. I'm glad the video was helpful.
Thanks again Doug....fantastic video, and thorough explanation. And thank rusty as well.
You're welcome, Bryan. Rusty and I send our regards and sincerely appreciate your time and interest :) ^. .^
Thanks for posting this. I've always enjoyed the sound of tube amps, and tinkering with electronics. Recently, I've been itching to building my own tube amp (but I don't play guitar ... weird, I know). Before I pull out the soldering iron, I want to understand more about what is actually happening inside the amp. It looks like I'll be spending a bit of time on your channel in the coming days.
You're welcome, Jon. Hopefully the videos I have posted will give you a basic understanding of amplifier circuitry. Best of luck with your pursuit of knowledge.....and your project.
Dirty uncle Doug! Thanks for the video. MY kx15 crate amp was buzzing really loud, and there was something loose inside.I resodered the loose part, but I forgot which wires went where... now trying to learn a lot.thanks again, peace
+alex thefakest You're welcome, Alex. It's good that you are trying to learn as much as possible to enable the repair of your own amps. That's always the best place to start. Best of luck with your project :)
Always take a photo before dismantling a circuit.
Hi, Unclr Doug, here's a good one.
I'm rebuilding a Newcomb AV-7 phonograph with a Widow Maker circuit. It has a a 12av6, with dual diode and a triode in the same glass envelope. The diodes are connected in a half-wave configuration, and a solid state diode is connected in the heater section. I've seen a similar circuit using a single diode tube, and a SS diode in the heater section.
I tend to avoid the series-filament circuits, Stephen, but this one sounds rather unusual. Thanks for sharing it with us.
@@UncleDoug Thanks for all of the Videos, and for your reply. After weeks of study, and searching for an isolation transformer that never existed, I tend to concur. Current draw on a 'Widow Maker' is enormous. But it was a great case study in archaic engineering (and finding obsolete parts), and I did find an excellent source for schematics:
''Practical Amplifier Diagrams'' (Robin & Lippman, 1947).
You, and your fan base, can download a PDF copy for free.
Best explanation I’ve ever seen. Bravo. Thank you!!!
You're welcome, Michael. Thanks !!
Wow. I'm amazed and informed with every video!
Glad to hear it, Ed :)
This is a superb explanation! Really made everything simple and easy to understand : )
Thanks, Zach.....glad it was helpful :)
Another great video. Great explaination and teaching style, thanks so much!
Thanks, Scott.
You sir are an excellent teacher!
Thanks Ben :)
Thanks for all your time in the information we definitely appreciate it
You're welcome, Robert
Really great video. You made this very easy to understand.
Thanks, Don :)
Great work Uncle Doug!! Best subscription I've done EVER in YT!
I'm hungry for knowledge, keep those awesome vids coming!
Greetings from Greece!
Wow....Thanks, Foibster. Rusty and I really appreciate your kind words of support, and hope that all is well in Greece !! :) ^. .^
A very thorough explanation, thank you. After running some simulations in LTSpice, I completely understand your preference for the soft start of the GZ34.
Thanks so much, BT. I'm glad that the GZ34 distinguished itself.....it's a great rectifier.
very informative and appreciated, you are a good teacher. thank you
Kevin Courtney Thanks, Kevin. I'm glad the videos are helpful.
Doug, this is a great explanation, best I've seen yet. If you get a chance to make another video, could you please go further into depth on tube rectifiers and how is it that we get the B+ off of the cathode. Also, how does the current flow through the anodes since it appears to be a seemingly open circuit. I'm assuming the anodes don't touch.
Please check our more recent videos on rectification and power supplies, Maddox. They contain the information you seek.
Thank you Sir, don't stop doing the good work you do!
uncle doug you kick ass. thanks!
John Brown You're welcome, John :)
there are many great videos here that help tremendously. But what about repairs and identifying distortion and other enomolies in existing new and vintage amps?
I have posted quite a few videos demonstrating diagnostic and repair techniques, Francis. Please check out my video list.
I'm working my way through all your videos UD&R. You are hitting on all the topics I have questions about. It's like you're reading my mind. I understand the electronics from a numbers side, but never understood why "filter caps" were in audio circuits. This video filled in some big gaps for me. THANKS!
