What should I build with a 8K 10W PP transformer with available 40% UL taps?
the simpler the better.
the simpler the better.
PP 2a3. Heat them up simply with a couple of Hammond 266M5 transformers. If you want cheap, then 6C4C which is the Russian 6B4G, but you'll need a humbucking circuit or DC filaments with voltage regs - more complex.
For the input section how about an EC86 aka 6CM4, or the Russian equivalent 6S4P-EV? Enough gain for 2 stages - could be a diff pair or concertina front end.
For the input section how about an EC86 aka 6CM4, or the Russian equivalent 6S4P-EV? Enough gain for 2 stages - could be a diff pair or concertina front end.
Thank you for the reply. A PP 2A3 is quite tempting. I sometimes forget how little I really know about tube amps and then I read posts from people that really understand the design of them. I can usually follow a proven schematic but for figuring out designs and twerking them I get in over my head fast.
Hi invaderzim,
You did not provide the context needed to give you a useful reply. What speakers do you want to drive? What is the budget? What is the quality of your output transformers? If you want to go simple and inexpensive, and still be able to drive speakers of average efficiency I would suggest one of the many 6V6 tried and true designs using 10k UL transformers, or EL84. Unless you have really good transformers, I would think your expenditure on 4x2A3 output tubes (a minimum of $200 per quad) will not be justified. Additionally, your 10k output transformers are about twice the recommended impedance for a PP pair of self-biased 2A3 tubes, and tree times what is needed for fixed bias. (Granted you could hook up your 8 ohm speakers to your 16 ohm taps and get closer to ideal primary impedance).
You did not provide the context needed to give you a useful reply. What speakers do you want to drive? What is the budget? What is the quality of your output transformers? If you want to go simple and inexpensive, and still be able to drive speakers of average efficiency I would suggest one of the many 6V6 tried and true designs using 10k UL transformers, or EL84. Unless you have really good transformers, I would think your expenditure on 4x2A3 output tubes (a minimum of $200 per quad) will not be justified. Additionally, your 10k output transformers are about twice the recommended impedance for a PP pair of self-biased 2A3 tubes, and tree times what is needed for fixed bias. (Granted you could hook up your 8 ohm speakers to your 16 ohm taps and get closer to ideal primary impedance).
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Forgot to mention - if your budget is tight you might want to look at the Russian 6P1P output tubes which can still be bought for little money. The 6P1P-ev (military version) will sound good with your 10k UL output transformers and deliver the rated 10 watts. (For PP 2A3s you really need >15watt transformers.)
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Transformers are 8K and they would work great with 2A3s: 8W pure class A and very low distortion with the tubes running at 300V/50mA.
The 6C4C is very good and actually from the mechanical construction point of view is actually better than most US vintage 2A3's....
Only trouble is that filaments need DC supply at least. They can be found for $ 25-30 each easy. With more patience and luck maybe less.
Other tubes like the EL84s would make the build easier for sure and are a very safe bet performance wise too.
The 6C4C is very good and actually from the mechanical construction point of view is actually better than most US vintage 2A3's....
Only trouble is that filaments need DC supply at least. They can be found for $ 25-30 each easy. With more patience and luck maybe less.
Other tubes like the EL84s would make the build easier for sure and are a very safe bet performance wise too.
Yea, 2a3 tubes are a bit expensive but the sound is worth it. The OP didn't say what OPTs. However, I wouldn't worry about a higher primary impedance. I like my 300bs with a 5K OPT in self bias and others do too. It's a valid choice. Like I said, the 6C4C is a cheap alternate. I'm a fan of directly heated tubes wherever possible.
It sounds like you already have the 8k p-p UL transformers.
If you do not need much power . . . check out my amplifier thread on Tubes / Valves:
Search for the thread from 14 July 2019:
Thread title: "A Simple Low Power 7591 Push Pull Amplifier"
I built one Mono-Block amp.
The indirect heated filaments make it easy to wire.
I used a 10k plate to plate (p-p) UL transformer, but 8k and 40% taps will work very well too.
I only had one 10k p-p UL transformer, but I have two 8k p-p UL transformers, so I will build two mono-blocks using the 8k pair.
If you need more damping, and can work with a little less power than Ultra Linear, then Triode wire the 7591 tubes (Triode wired: 100 Ohms from Screen to the Plate; versus Ultra Linear: 100 Ohms from Screen to the UL tap).
If you need more power than my simple 7591 push pull amp . . .
Then build a totally different amplifier.
We still did not hear:
What speakers will you use?
Efficiency?
What room size?
How loud you like to listen?
Etc.
That is part of determining what power you might need.
If you do not need much power . . . check out my amplifier thread on Tubes / Valves:
Search for the thread from 14 July 2019:
Thread title: "A Simple Low Power 7591 Push Pull Amplifier"
I built one Mono-Block amp.
The indirect heated filaments make it easy to wire.
