Genius again. I started sending people to your channel rather than continuing to try and get them to provide accurate information instead of folklore to their subscribers. You make a clear, simple and non-mathematical case for why actual knowledge and experience are important. RUclips is stuffed full of people whose only sorce of information is RUclips itself. It is a viscious, circular race to the bottom. I watched a whole series wherein a guy utterly destroyed an irreplacable, priceless old receiver by putting bigger, better looking caps in and correcting the manufacturing defects where Pioneer had left out key parts. Of course, the PCB was used for several products. Nothing was left out. Now, the old machine has several corrected circuits and better caps - but next time, he will use even bigger caps because he still doesn't think it's right. GROAN! There is no way to fix the RUclips problem. All we can do is point people in the right direction. I am so glad people like you take the time to produce real content. I am sorry about the spelling. I am writing on a phone while riding a train. You can understand what I mean.
Thank you for the insights and tour of your workspace. I service Fender, Hiwatt, Marshall, and various tube guitar amps for myself and other local musicians in my area. Your videos are very informative and help me apply what I learned years ago and did not fully use until this later stage in my journey. Two thumbs up!
The purpose of the grid stopper resistor is to improve the stability of the amplifier by reducing the possibility of high frequency self oscillation. This works because of the resistance of the grid stopper reacting with the capacities on the grid of the vacuum tube forming an RC lowpass filter network.
Those "spurs" look like IM Distortion. Specifically, the 60Hz & 120Hz power supply noises modulated onto the fundamental as well as each of it's upper harmonics. Using a regulated DC voltage or current supply for the filament may greatly reduce this effect (since these are direct heated triodes).
Gary Trautman Another way to look at it would be as AM sidebands. The heater AC is amplitude-modulating the 1KHz sine wave carrier. When you balance the heater AC properly in a PP output stage it cancels out inside the output transformer,as does the hum.
Dc supplies significantly lower the life of the filament due to cathode posioning ac supply is fine if it's done right. just cause u can measure it don't mean u can hear it if u can't hear it it don't exsist. Maybe u could do DC on preamp tubes like some new production tubes u don't care about or u could just use tubes made to minimize hum 6eu7 shielded 6cg7 with cross talk speperator comes to mind perhaps some tube shields. But I would never never ever put DC on expensive output tubes cause actually it's useless power tube have some much ps rejection since they sink current and not voltage and not to mention it shortens there life. so there is my two cents
Dave, What grid "stoppers" stop is parasitic oscillation. The higher the gm of the tube, the more vulnerable to parasitic oscillation it is. It is a rule of thumb among DIYers to assume parasitic oscillation will be present and install the stoppers, from the very beginning. As gm goes up, so should the stopper value. For instance, I call for 100 Ω on 12AX7 grids and 1.5 Kohms on 6922 grids. I strongly prefer carbon comp. parts as "stoppers", given they are both non-metallic and non-inductive. Speaking of carbon comp. parts, when dealing with "ancient" NOS, bake them in the kitchen oven, to drive off absorbed atmospheric moisture, before taking measurements. You will see in some schematics very large valued "stoppers" on the O/P tube grids. Those parts are doing double duty. Aside from parasitic oscillation, they also help in "taming" blocking distortion. Eli D.
Hi Eli, I know your comment is a year old and for reasons I don't always understand, I don't see comments in a timely manner when you guys reply. Anyway, I really appreciate your advice and I do nowadays use grid stoppers. I think I have learned from you guys and you did a great job of explaining it and the reasons for using "stoppers". I have even recently taken that a bit further and use stoppers or maybe call them isolation resistors, in the screens and even the plates of parallel push-pull amplifiers like a quad 1625 modulator I recently built. By installing 47 ohm resistors in the plate leads and 100 ohm resistors on each screen (if my memory serves me at the moment) it completely stabilized and otherwise very unstable amplifier. Just did magic for it. Thanks again. Stay safe.
I'm desperately looking for resource to find out what some of my vacuum tubed equipment is , one looks like a time machine and and old tubed IBM computer something or another and I just might be curious enough to plug this in one day , so for possibly the sake of humanity, please help me find a resource
Great video. Very helpful. I've built a number of tube guitar amps now and am really enjoying them. I'm interested in trying a hifi amp. I currently have a pair of Overnight Sensation desktop speakers with 25 watt drivers that I use with an old solid state receiver. I'd like to built a tube hifi amp to replace that receiver. I'd just be listening to music in my study. Not terribly loud. Any suggestions on circuits I could look at for inspiration?
For some really good ideas take a look at these files. There are four parts, www.google.com/search?q=100+amplifiers+part+2&rlz=1C1CHBF_enUS757US757&oq=100+amplifiers&aqs=chrome.3.69i57j0l5.7555j0j8&sourceid=chrome&ie=UTF-8 You can find them all by Googling, "100 Amplifiers - Part 3", etc . I personally would use a 6L6 as an output tube (also known as a KT66) and a Williamson design. The Heathkit W5M is a good one and there is a little bit older design with 6SN7's that is my favorite . www.mcmlv.org/Archive/HiFi/HeathkitW5M.pdf I like vintage Acrosound transformers or new James Audio transformers for the output. www.tubebooks.org/file_downloads/acrosound.pdf These amplifiers are in the 20 watt range which is plenty for efficient speakers.
Hi, Id like to know if its important to have the right filament voltage ,cause i made an single end kt66 and the power transformer give me 7 v unladen and 6.8 v loaded ,i see on the forum the guys says life tube is longer with 6.3 v exactly ,so regulation on filaments may be a solution ,what do you think about!