You're welcome, Greg. I try to cover all the topics that puzzled me when I started out with tube amps.....and, apparently these topics coincide with other people's areas of uncertainty. Rusty and I are glad the videos are helpful :)
Uncle Doug, I have a few questions for you and please explain them :
1. What is 169VDC RMS !!!!?
2. What is pulsating D.C.?
3. If I need +270VDC, using a two-diode full-wave rectifier, how many volts should the transformer secondary be?
4. What is the P.I.V. of a diode?
5. What is 120Hz hum!!!!?
6. Why is a computer power supply so special that deserves a mention?
Looking forward to hearing from you, Uncle Doug.
Paul Cheung
I started to answer all of these, but realized that the answers are all readily available either in my videos or via internet searches. Good luck.
Thanks Uncle Doug!
You have a eliminated so much of my ripple lol
GREAT VIDEO LESSON!!! (I will be watching this repeatedly)
Rob Valdivia You're welcome, Rob. I'm glad that Rusty and I could smooth out your B+ :) Thanks for the kind words and best of luck.
Thanks so much. Explained so well!
Thanks, Kevin. I'm glad the video was helpful.
Such a beautiful explanation.
Thanks, Christoph.....I really appreciate your kind assessment. I have several other technical videos that may be of interest. Please check my most recent posting on Output Tube Biasing.
Super explanation! Thank you for posting.
Glad you enjoyed it, WW :)
Thanks Doug! Your videos are excellent
You're welcome, PDE.
keep it up Doug. I am learning so much .Thank You.
I will, Edwin. Thanks for watching !!!
Great info, thank you. I am trying to fix a home audio amplifier and was hoping you could help me troubleshoot it. The bridge rectifier on the power supply board emits a large spark when I power it up though it continues to work. I replaced the bridge rectifier and 2 small caps next to it and the problem remains!
Since bridge rectifiers are generally sealed blocks, I'm not sure where the sparks could be coming from, MT, but it sounds like the start-up voltage spike exceeds the rating of the BR. If the BR worked fine for a long time and suddenly began to act up, perhaps your filter capacitors are drawing more current than they should. You need to evaluate this before sacrificing another BR. It may be time to change the filter caps.
Are the filter caps the large ones (6800uF 80WV)? The spark seems to originate at the + lead of the bridge. You can see photos and video at this forum post: forum.allaboutcircuits.com/threads/home-audio-amplifier-repair.128825/
turned out to be a bad solder joint at the smaller "in-line" rectifier on the board. Working great again!
I've watched this before..its Good to refresh my memory..
Repetition is good for recall. Thanks for watching.....twice :)
Hi Uncle Doug, thanks for your comments recently on the output transformer video, where I was asking about an old amp I am fixing up. I have a speaker I am going to get out of storage to test it with. In the meantime I have taken the back off and started to map out the circuit and compare it to the champ / vibro-champ schematics. There is something strange about the filter caps - or maybe I should say lack of filter caps. There are two cans on top of the chassis, one marked 8 + 8 uf and one 20 uf, but having looked inside there is effectively a jumper across the first, and the second is not across the rectifier output but along the + rail, with a 400 ohm resistor across the terminals. Will it still function as a filter cap connected like that? I suppose the other cap might have failed and someone might have thought it wasn't worth the cost of replacing it, but I didn't think they were that expensive - would there have been any other reason to take it out of the circuit?
As I say I haven't put it through a speaker yet but I am guessing there will be a good dose of hum when I do.
You're welcome, WS. Without seeing the components in person and having a schematic, it's just about impossible to make educated guesses. I think you need to map out the entire schematic, as you mentioned, and then see for yourself if vital components are missing, bypassed, or inoperable. It sounds like there are some problems with the filter caps, and you would probably be better off simply replacing them with new ones (they aren't particularly expensive). This is a dangerous part of the circuit, so be very careful. Do not plug it in or test it without running it through a current limiter (see my video). It will greatly reduce the chances of damage. Good luck.
Great video, very concise. Thank you so much Uncle Doug for posting. Subscribed.
You're welcome, Rudy, and thanks for the kind words. Welcome aboard :)
Way less rippled! Thanks a lot.
Yago Bolívar You're welcome, Yago :)
Awesome. Excellent presentation. Thank you.
You're welcome, Joe.
Absolutely brilliant explanation, thanks for the video!
You're welcome, WW. Thanks for the nice comment :)
that 5u4 looks just like my 5z3p- cool, man i am hooked, long live the tube!!!!