I used a 10k plate to plate (p-p) UL transformer, but 8k and 40% taps will work very well too.
I only had one 10k p-p UL transformer, but I have two 8k p-p UL transformers, so I will build two mono-blocks using the 8k pair.
If you need more damping, and can work with a little less power than Ultra Linear, then Triode wire the 7591 tubes (Triode wired: 100 Ohms from Screen to the Plate; versus Ultra Linear: 100 Ohms from Screen to the UL tap).
If you need more power than my simple 7591 push pull amp . . .
Then build a totally different amplifier.
We still did not hear:
What speakers will you use?
Efficiency?
What room size?
How loud you like to listen?
Etc.
That is part of determining what power you might need.
The transformers are going to limit the power you can *get*, regardless of tubes. 10 watts at low frequency. If you push the power much higher, your low end will suffer. Might be ok for 20 to 40 watts above 100 Hz, for music (not sine waves). I wouldn’t try to go higher than 2 or 4X the power rating, even if you high pass it and use a sub for bass.
10 to 20 watts is certainly do-able with push pull triodes or triode strapped pentodes without getting into insane voltages, even at 8k load.
10 to 20 watts is certainly do-able with push pull triodes or triode strapped pentodes without getting into insane voltages, even at 8k load.
Sorry for leaving out important details and thank you for all the replies.
It would be a small room with speakers only a few feet away at fairly low listening levels. The current speakers are small and about 85dB I ran a DIY Push-Pull (PP) 6V6 / 6V6GT Tube Amplifier Schematic on those speakers before and it had plenty of power but never really wowed me, but without a scope I was just guessing at dialing in the global feedback. The transformers are cheap antek ones. If I could collect up the rest of the parts for around $500 it would be nice.
It would be a small room with speakers only a few feet away at fairly low listening levels. The current speakers are small and about 85dB I ran a DIY Push-Pull (PP) 6V6 / 6V6GT Tube Amplifier Schematic on those speakers before and it had plenty of power but never really wowed me, but without a scope I was just guessing at dialing in the global feedback. The transformers are cheap antek ones. If I could collect up the rest of the parts for around $500 it would be nice.
Why do we have to try and get someone to build a more expensive, higher power,
more high end amplifier?
If he only needs 5 Watts or so and balances the quiescent push and pull DC currents, there is not a problem. Bass will be clean.
But perhaps he has low efficiency speakers, and wants to listen to pedal C of a pipe organ,
about 30Hz.
And what speakers do that real well?
might need new speakers too.
I do not think he asked for a 40 Watt amplifier.
He asked for simple, and to use the transformers that he has in hand.
He asked what could he build using those transformers.
Get back to what was asked in the original post.
If we keep making it more costly, more complex, and too many more options, he may never build an amplifier.
Is that what this forum is all about?
Sorry, but I had to say all that.
I took time to write this post, so I did not see the original posters response in Post # 10.
So, now, all of you out there have a challenge. Either come up with a modification of the amplifier that he has that will cause it to wow him; or with a new design that will use his new output transformers, and that will wow him; or move him over to the loudspeakers threads.
more high end amplifier?
If he only needs 5 Watts or so and balances the quiescent push and pull DC currents, there is not a problem. Bass will be clean.
But perhaps he has low efficiency speakers, and wants to listen to pedal C of a pipe organ,
about 30Hz.
And what speakers do that real well?
might need new speakers too.
I do not think he asked for a 40 Watt amplifier.
He asked for simple, and to use the transformers that he has in hand.
He asked what could he build using those transformers.
Get back to what was asked in the original post.
If we keep making it more costly, more complex, and too many more options, he may never build an amplifier.
Is that what this forum is all about?
Sorry, but I had to say all that.
I took time to write this post, so I did not see the original posters response in Post # 10.
So, now, all of you out there have a challenge. Either come up with a modification of the amplifier that he has that will cause it to wow him; or with a new design that will use his new output transformers, and that will wow him; or move him over to the loudspeakers threads.
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Really, it's relatively easy to make a good sounding 5W PP triode amp.
6A3sUMMER's simple design is similar to a couple of other well-liked amps like Poindexter's Musical Machine and Eli Duttman's El Cheapo (and El Cheapo Grande).
Can you see the family resemblence? 😉
The same basic circuit with 8k OPTs can use PP EL34-triode, 6L6GC-triode, 7591A-triode, 6P1P-triode, 6V6GT-triode, or EL84-triode.
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With “cheap” output transformers I might be inclined to use cheap output tubes, and certainly not try to get more than the 10 watts out of it. Maybe use 6W6’s in triode instead of 6V6? And get a little closer to 10 watts out of them. Needs more heater power, but lower Rp. Bump them up into class A (at a little lower B+) and you may or may not even want global NFB.
If a 6V6 PP amp doesn't wow the OP, then it has to be a step up from that in sound quality. OPTs can be upgraded, so it's worth using a better set of tubes. The 7591 has good gain and could be driven with some DHTs like 2P29L or 26. That's a more demanding build, though. Frankly, I think the simplest solution is a basic 2 stage SE 300b amp - start again and plan it properly.