Usually, filament voltages do measure 7 volts or more at the transformer terminals when unloaded. That is normal. It is better to have filament voltage a bit high than low. I had some foreign made 300B that when run at 5.0 volts on the filaments, would not perform. I had to raise the filament voltage to around 6 volts to get the tubes to perform correctly. Obviously, a QC problem with the tubes. People worry way too much about how long their tubes are going to last. I had rather run my tubes with a higher filament voltage and have good performance than have them run poorly or marginally at some text book level or what some forum says. Your 6.8V is perfectly OK at the filament pins, and then move on to the rest of the design and build of the amplifier.
Grid stopper Resistors along with the capacitance of the Tube form a low pass filter, Thus providing frequency compensation, In addition this Resistor provides a Real Impedance for situations where the Grid turns Inductive and can result in a negative Impedance. Grid stopper resistors are also used with Transistors, however are called Base stopper Resistors.
Thanks, Philip. It took me quite a while to be convinced that they had a real value but I am convinced now. The most dramatic situation I had was a McIntosh amplifier build that I have shown a number of times on YT where when the input gain pot was almost all the way down (lease amount of input) the amplifier would often times go into a parasitic. It puzzled me as I knew it was a good design but the issue was finally explained to me much like you just described it. I am a believer now. Thanks for your comment.
With the direct heated rectifier tubes like the 5U4 and 5Y3, the DC comes on strong in just a few seconds. 5AR4 and 5V4 take a little longer to heat up so maybe they are all a little less stressful on the electrolytic's in the PS as it gives a few more seconds for the other tubes to warm up and load the PS.
Once again a great and informative video well done 👍 The voltage measurement on startup and capacitors ratings getting over could be some nice new video if you didn't do it already (?) last but not least I believe you Feed that focusrite soundcard on the mic input, so unless there's a mic/line switch available on the software that's why you need to attenuate the input like that.
The next video is already in my head. I know the LTSpice videos are not the most popular but to see the way different values for chokes and capacitors perform in a Pi network in a power supply might be a real "eye opener". As for the Focusrite, I do keep it in the line position (it has a switch) and it will take 5 VRMS input with the gain on the sound card at the 12 o'clock position and remain green so it's not too hard to keep the drive down.
Question? What device uses two OD3a tubes with a large transformer and a huge cap ? Is it a power supply ? I bought this thing off an estate sale and for 20 bucks and it seems to work. From what I understand, the OD3a tubes are pretty expensive. If so, what is this for ?
I have that same triplette meter in the background. The ohm scale dosen't work anymore and I'm guessing its a battery. Do you know what kind of batteries they use?
BurningTirez It is usually a 1.5V D cell. Many people remove it and put in a 1.5VDC supply powered by the heater AC. You can do it with a capacitor and three diodes, one to1/2-wave rectify and two in series as a shunt regulator. I am about to do it with a diode, a capacitor, an LM317, and two programming resistors, which will waste a lot less heater current. You don't want to be fiddling around with batteries in this day and age, even though in a VTVM they will last a decade or so.
BTW, I've found that the film capacitor used for DC Link Bus and IGBT Snubber applications are far superior for noise rejection. It's actually hard to determine which terminal is connected to the outer foil.
Hi Gary, I actually don't know what you are talking about, I just understood the last sentence.I was going to say that Mr Carlson's Lab has a video on figuring out which lead is the outer foil. I just marked out about 40 caps last night using the oscilloscope. As I don't use enough caps for the hobby, I didn't build the unit he build's in the video (don't know if I could), just used the scope as he shows.
Sounds like you do know ;-) Finding the outside foil of the typical cylindrically wound film capacitor is very easy - the outside foil can't reject noise. The various DC Link & IGBT Snubber Caps that I have tested are not nearly as sensitive - Carlson's method will fail to identify the outer foil reliably. Not sure how these caps are constructed, but something is definitely different. They are also epoxy encapsulated & very well constructed, eliminating the microphonics most film caps suffer from.
David, are we going to see an attempted repair of the Mcintosh Receiver? I for one would enjoy it. I enjoyed this video as well. Always like to hear your opinions on things... Take care, Tom
Hi Tom, Well, now that you have mentioned it, I guess I have no excuse not to try. I hadn't seriously thought about it but I do have a schematic of it and the test equipment. I just really don't like working on SS equipment. This would be like going back to work... I would have to work quickly as in about 10 minutes it settles down and works fine. This particular receiver/preamp has a lot of noise in the tuning process. It always has had that issue and in the past I have run the tuning dial from one end to the other a couple of times and it quietens down as it is tuned up and down the band but I don't remember the volume going up and down in the past just sitting on one station. I have had this unit 20 years or more. It is old style tuning with a variable capacitor. I suppose it could help others with this issue if I can find a real fix for it. I will give it serious consideration. Thanks for your comment.
I put the MX112 on the bench and took the covers off, etc. ready to figure it out and it worked great. No issues. I guess it was just bad connections/cables between the tuner and the amp. I did change out the cables.
That's good news. It would have been interesting to see you diagnose/repair a problem on the receiver if there was one, but I'm glad for you that there isn't.
An electric guitar amp is an instrument itself. That's why some prefer a tube rectifier or a silicon diode rectifier, depending on musical style and role in the mix.