+jeff b The two tubes are quite similar in design, but have different numbers of pins and different pin-to-component internal connections, Jeff. The 5Z3 was a popular rectifier with early jukebox amplifiers.
cool, did not know that, using the 5z3p in the Hifi with 2- 6N9P'S and 2-EL34-B'S, going to correct all my mistakes after watching some more of your videos 2 or 3 more times as to absorb all the info, happy holidays to you and rusty- sorry forgot your cat's name him too, take care
Happy holidays to you too, Jeff, and best of luck with all your projects in the new year :)
thank you, you are a class act my friend
You're welcome :)
I always knew what filter caps did, now I know how they do it!
I'm glad the video was informative, James.
Uncle Doug - I watched a video where the guy describes the filter caps on the 5F1 as being “underrated for the circuit.” He mentioned that his preference for the filter caps is: 33, 22 and 10 respectively, all rated at 450v- to eliminate hum. But my mind always says there will be some type of trade-off when deviating from the schematic - some good, some bad, and within those values there are all kinds of electrolytic caps, size, tolerances, etc. It’s a jungle out there. In the old 5F1 circuit, and taking into consideration modern voltage at the wall, is it preferable to increase the values of the filter caps, and if so, what’s the trade off’s of doing so? Thanks!
First off, there is no need to increase the values, Chad. A properly built 5F1 will have no hum issues with the original cap values. The downside to wholesale cap enlargement is that the capacitors represent a virtual dead short to the circuit when it is first turned on (to charge the filter caps). When you grossly exceed the design parameters of the circuit, damage can occur to the rectifier tube and possibly the high voltage winding of the PT.
@@UncleDoug Thank YOU!
Two years ago, I shopped for a Supro amp. I listened to the Thunderbolt MKII and Thunderbolt+ and found a tremendous difference in their sound, the plus model sounding much better to my ears. Supro support explained that the only difference between the two circuits is that the plus uses a tube rectifier, whereas the MKII uses a solid state rectifier. Does the type of rectifier that's employed generally contribute significantly to an amp's tone? If so, why?
Tube rectification is usually limited to sub-50W amps, Dave. To get 100W usually requires two rectifier tubes, as in some Mesa amps and an unusual model of the Fender Bassman 100.....while diode rectification can easily exceed 100W. Thus, it's apparent that current flow is limited with tube rectification. While this sounds like a detriment, many people, including yourself apparently, prefer the tone created by the "sag" or delay in current flow within the output tubes found with tube rectification.
@@UncleDougthanks for that additional information. As others have said many times, you are a uniquely talented teacher. The difference in sound between the two amps I mentioned was remarkable. The plus amp brought my Telecaster to life. The MKII sounded similar to the Thunderbolt+ through a Koch Dummybox--dull and lifeless.
Then in your case, the choice of amp seems quite clear, Dave.@@DaveCorsello
Another excellent video but how do you choose the resistance and capacitance of each node in order to get the correct voltages? Also how do you calculate the use of a choke? This is probably the main issue I have design. At the moment I just look at what Fender/Marshall etc have done and copy then tweak their design but it would be nice to be able to calculate the values of the components myself. Thanks. So for example I'm building a stereo amp based on a circuit similar to the 5F1 but using a beefier power supply, a James tone stack and 3 stages plus a GZ34. How do I know the capacitors and resistors for each node? My current plan is the steal the values from the Deluxe or Princeton Reverb!
Using data from existing, successful circuits is a good, easy way to get ballpark values for the components in your circuit. You can then fine tune the values as needed. If you wish to start from scratch, you will have to know the current flow through the power supply rail and then calculate the voltage drops necessary for each amplification stage. The trick is knowing the current flow......which requires some guesswork, and results again in ballpark figures that have to be fine tuned. There are no absolutes, only educated preliminary guesses, and subsequent adjustment to suit the circuit. Good luck.
Thank you. It looks like I will need to discuss this further with Mr Kirchhoff and Mr Ohm :-)
@@cowasakiElectronics Be sure to take a shovel with you for the meeting ;)
Hello Doug, I have been studying the Vox AC10 schematic as it is a simple 10W tube amp to learn the basics. I note that the PT puts out 300-0-300 to a 6CA4. The +ve output from this tube is 320V. This is subsequently stepped down through a 5 Henries choke to 305 and 255V for the 12AX7 and two EL34's; plus an EF86 and ECF82 respectively. What I dont quite understand is why the 300V input to the rectifier tube, (6CA4) increases to 320V. This is an increase of 6.667%. How do you account for this increase and is there a way to calculate what it might be for other voltage inputs. Why I ask is that this type of PT 300-0-300, 6.3 120mA are hard to come by. If I used a different PT with say 660V total output could I still achieve the required B+ V of +305 and +255 by using a different choke, or preferably a combination of resistors?