But otherwise, a PP EL84 amp in triode (more gain than 6V6) has potential. The upgrade in sound quality would have to come from the input section. I'm wondering about this one....
Push-pull EL84 amplifier | Firebottles!
Push-pull EL84 amplifier | Firebottles!
But otherwise, a PP EL84 amp in triode (more gain than 6V6) has potential. The upgrade in sound quality would have to come from the input section. I'm wondering about this one....
Push-pull EL84 amplifier | Firebottles!
Push-pull EL84 amplifier | Firebottles!
The 6V6 family makes a better triode than the 6BQ5/EL84. Comments have been made that, for this power range, you need to use #45 DHTs to get better sound.
The 10 W. iron will saturate, if placed inside a GNFB loop and a multi-grid mode is employed.
Roughly 6 WPC will be realized from PP triode wired 6V6s that rarely enter the Class "AB" environment. Poindexter's "Musical Machine" will squeeze everything possible from those 10 W. trafos the OP already possesses. Poinz went through several design iterations. AFAIK, the most recent iteration uses 2X 6GK5s and a tail CCS in the LTP.
As is always the case, the "iron" makes the amp.
The 10 W. iron will saturate, if placed inside a GNFB loop and a multi-grid mode is employed.
Roughly 6 WPC will be realized from PP triode wired 6V6s that rarely enter the Class "AB" environment. Poindexter's "Musical Machine" will squeeze everything possible from those 10 W. trafos the OP already possesses. Poinz went through several design iterations. AFAIK, the most recent iteration uses 2X 6GK5s and a tail CCS in the LTP.
As is always the case, the "iron" makes the amp.
The schematic for the '06 Machine looks pretty promising. I have a power transformer already that will get me right around 300v. I'll have to find a power supply schematic that matches up with that version.
I'm not apposed to upgrading the output transformers at some point, when/if transformers become more readily available again.
I'm not apposed to upgrading the output transformers at some point, when/if transformers become more readily available again.
This might be a candidate - the original Baby Huey, using affordable PCL86 instead of ECL86.
Dissident Audio PP_ECL86
Dissident Audio PP_ECL86
I have never found a tetrode that makes a good triode.
It's not 1W more that makes it better. I would definitely go for EL84 or 6F6 if one can find it at reasonable price.
The full and truly cylindrical geometry of the original 6F6 makes it quite unique.....I love this tube as a triode and as pentode with local feedback.
If cost and space are requirements. PCL86 or 82 are unbeatable. No other tube required for a complete amp.
In triode mode at least 5W with with both of them are possible with 8K and running at about 280-300V plate voltage.
The PCL 82 was normally rated for 250V but in reality this is was due to the fact that it was operated with heaters in series in TV's. In a proper audio amp it can run just like the ECL82 at 300V.
I have run PCL86s of all brands for more than 15 years at 340V plate voltage in triode mode without 1 single failure, including the cheap Polamps (that now someone is selling like it were gold but they can still be found at low price....). Plain, decently filtered supply with no regulation.
With 340V, 6-8W are possible in triode mode. 6W are for the cheaper ones as they have generally lower mutual conductance and are less efficient.
Better with fixed bias.
It's not 1W more that makes it better. I would definitely go for EL84 or 6F6 if one can find it at reasonable price.
The full and truly cylindrical geometry of the original 6F6 makes it quite unique.....I love this tube as a triode and as pentode with local feedback.
If cost and space are requirements. PCL86 or 82 are unbeatable. No other tube required for a complete amp.
In triode mode at least 5W with with both of them are possible with 8K and running at about 280-300V plate voltage.
The PCL 82 was normally rated for 250V but in reality this is was due to the fact that it was operated with heaters in series in TV's. In a proper audio amp it can run just like the ECL82 at 300V.
I have run PCL86s of all brands for more than 15 years at 340V plate voltage in triode mode without 1 single failure, including the cheap Polamps (that now someone is selling like it were gold but they can still be found at low price....). Plain, decently filtered supply with no regulation.
With 340V, 6-8W are possible in triode mode. 6W are for the cheaper ones as they have generally lower mutual conductance and are less efficient.
Better with fixed bias.
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For 10W, PP, the UL taps 40% aren't right for the tubes that get you to @10W. So the best use of that tranny would be to just build a common EL-84/6BQ5 pentode amp biased for Class A and tie-off the UL taps. Then you can use a decent level of GNFB and still have some good power out.
You have aroused my curiosity here! Looking at the data the ECL82 seems to have the better triode, but ECL86 was more used commercially, like in the Rogers Cadet III amp.
Rogers RD Cadet MK 3 Stereo Amplifier Circuit Diagram and Operating Manual | valve-radio.co.uk
How did you find them for sound quality? Did you prefer the EL86 - was it more powerful or the same?