I have made a few 2.4 GHz antenna videos and one video for log periodic antennas that I made and use for TV and FM stereo reception. The only antenna I have up right now for HF is an aluminum tubing rotating dipole for 20M. Years a go I was into yagi antennas (VHF and HF) with gamma capacitor feed and that was a lot of fun but nowadays I just operate 20M. I am very much a believer in the use of the so called, "choke balun" as it works great for me. Simple to make and cheap. However, these chokes must be built for each band as a single one will not work for the whole HF band.
I'm preparing to build a 6B4 stereo amp. You've given me a lot to think about. SS rectification vs. tube. Was planning on parallel 12AX7 drivers, now I'm not sure. I've heard that 2A3/6B4 types need a high mu tube and I've seen both 6SN7 & 6SL7. So confused! Ground buss wire or star ground?
I will try to tell you what I think about it. First off, we do not need power to drive the 6B4G triode. We need voltage. They run class-A so they need no grid current. Typical RC coupled stages deliver around 50 volts drive and the 6B4G runs around -45 bias at 250 volts on the plate. So RC coupling should be OK. I assume you will get your bias by way of cathode resistor and bypass capacitor. What this leads up to is if one wants more voltage drive for the grids of the output tubes, it can be solved with a choke, sometimes known as impedance drive. The chokes are available and are expensive and are around 2500 H. Study this schematic and see that Altec drives push pull 813 to 260 watts with a 6AU6 and the impedance choke www.vintagewindings.com/gen%20pop/8299543VW8335/Altec/Altec-260A.pdf The 6SL7 is a high mu triode just like the 12AX7 and the 6SN7 is a medium mu triode just like the 12AU7. Assuming you want around 1.5 volts input to drive your amplifier to full output, you only need a medium mu triode. I generally avoid the 6SL7 as it has so much gain only 100 mV or so will drive the amplifier to full output and it is very easy to overload the input to the amplifier. Acrosound published some beautiful schematics back in their day. I recommend using their design. As some on the Internet do, "let's try this and let's try that and see what happens" usually leads to a poorly performing amplifier. SS or vacuum tube rectifiers are just a choice. The rectifier tube is pretty so people still use them. Here is the Acrsound catalog with schematics. www.tubebooks.org/file_downloads/acrosound.pdf In my opinion, one of the best simple Williamson amplifiers ever built is the Heathkit. Here is one version with 12AU7's and KT66's (you can use your 6B4G's in place of the KT66's). I assume you know 6B4G's have a directly heated cathode and require a pot of 5 watts or better around 25 to 100 ohms for a cathode return to ground and hum adjustment as the indirectly more modern tubes do not. www.ampslab.com/vintage_heathkit_w5m.htm Here is the Heathkit with 6SN7's (my favorite) www.nostalgickitscentral.com/heath/schematics/heathkit_schema_w4am.pdf Lastly, here are some more schematics (there are five books like this. Just change the part-3 to part 1 thru 5 lilienthalengineering.com/100-amplifiers-chapter-1/100-amplifiers-part-3 I almost forgot the grounding - ground all of your power supply components (CT of transformer, electrolytic capacitors, etc to a single point on the chassis). I have found the complicated star and buss grounds unnecessary and messy. You can ground cathodes and inputs right to the chassis. Study the grounding scheme of a McIntosh amplifier and you will see how the real pros do it. Hope this helps.
Thanks for the quick response! If I knew you'd write such an informative response I would have been more accurate. I'm actually planning a DC Loftin-White inspired 6B4G. Originally I was thinking SE EL43 or 6L6 but I've already built one (super great amp...just so many yet to build and experience). Never heard a SE DHT though, and I've heard...there ought to be a law that EVERYONE has to experience a DHT at some point. Already have a pair of Russian 6B4's on the way. I think I've narrowed it down to a couple circuits. www3.sympatico.ca/wenchieh/2A3_schematics/shishido.jpg 12AX7 in parallel www.electronixandmore.com/adam/images/6b4g_amp/copy_currentschem.jpg SRPP 6SN7 I'm open to SS rectification. My DIY Zen SE84 uses it and it sounds fine. I understand the benefits. A tube rectifier IS classic though and would add more resale value I think. = ) Maybe just build it with a tube rectifier and experiment with SS at some point.
@@jdsalinger73 I had never heard of the DC Loftin-White amplifier so I looked it up. I learn something from you guys that watch my videos all the time. There is a charm about the old triodes that many of us like. I tend to stick with PP amplifiers as I want a little more power than a SE amplifier can deliver. I have built too many amplifiers myself and posted one just a few hours ago. The amp I posted is not for me and is much too large for my taste. Anyway, it sure sounds like you have a plan. Best of luck with it and it would be nice if you posted it on RUclips for all to see.
@@jdsalinger73 One more comment. I looked at your links and the designs are really interesting and I don't quite understand them. I think I would model them with LTSpice before building them. If you don't have LTSpice you get it free from the link below. If you haven't used it before it is a challenge to get up and running but it is worth it in my opinion. www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html
the 4CX500A (uses a strange socket) is a good vacuum tube but needs forced air cooling. could you not use a wide band notch filter to remove the undesirables and clean he signal up a bit, what about building a HIFI amp around 2x 4CX500A as the output stage but you will need forced air cooling and you will have to have it installed somewhere where the noise of the cooling fan is not objectionable.
I found a design in the RCA Receiving Tube Manual for 45 watt PP 6L6 AB2 amplifier. But it uses an Input Transformer between the driver stage and the 6L6's. Having trouble finding one so I'm thinking are these really used anymore ? Would capacitor input work just as well to the finals ? What are your thoughts on the benefits of using an Input Transformer for Inter-stage coupling ? Thanks for your great videos !