allanpennington Greetings, Allan. This is a complex issue. The problem is that AC is measured in RMS voltage, and DC is not. The 600VAC output from the power transformer secondary is equivalent to 600VAC divided by 1.414 = 424VDC . This number is then reduced during rectification, filtration, and choke coil to the +320VDC you cited. If you used a 660VAC PT, the value would be about +350 to +360VDC. This added to the increased wall voltage we now have (compared to when these amps were built) could yield a rather high plate voltage value for the EL34's, which prefer values closer to +320VDC. You may be able to lower this using resistors (which also reduce the plate current and get hot).....but the best bet is to use a proper PT. See Triode Electronics for good PT's at very reasonable prices. Good luck.
Uncle Doug Thanks Doug for getting back to me. I am in New Zealand so shipping PT from the States is an expensive proposition. There is a UK company who make an exact AC10 PT clone which might be an option. We are also on 240V AC house current here so this adds to the complexity when looking at old circuits although I do have a 240 to 120 step down transformer I got years ago when I purchased the first Apple Mac Plus on the way home through the States from England to NZ. I have never had a tube amp and they are so expensive I thought I would give making one a go and I like the tone of the Vox AC10 SRT which was put out in limited numbers. The SRT had a separate two speaker cab and the head had reverb as well. Maybe something simpler to start might be the best bet. Thanks again. I really enjoy your MOI. Thats Army slang for Method of Instruction.
Great explanation Uncle Doug! Thanks.... And as I like to joke abit, back in the day I had a bad bottle of "Ripple" and the next morning my head had a very large hum!! Ok, ok. I'll stop! Seriously though, Ive learned alot from you and greatly appreciated it!!🎼🎛
Ripple was the nectar of the gods back in the old hippy 60's, Wayne. I downed many a bottle of it while listening to Iron Butterfly and Vanilla Fudge albums ;)
@@UncleDoug Remember it well!!! Matuse White...
Thanks incle doug i have vlearnrd so mich from uour wealth of knowledge 😊
I'm glad to hear that :)
Thanks Uncle Doug! Well done!
You're welcome, T :)
Thinking of trying to scratch-build a 6G6B Bassman, in which there are six diodes in a full wave rectifier. Unfortunately, the schematic doesn't say anything else about them. I've found references to what diodes to use, but I'm wondering now if it would be possible to use a "pre-fab" bridge rectifier, instead, and if so, what I should know about the unit.
Stick with 6 individual diodes just like Leo did. You can order them from Antique Electronic Supply for about $2 (total.....not each). Their part number is P-Q1N5408 1000V 3A rating @ a whopping $.35 each.
Thanks! You're the best!\
You're welcome, Ed.
Very Good explanation. Tank you very much.
You're welcome, Nelson.
This is a great video! Thank you for your explanation.
+Michael Martinez Thanks, Michael. I'm glad you liked it :)
Is there any way to strap on two diodes to an existing tube rectifier to create the four-way bridge rectifier?
Possibly, but it would not be a good idea since the high voltage primary winding is either suitable for FW or FWB rectification, but not for both.
In videos I've watched the value of the filter caps is often greater than the original spec. Can I assume the value just needs to be enough to always have enough capacity to fill the ripple? Would substituting, say, 100uf cap instead of a called for 8uf be fine to use aside from being overkill and expensive?
Thank you, Uncle Doug!
You need adequate capacitance to fill the ripple, as you said, but going too high will stress the rectifier tube on start-up, since big caps draw a lot of current to initially charge up.
What a great YT channel
Thanks, P.
Thanks for the video.
I just purchased a Panama Conqueror which is a Champ copy. The rectifier is a 6Z4 Chinese tube. Is there a US version of this? Or, is it easy to replace that tube socket with one of the tubes that you prefer?
The Panama uses a 12ax7 and a 6v6GT tube compliment.
Or, is the 6z4 good enough to keep and not worry about?
Thanks for any advice.
I am not familiar with 6Z4 rectifiers, Mozilla. Try it and see......it may work just fine. If not, then conversion to a 5Y3 should help.