There are some that seem to have an undying love for interstage transformer coupling but I don't use them. As you say, hard to find, probably expensive and who knows what the results are going to be. Here is a video I made some time back on transformer vs capacitor coupling. Thanks for your comments.
I guess the little sound card became somewhat of a permanent thing... that's pretty useful. I'd like to hear your opinion on regulated power supplies for tube amplifiers. I guess I am a little obsessed with hum and have been flirting with the idea of a big regulated B+ power supply, like in the old Tek scopes, actually using the old 6080's and power transformers I salvaged over the years. I guess the same would go for DC regulated filaments... Do you think it's worth? I'd really like to hear your thoughts on that. Thanks for another pretty cool video.
My experience is that the big Tek scope transformers are more than a little problematical re-purposed for audio amps. We'll forget about them weighing so much. Usually there is only one winding with sufficient ampacity for a pair of fat output tubes; let's say 125+ mils. But that winding can only produce about 300 volts. So you start thinking, let's put a couple of windings in series. You can produce almost any voltage by combining windings you wish (and there are plenty of them) but NONE of the other HV windings are rated for that much current. And some of them are rated for almost nothing, like 10-20 mils, so you risk flaming something if, as part of a series circuit, you run 100+ mils through them; at least on paper, maybe you can get away with it. Then we get into discussion of the 6080's. As nice and impressive as they look, they are very inefficient tubes, I believe they use 2.5 amps heater current, and of course you have all that (and 6-8 other 6.3 volt windings) on your scope transformer, but the scope transformer makes it hard to get your 450 volts that you want for 6L6s or 6550s. So, if you now get another power tranny, then you won't have enough 6.3 current to run 6080's. Argggggh. Now you want to reduce hum by using a regulated B+ supply and/or heaters. Every experiment I have seen has shown that the benefits are quite minor. On the output tubes, hum is reduced/canceled primarily by the push-pull action of the output tubes. A reg B+ supply *may* help the preamp section which would probably give you some hum reduction and it is THERE where I would focus. But even there....preamp tubes use 1-2-3 mils and do not change much so why you would need a ragulated supply is...questionable. Should you decide to do so, though, that would be a blessing because you'd be dealing with only 250-300 volts gross B+ and only a few mils current. I've seen plenty of experiments where folks went to great effort to run DC heaters and reported only the most tiny (or zero) improvement over standard good lead dress. IMO you get better action with a hum balance pot or even a synthetic center tap on the 6.3 volts. I am not trying to tell you I have conducted extensive tests with top grade lab gear on these issues, I am just passing on the results that at least a dozen other builders have reported. My more important bottom line: Scope trannies are not good for amps. At all. The big issue here is that you carve up a chassis for one of those monsters understandably thinking you'll have all the power you need because of the physical size....and then you run into the current/voltage issues and find they are not a good choice. That much *IS* my direct experience.
pneumatic00 You are right as they do have a lot of low current windings on the ac section of their secondaries. I just think it’s such a waste to see these transformers sitting around ....maybe I’ll rewind their secondaries into something a little more useful, it’ll be a little more work but I ain’t afraid of winding and sealing transformers, actually, I’ve had some pretty good luck with output transformers in the past, I guess I would only need to build another winding jig. When it comes to filament, hum, well...I’ve been having some luck just using an artificial center tap with a pair of 100ohm resistors. I did play with balance pots but never saw much improvement over the artificial center tap. Thanks for sharing your experiences.
As long as you are in class A you have practically a constant current draw, so need for silicon rectifiers. Yes, the B+ will be higher, but you could also use a higher AC secondary so that is no argument.
Valve rectifiers are useless, unless already fitted in a guitar amp. Why waste 15w? Valves are bad enough as it is, from an efficiency POV that is, wasting more watts on rectification is just plain daft. Interesting that the third harmonic was higher than the 2nd, not enough to worry about though. 6SN7's are far better than ECC82's/12AU7, distortion wise that is. Morgan Jones tested all the SN7 family as well as 12AU7's etc. 6SN7's came out top. See Morgan Jones - Valve Amplifiers. Interesting video as always. BTW, would appreciate a video on pi filters, how to calculate C1, C2 and anything you know about swinging chokes. Also how to measure inductance with DC present.
Guitarist use a distorted sound for rock and prefer the over driven valve sound. Some hi fi buffs like tube amps for their open sound despite the higher distortion and yet they stride for perfection in audio reproduction . Strange how are brain behaves.
![Seungmin "그렇게, 천천히, 우리(As we are)" | [Stray Kids : SKZ-PLAYER]](http://i.ytimg.com/vi/kAzmhLHePqU/mqdefault.jpg)
Genius again. I started sending people to your channel rather than continuing to try and get them to provide accurate information instead of folklore to their subscribers.
You make a clear, simple and non-mathematical case for why actual knowledge and experience are important. RUclips is stuffed full of people whose only sorce of information is RUclips itself. It is a viscious, circular race to the bottom.
I watched a whole series wherein a guy utterly destroyed an irreplacable, priceless old receiver by putting bigger, better looking caps in and correcting the manufacturing defects where Pioneer had left out key parts. Of course, the PCB was used for several products. Nothing was left out. Now, the old machine has several corrected circuits and better caps - but next time, he will use even bigger caps because he still doesn't think it's right.
GROAN!
There is no way to fix the RUclips problem. All we can do is point people in the right direction. I am so glad people like you take the time to produce real content.
I am sorry about the spelling. I am writing on a phone while riding a train. You can understand what I mean.
Thank you for the insights and tour of your workspace. I service Fender, Hiwatt, Marshall, and various tube guitar amps for myself and other local musicians in my area. Your videos are very informative and help me apply what I learned years ago and did not fully use until this later stage in my journey. Two thumbs up!
I love the 6B4G. You did a very nice job as usual David.
The removable wall outlet sockets are called IEC sockets! there are also versions with fuses and mains voltage selectors on the same socket
Nice vid, and thanks for the tour of your lab.
Sir, You are a mighty man. . I enjoy all your videos. Keep it up.
The purpose of the grid stopper resistor is to improve the stability of the amplifier by reducing the possibility of high frequency self oscillation. This works because of the resistance of the grid stopper reacting with the capacities on the grid of the vacuum tube forming an RC lowpass filter network.
Just watching these videos from El Paso I lean a bunch , even if I don't plan on building a tube amp or whatever the video may be about.
Those "spurs" look like IM Distortion. Specifically, the 60Hz & 120Hz power supply noises modulated onto the fundamental as well as each of it's upper harmonics. Using a regulated DC voltage or current supply for the filament may greatly reduce this effect (since these are direct heated triodes).
Gary Trautman Another way to look at it would be as AM sidebands. The heater AC is amplitude-modulating the 1KHz sine wave carrier. When you balance the heater AC properly in a PP output stage it cancels out inside the output transformer,as does the hum.
Dc supplies significantly lower the life of the filament due to cathode posioning ac supply is fine if it's done right. just cause u can measure it don't mean u can hear it if u can't hear it it don't exsist. Maybe u could do DC on preamp tubes like some new production tubes u don't care about or u could just use tubes made to minimize hum 6eu7 shielded 6cg7 with cross talk speperator comes to mind perhaps some tube shields. But I would never never ever put DC on expensive output tubes cause actually it's useless power tube have some much ps rejection since they sink current and not voltage and not to mention it shortens there life. so there is my two cents
Dave,
What grid "stoppers" stop is parasitic oscillation. The higher the gm of the tube, the more vulnerable to parasitic oscillation it is. It is a rule of thumb among DIYers to assume parasitic oscillation will be present and install the stoppers, from the very beginning. As gm goes up, so should the stopper value. For instance, I call for 100 Ω on 12AX7 grids and 1.5 Kohms on 6922 grids. I strongly prefer carbon comp. parts as "stoppers", given they are both non-metallic and non-inductive.
Speaking of carbon comp. parts, when dealing with "ancient" NOS, bake them in the kitchen oven, to drive off absorbed atmospheric moisture, before taking measurements.
You will see in some schematics very large valued "stoppers" on the O/P tube grids. Those parts are doing double duty. Aside from parasitic oscillation, they also help in "taming" blocking distortion.
Eli D.
Hi Eli,
I know your comment is a year old and for reasons I don't always understand, I don't see comments in a timely manner when you guys reply.
Anyway, I really appreciate your advice and I do nowadays use grid stoppers. I think I have learned from you guys and you did a great job of explaining it and the reasons for using "stoppers". I have even recently taken that a bit further and use stoppers or maybe call them isolation resistors, in the screens and even the plates of parallel push-pull amplifiers like a quad 1625 modulator I recently built. By installing 47 ohm resistors in the plate leads and 100 ohm resistors on each screen (if my memory serves me at the moment) it completely stabilized and otherwise very unstable amplifier. Just did magic for it. Thanks again. Stay safe.
I'm desperately looking for resource to find out what some of my vacuum tubed equipment is , one looks like a time machine and and old tubed IBM computer something or another and I just might be curious enough to plug this in one day , so for possibly the sake of humanity, please help me find a resource
Great video. Very helpful. I've built a number of tube guitar amps now and am really enjoying them. I'm interested in trying a hifi amp. I currently have a pair of Overnight Sensation desktop speakers with 25 watt drivers that I use with an old solid state receiver. I'd like to built a tube hifi amp to replace that receiver. I'd just be listening to music in my study. Not terribly loud. Any suggestions on circuits I could look at for inspiration?
For some really good ideas take a look at these files. There are four parts,
www.google.com/search?q=100+amplifiers+part+2&rlz=1C1CHBF_enUS757US757&oq=100+amplifiers&aqs=chrome.3.69i57j0l5.7555j0j8&sourceid=chrome&ie=UTF-8
You can find them all by Googling, "100 Amplifiers - Part 3", etc
.
I personally would use a 6L6 as an output tube (also known as a KT66) and a Williamson design.
The Heathkit W5M is a good one and there is a little bit older design with 6SN7's that is my favorite
.
www.mcmlv.org/Archive/HiFi/HeathkitW5M.pdf
I like vintage Acrosound transformers or new James Audio transformers for the output.
www.tubebooks.org/file_downloads/acrosound.pdf
These amplifiers are in the 20 watt range which is plenty for efficient speakers.
Extremely helpful, thank you!
Hi, Id like to know if its important to have the right filament voltage ,cause i made an single end kt66 and the power transformer give me 7 v unladen and 6.8 v loaded ,i see on the forum the guys says life tube is longer with 6.3 v exactly ,so regulation on filaments may be a solution ,what do you think about!