So the 5v ac heater windings also provide the cathode output (B+) and like a small ac signal voltage can co exist with a high dc voltage in the same conductor then this is the same principle. Have I got this correct?
+Barry Davison The final statement is correct.....AC and DC can coexist in the same conductor. The 5VAC heater winding doesn't provide anything but excitation to the cathode, which makes the rectifier work. The DC B+ that is produced by the rectifier simply exits via the 5VAC wire.
Another great video. Thanks!
You're welcome, James.
very cool video, thanks uncle
Thanks so much for these videos Uncle Doug. I'm hoping to get a better understanding of how to select the capacitance of the Filter caps when using rectifier tubes. Is there any chance you have any videos that talk about that? I've been told that you need to be concerned about the in-rush current because the Rectifier tubes can't handle too high and that's why the capacitance needs to be low. I can't say that I understand why higher capacitance would increase that current (but I am just learning).
When an amp circuit is first energized, the filter caps have to charge up, so for a second or two, they are like a dead short....the higher the capacitance, the longer the short lasts. The maximum value for 1st filter cap is given for each rectifier tube in tube handbook(s).
@@UncleDoug That makes sense. Thank you. I'm reading Megantz's book and he mentions that the final stage of filtering is the preamp section and that is because you want to filter it more. So is there a reason that we usually see all low capacitance caps in a row? Why not just the first cap low and then all the rest higher?
would there be any improvement in using 4 diodes total (2 on each output wire) for the full wave rectifier?
Fender uses six diodes, Dave, three on each wire, so from a practical standpoint, i.e. protection from the failure of one or two diodes, it must make good sense.
Are you saying that we cannot hear or detect the negative side of a 60 Cycle sine wave? I have always thought that the humm coming out of my Vox AMP was the sum of one full wave, above and below the null line.
Since the AC is rectified in an amp circuit so that only the positive wave forms are sent to the amplification circuit, there are no negative wave forms to hear. Look at the ripple in the output from the rectifier (in my diagram). It's a small fraction of the total amplitude of the original AC, but it will still cause the speaker to move in and outward at 120Hz, providing the hum associated with failed/failing filter caps. The caps smooth the ripple, charging the DC up to peak voltage and providing a smooth, silent, unrippled DC power source for the pre-amp tubes.
Extremely Useful information!......Uncle Doug for a 5C3 circuit....5Y3GT...would a 5V4 be better? I realized of the slow warm up but if compatible...will it change the sound color or attack of the amp sound/tone signature?
atta1798 Greetings and thanks, Atta. Replacement of the 5Y3 with a 5V4 is a favorable exchange and is said to offer a little more headroom, greater volume, tighter bass, and the tube-saving advantage of slow start up.
Uncle Doug thank you!....
I have a peavey tnt 160 bass amp with a "120 Hz" hum. if I bang the top of the amp with my fist, the hum almost disappears but can come back over time. I am wondering, does that mean there could be a bad solder joint between the capacitor and the circuit board or is it just an old dried out filter capacitor due to the age of the amp circa 1985. This is a great amp and it would be a very satisfying exercise if I could fix it. I am thinking if I can put the guts on the bench and wiggle the caps, that might give me a clue to whether the connections to the board are sound? Opinions? Thank you, your videos are awesome.
Kevin Courtney Thanks for the kind words, Kevin. The only source I know of for 120Hz hum is faulty electrolytic filter caps. The fact that the hum subsides when you vibrate the amp might indicate a faulty solder joint on one or more of the caps. If you can wiggle the cap and its connections (with a wooden or plastic stick....not a pencil) you might be able to determine which one is at fault. While you're at it, wiggle the tubes, especially the rectifier (if it has a tube rectifier). Whether or not you can find the culprit, it wouldn't hurt to replace the filter caps. Good luck.
Have a question. How to choose a rectifier tube for the scheme? Indirect heating for the slower warm up - done. But all other parameters? Heater current(HC). Peak inverse voltage(PIV). Max rectified current(mRC). Plate current. What they should be?
I'm choosing between GZ30 = 2A (HC), 125mA (mRC), 1400V (PIV) and other tube with 3A (HC), 190mA (mRC) and 1700V (PIV).
You said you like GZ34 the most. Why? I can see that it can output more current. has less heater current and has average PIV in comparison to the above mentioned. Are these critical parameters?
Thank you.
Best regards,
Yury.