Usually, filament voltages do measure 7 volts or more at the transformer terminals when unloaded. That is normal. It is better to have filament voltage a bit high than low. I had some foreign made 300B that when run at 5.0 volts on the filaments, would not perform. I had to raise the filament voltage to around 6 volts to get the tubes to perform correctly. Obviously, a QC problem with the tubes. People worry way too much about how long their tubes are going to last. I had rather run my tubes with a higher filament voltage and have good performance than have them run poorly or marginally at some text book level or what some forum says. Your 6.8V is perfectly OK at the filament pins, and then move on to the rest of the design and build of the amplifier.
Thank you for your advice .have a nice day@@ElPasoTubeAmps
Grid stopper Resistors along with the capacitance of the Tube form a low pass filter, Thus providing frequency compensation, In addition this Resistor provides a Real Impedance for situations where the Grid turns Inductive and can result in a negative Impedance. Grid stopper resistors are also used with Transistors, however are called Base stopper Resistors.
Thanks, Philip. It took me quite a while to be convinced that they had a real value but I am convinced now. The most dramatic situation I had was a McIntosh amplifier build that I have shown a number of times on YT where when the input gain pot was almost all the way down (lease amount of input) the amplifier would often times go into a parasitic. It puzzled me as I knew it was a good design but the issue was finally explained to me much like you just described it. I am a believer now. Thanks for your comment.
Thanks for sharing your years of knowledge! Subscribed.
Another good video. You CAN teach an old dog new tricks. Greatly Appreciated.
I've heard from several that a tube rectifier is easier on the other tubes since the B+ doesn't appear right away.
With the direct heated rectifier tubes like the 5U4 and 5Y3, the DC comes on strong in just a few seconds. 5AR4 and 5V4 take a little longer to heat up so maybe they are all a little less stressful on the electrolytic's in the PS as it gives a few more seconds for the other tubes to warm up and load the PS.
Just found you. Great stuff. I'm into amps, radios and BW TVs.
I've read that you should draw at least 1/10th of the maximum current a transformer is designed for, to have a stable voltage output
Once again a great and informative video well done 👍
The voltage measurement on startup and capacitors ratings getting over could be some nice new video if you didn't do it already (?) last but not least I believe you Feed that focusrite soundcard on the mic input, so unless there's a mic/line switch available on the software that's why you need to attenuate the input like that.
The next video is already in my head. I know the LTSpice videos are not the most popular but to see the way different values for chokes and capacitors perform in a Pi network in a power supply might be a real "eye opener".
As for the Focusrite, I do keep it in the line position (it has a switch) and it will take 5 VRMS input with the gain on the sound card at the 12 o'clock position and remain green so it's not too hard to keep the drive down.
Question? What device uses two OD3a tubes with a large transformer and a huge cap ? Is it a power supply ? I bought this thing off an estate sale and for 20 bucks and it seems to work. From what I understand, the OD3a tubes are pretty expensive. If so, what is this for ?
I am having a hard time finding information about the tube equipment my grandpa's friend gave me , although I have a
I have that same triplette meter in the background. The ohm scale dosen't work anymore and I'm guessing its a battery. Do you know what kind of batteries they use?
BurningTirez It is usually a 1.5V D cell. Many people remove it and put in a 1.5VDC supply powered by the heater AC. You can do it with a capacitor and three diodes, one to1/2-wave rectify and two in series as a shunt regulator. I am about to do it with a diode, a capacitor, an LM317, and two programming resistors, which will waste a lot less heater current. You don't want to be fiddling around with batteries in this day and age, even though in a VTVM they will last a decade or so.
BTW, I've found that the film capacitor used for DC Link Bus and IGBT Snubber applications are far superior for noise rejection. It's actually hard to determine which terminal is connected to the outer foil.
Hi Gary, I actually don't know what you are talking about, I just understood the last sentence.I was going to say that Mr Carlson's Lab has a video on figuring out which lead is the outer foil. I just marked out about 40 caps last night using the oscilloscope. As I don't use enough caps for the hobby, I didn't build the unit he build's in the video (don't know if I could), just used the scope as he shows.
Sounds like you do know ;-) Finding the outside foil of the typical cylindrically wound film capacitor is very easy - the outside foil can't reject noise. The various DC Link & IGBT Snubber Caps that I have tested are not nearly as sensitive - Carlson's method will fail to identify the outer foil reliably. Not sure how these caps are constructed, but something is definitely different. They are also epoxy encapsulated & very well constructed, eliminating the microphonics most film caps suffer from.
David, are we going to see an attempted repair of the Mcintosh Receiver? I for one would enjoy it. I enjoyed this video as well. Always like to hear your opinions on things... Take care, Tom
Hi Tom,
Well, now that you have mentioned it, I guess I have no excuse not to try. I hadn't seriously thought about it but I do have a schematic of it and the test equipment. I just really don't like working on SS equipment. This would be like going back to work...
I would have to work quickly as in about 10 minutes it settles down and works fine. This particular receiver/preamp has a lot of noise in the tuning process. It always has had that issue and in the past I have run the tuning dial from one end to the other a couple of times and it quietens down as it is tuned up and down the band but I don't remember the volume going up and down in the past just sitting on one station. I have had this unit 20 years or more. It is old style tuning with a variable capacitor. I suppose it could help others with this issue if I can find a real fix for it. I will give it serious consideration. Thanks for your comment.
I put the MX112 on the bench and took the covers off, etc. ready to figure it out and it worked great. No issues. I guess it was just bad connections/cables between the tuner and the amp. I did change out the cables.
That's good news. It would have been interesting to see you diagnose/repair a problem on the receiver if there was one, but I'm glad for you that there isn't.
An electric guitar amp is an instrument itself. That's why some prefer a tube rectifier or a silicon diode rectifier, depending on musical style and role in the mix.
Maybe some time you could tell us about some of your antenna builds?
Thanks! Very informative.
I have made a few 2.4 GHz antenna videos and one video for log periodic antennas that I made and use for TV and FM stereo reception. The only antenna I have up right now for HF is an aluminum tubing rotating dipole for 20M. Years a go I was into yagi antennas (VHF and HF) with gamma capacitor feed and that was a lot of fun but nowadays I just operate 20M. I am very much a believer in the use of the so called, "choke balun" as it works great for me. Simple to make and cheap. However, these chokes must be built for each band as a single one will not work for the whole HF band.
How are you measuring AUDIO power output in WATTs with the Tektronix DMM 4020?
It has that feature. You do a shift and set REF(ohms), in my case usually 8 ohms, and then go to AC and it allows power, dB, etc.
I'm preparing to build a 6B4 stereo amp. You've given me a lot to think about.
SS rectification vs. tube.
Was planning on parallel 12AX7 drivers, now I'm not sure. I've heard that 2A3/6B4 types need a high mu tube and I've seen both 6SN7 & 6SL7. So confused!
Ground buss wire or star ground?
I will try to tell you what I think about it.
First off, we do not need power to drive the 6B4G triode. We need voltage. They run class-A so they need no grid current. Typical RC coupled stages deliver around 50 volts drive and the 6B4G runs around -45 bias at 250 volts on the plate. So RC coupling should be OK. I assume you will get your bias by way of cathode resistor and bypass capacitor.
What this leads up to is if one wants more voltage drive for the grids of the output tubes, it can be solved with a choke, sometimes known as impedance drive. The chokes are available and are expensive and are around 2500 H.
Study this schematic and see that Altec drives push pull 813 to 260 watts with a 6AU6 and the impedance choke
www.vintagewindings.com/gen%20pop/8299543VW8335/Altec/Altec-260A.pdf
The 6SL7 is a high mu triode just like the 12AX7 and the 6SN7 is a medium mu triode just like the 12AU7. Assuming you want around 1.5 volts input to drive your amplifier to full output, you only need a medium mu triode. I generally avoid the 6SL7 as it has so much gain only 100 mV or so will drive the amplifier to full output and it is very easy to overload the input to the amplifier.
Acrosound published some beautiful schematics back in their day. I recommend using their design. As some on the Internet do, "let's try this and let's try that and see what happens" usually leads to a poorly performing amplifier.
SS or vacuum tube rectifiers are just a choice. The rectifier tube is pretty so people still use them.
Here is the Acrsound catalog with schematics.
www.tubebooks.org/file_downloads/acrosound.pdf
In my opinion, one of the best simple Williamson amplifiers ever built is the Heathkit.
Here is one version with 12AU7's and KT66's (you can use your 6B4G's in place of the KT66's). I assume you know 6B4G's have a directly heated cathode and require a pot of 5 watts or better around 25 to 100 ohms for a cathode return to ground and hum adjustment as the indirectly more modern tubes do not.
www.ampslab.com/vintage_heathkit_w5m.htm
Here is the Heathkit with 6SN7's (my favorite)
www.nostalgickitscentral.com/heath/schematics/heathkit_schema_w4am.pdf
Lastly, here are some more schematics (there are five books like this. Just change the part-3 to part 1 thru 5
lilienthalengineering.com/100-amplifiers-chapter-1/100-amplifiers-part-3
I almost forgot the grounding - ground all of your power supply components (CT of transformer, electrolytic capacitors, etc to a single point on the chassis). I have found the complicated star and buss grounds unnecessary and messy. You can ground cathodes and inputs right to the chassis. Study the grounding scheme of a McIntosh amplifier and you will see how the real pros do it.
Hope this helps.
Thanks for the quick response! If I knew you'd write such an informative response I would have been more accurate. I'm actually planning a DC Loftin-White inspired 6B4G. Originally I was thinking SE EL43 or 6L6 but I've already built one (super great amp...just so many yet to build and experience). Never heard a SE DHT though, and I've heard...there ought to be a law that EVERYONE has to experience a DHT at some point. Already have a pair of Russian 6B4's on the way.
I think I've narrowed it down to a couple circuits. www3.sympatico.ca/wenchieh/2A3_schematics/shishido.jpg 12AX7 in parallel
www.electronixandmore.com/adam/images/6b4g_amp/copy_currentschem.jpg SRPP 6SN7
I'm open to SS rectification. My DIY Zen SE84 uses it and it sounds fine. I understand the benefits. A tube rectifier IS classic though and would add more resale value I think. = )
Maybe just build it with a tube rectifier and experiment with SS at some point.
@@jdsalinger73 I had never heard of the DC Loftin-White amplifier so I looked it up. I learn something from you guys that watch my videos all the time.
There is a charm about the old triodes that many of us like. I tend to stick with PP amplifiers as I want a little more power than a SE amplifier can deliver.
I have built too many amplifiers myself and posted one just a few hours ago. The amp I posted is not for me and is much too large for my taste.
Anyway, it sure sounds like you have a plan. Best of luck with it and it would be nice if you posted it on RUclips for all to see.
@@jdsalinger73 One more comment. I looked at your links and the designs are really interesting and I don't quite understand them.