Good question, Yury. I would say that an ideal rectifier should exceed circuit requirements by a "comfortable margin". If total voltage and current requirements (either directly measured or accurately calculated) were 90mA and 350VDC B+, then the GZ30 would be a good choice, and it's lower heater current would be less burden on the PT. If the V & C requirements were 115mA and 475VDC B+, then I would probably go with the 3A tube. I personally have no exact formula, but simply rely on common sense. In most sub-30W amp circuits, the efficiency, slow startup, and low PT demands of the GZ34 make it an obvious choice....at least to me.
I have a question about filter caps in general. Is it possible to hear difference between filtercaps from different brands with the same value? I have a Marshall jmp 50w amp that uses 3 x 50+50 500V caps and they need to be replaced because they sit in there for 35 years.... I see a lots of brands with different prince tags on them so I wondered they smooth out the ripple so there should not habe been any difference?
+Marco Hermans Marco, are you changing the filter capacitors because they are old....or because they are not functioning properly? If they are working well, I would leave the old ones installed. Personally, I don't think there is any difference in tone or function between electrolytics which are expensive and those which are reasonably priced. Sprague is a good brand, and I've had good luck with Nichicon and the black, German caps (name eludes me). Don't get the cheapest or most expensive caps.....go with the ones that are reasonable and somewhere in the middle.
They've bulbs on two of them so replacement is more of a safety issue to me. I hear a sort of 100 Hz noise when I crank the master volume past 5. (We have 220V ,50Hz in Holland) This is the first time that I'm gonna service an amp myself . At technical school we learned a lot about electronics 30 years ago about transistor amps and not about tube amps (High voltage )That's why I watch all of your video's and learn as much as I can before I'll give it a try. I figured out that buying some decent alligator clips is not a waste of money...Safety first...
Safety first indeed, Marco....be sure the clips are well insulated. It does sound like the filter caps are failing. You might want to make a cap-draining probe. I used an old phillips screwdriver, sharpened the tip, and connected one end of a 100 ohm 10W resistor to the metal shaft and the other end to a grounding wire and alligator clip. Connect the clip to ground and touch each + cap lug for a few seconds. Observe cap polarity (almost always neg to ground) and be careful. Best of luck.
Thanks for the tip . The next step is to check the first pre-amp tube (ECC83) because my amp have two inputs, high and low. Each input goes to one site of the ECC83. The low input doesn't function anymore and the high input does function normally. Clean the sockets.When the amp is serviced I'll make a schematic with voltage measurements on crucial points because I can't find one for the JMP 2104 with EL34 power tubes on internet. Because I wanna keep that amp forever I'll put new tolex and grillcloth on it because that's have been worn out. Your video's teach me everything I need. I'll let you know how it works out.
Please do, Marco. Best of luck with your project :)
I have a question and sorry if my english is not good. Can you replace the 5Y3 of the Champ Amp by some tube with cathode?, ¿What happens if I connect the cathode of the new tube only to the "+B" of the circuit and the heater only to the yellow wires? Thank you!
Juan, about the only rectifier with a cathode that you could safely substitute for the 5Y3 would be a 5V4. You would not change the socket wiring at all. Your plate voltage may go up a little so you would have to check it. The high voltage goes only to the plates of the rectifier, never the cathode. The rectifier creates the B+ (rectified high voltage). If I were you, I would stick with the 5Y3. It's a great rectifier for the Champ.
Excellent - helped me a lot!
Thanks, Lorne. I'm glad :)
Very well done!
Thanks, BB :)
very usefull video! thanks Uncle Doug
You're welcome, El :)
strange amp: 3 Power Tubes? ... I'm not sure how to contact you with an only partly related question so am picking this video that seems at least in the 'how to' range of topics. I have a small 1950s/1960s Filmworks projector amp (volume and tone controls, one input-microphone, otherwise the amp would amplify the film audio) I am going to clean this up and use for guitar and I'm confused about the tubes. The larger tubes are a rectifier (5Y3GT), and then there are THREE 6V6s. That doesn't make sense to me to have an odd number greater than one. Could it somehow giving the mic a power section with one tube and the film audio a separate power section of two tubes? That seems unlikely but I can't think of what else it would be. If you can think of anything that might explain this, without thinking about it too hard, I would be interested to know. I haven't opened it up yet, but am interested in your thoughts.
I have never heard of an amp with 3 output tubes, OM. See if you can find a schematic for it and post it on my Facebook page: Uncle Doug's Vintage Amps. Maybe we can figure this out.