I think I would model them with LTSpice before building them. If you don't have LTSpice you get it free from the link below. If you haven't used it before it is a challenge to get up and running but it is worth it in my opinion.
www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html
the 4CX500A (uses a strange socket) is a good vacuum tube but needs forced air cooling. could you not use a wide band notch filter to remove the undesirables and clean he signal up a bit, what about building a HIFI amp around 2x 4CX500A as the output stage but you will need forced air cooling and you will have to have it installed somewhere where the noise of the cooling fan is not objectionable.
I found a design in the RCA Receiving Tube Manual for 45 watt PP 6L6 AB2 amplifier. But it uses an Input Transformer between the driver stage and the 6L6's. Having trouble finding one so I'm thinking are these really used anymore ? Would capacitor input work just as well to the finals ? What are your thoughts on the benefits of using an Input Transformer for Inter-stage coupling ?
Thanks for your great videos !
There are some that seem to have an undying love for interstage transformer coupling but I don't use them. As you say, hard to find, probably expensive and who knows what the results are going to be.
Here is a video I made some time back on transformer vs capacitor coupling.
Thanks for your comments.
Thank you for the information. I enjoyed it.
Do you like a RHOMBIC Antenna?
I guess the little sound card became somewhat of a permanent thing... that's pretty useful. I'd like to hear your opinion on regulated power supplies for tube amplifiers. I guess I am a little obsessed with hum and have been flirting with the idea of a big regulated B+ power supply, like in the old Tek scopes, actually using the old 6080's and power transformers I salvaged over the years. I guess the same would go for DC regulated filaments... Do you think it's worth? I'd really like to hear your thoughts on that. Thanks for another pretty cool video.
My experience is that the big Tek scope transformers are more than a little problematical re-purposed for audio amps. We'll forget about them weighing so much. Usually there is only one winding with sufficient ampacity for a pair of fat output tubes; let's say 125+ mils. But that winding can only produce about 300 volts. So you start thinking, let's put a couple of windings in series. You can produce almost any voltage by combining windings you wish (and there are plenty of them) but NONE of the other HV windings are rated for that much current. And some of them are rated for almost nothing, like 10-20 mils, so you risk flaming something if, as part of a series circuit, you run 100+ mils through them; at least on paper, maybe you can get away with it. Then we get into discussion of the 6080's. As nice and impressive as they look, they are very inefficient tubes, I believe they use 2.5 amps heater current, and of course you have all that (and 6-8 other 6.3 volt windings) on your scope transformer, but the scope transformer makes it hard to get your 450 volts that you want for 6L6s or 6550s. So, if you now get another power tranny, then you won't have enough 6.3 current to run 6080's. Argggggh.
Now you want to reduce hum by using a regulated B+ supply and/or heaters. Every experiment I have seen has shown that the benefits are quite minor. On the output tubes, hum is reduced/canceled primarily by the push-pull action of the output tubes. A reg B+ supply *may* help the preamp section which would probably give you some hum reduction and it is THERE where I would focus. But even there....preamp tubes use 1-2-3 mils and do not change much so why you would need a ragulated supply is...questionable. Should you decide to do so, though, that would be a blessing because you'd be dealing with only 250-300 volts gross B+ and only a few mils current. I've seen plenty of experiments where folks went to great effort to run DC heaters and reported only the most tiny (or zero) improvement over standard good lead dress. IMO you get better action with a hum balance pot or even a synthetic center tap on the 6.3 volts. I am not trying to tell you I have conducted extensive tests with top grade lab gear on these issues, I am just passing on the results that at least a dozen other builders have reported.
My more important bottom line: Scope trannies are not good for amps. At all. The big issue here is that you carve up a chassis for one of those monsters understandably thinking you'll have all the power you need because of the physical size....and then you run into the current/voltage issues and find they are not a good choice. That much *IS* my direct experience.
pneumatic00 You are right as they do have a lot of low current windings on the ac section of their secondaries. I just think it’s such a waste to see these transformers sitting around ....maybe I’ll rewind their secondaries into something a little more useful, it’ll be a little more work but I ain’t afraid of winding and sealing transformers, actually, I’ve had some pretty good luck with output transformers in the past, I guess I would only need to build another winding jig. When it comes to filament, hum, well...I’ve been having some luck just using an artificial center tap with a pair of 100ohm resistors. I did play with balance pots but never saw much improvement over the artificial center tap. Thanks for sharing your experiences.
As long as you are in class A you have practically a constant current draw, so need for silicon rectifiers. Yes, the B+ will be higher, but you could also use a higher AC secondary so that is no argument.
Valve rectifiers are useless, unless already fitted in a guitar amp. Why waste 15w? Valves are bad enough as it is, from an efficiency POV that is, wasting more watts on rectification is just plain daft.
Interesting that the third harmonic was higher than the 2nd, not enough to worry about though.
6SN7's are far better than ECC82's/12AU7, distortion wise that is. Morgan Jones tested all the SN7 family as well as 12AU7's etc. 6SN7's came out top. See Morgan Jones - Valve Amplifiers.
Interesting video as always. BTW, would appreciate a video on pi filters, how to calculate C1, C2 and anything you know about swinging chokes. Also how to measure inductance with DC present.
Guitarist use a distorted sound for rock and prefer the over driven valve sound. Some hi fi buffs like tube amps for their open sound despite the higher distortion and yet they stride for perfection in audio reproduction . Strange how are brain behaves.