Hello, I am so hungry to build another power amp. I am trying to decied between an El34 PP triode design, or just a PSET design.
I am having trouble finding PSET designs for just 2 El34s Per Channel.
Will El34s running in PP in triode mode even go beyond Class A?
Would someone please direct me toward a good PSE design that uses 2 tubes per channel? I am dying to try this out.
Or as I am still a newbie, should I build a PP amp first before I try PSE?
I am lost! please help me!
-Moose
I am having trouble finding PSET designs for just 2 El34s Per Channel.
Will El34s running in PP in triode mode even go beyond Class A?
Would someone please direct me toward a good PSE design that uses 2 tubes per channel? I am dying to try this out.
Or as I am still a newbie, should I build a PP amp first before I try PSE?
I am lost! please help me!
-Moose
Triode, UL, or pentode, how you bias the tube determines the class of operation. Only Class "A" is suitable for HIFI when SE topology is employed. You have options when PP "finals" are used. IMO, "shallow" Class "A" operation has a lot going for it. You squeeze out a little more when peak power O/P is needed, while avoiding cross over problems most of the time.
2 tube PSE, I will tell you what I do. If the power supply in your existing amp is capable of supplying twice the current, you can do this. Wire a second (same brand) EL34 directly in parallel with the existing tube. The best way to do this is to use seperate stopper resistors for each tube. The cathode resistor now needs to be half its original value. The output transformer must now be half its impedance also. This will double the output power, so to take advantage of this power, you need a larger transformrer
Running two tubes in P-P allows the tubes to operate in class A, B, AB1, or AB2. A SE amp must always run in class A
Running two tubes in P-P allows the tubes to operate in class A, B, AB1, or AB2. A SE amp must always run in class A
I seriously doubt that, beyond a certain minimum threshold, more watts equal more oomph. My 94db/w backloaded horns sound more powerful when driven by a 1.5watt el84 set when compared to an el34pp, 30watts/channel. You could also try to connect the el34's screen with the Bill Perkins gizmo, this will give a lot more attack to the overall sound + tighter basses. A somewhat weak, smudged sound is inherent not in low-powered amps but a result of the conventional resistor triode-strapping method.
Simon
Simon
I don't agree. I don't think the threadstarter want to play music at louder volumes, I think he wants the music to sound more powerfull (correct me if I'm misunderstanding). At the same spl, one amp can sound more powerful than another. A 30watt amp putting out 1watt will not necessarilly sound more powerfull than a 2watt amp putting out 1watt. This being said, I do think that 3.5 watts (or how much does el34 set yield?) is on the low side to drive a 90db/w speaker, depending on the impedance load.
There's that famous phrase: If the first watt doesn't sound good, etc... Quantity won't solve a quality problem
Simon
Honestly, I always want more volume, however I always put quality first.
The EL34 in triode mode can put out a good 5 watts per channel, at the operating point I currently have it at. I am primarily looking for more headroom with the volume, so should I need to go to 11, I can. I almost want to build a 300b design, but they are so very very expensive (too much so for a college student), and I also think that 300b designs are a little over my head as a newby.
Ray_Moth, you seem to defend PP with your life! I like the passion, but why do you enjoy the PP design so much?
The EL34 in triode mode can put out a good 5 watts per channel, at the operating point I currently have it at. I am primarily looking for more headroom with the volume, so should I need to go to 11, I can. I almost want to build a 300b design, but they are so very very expensive (too much so for a college student), and I also think that 300b designs are a little over my head as a newby.
Ray_Moth, you seem to defend PP with your life! I like the passion, but why do you enjoy the PP design so much?
Hi alexmoose,
P-P designs have so many advantages. A less expensive output transformer and hum cancellation are big ones for me. I run mine in AB1.
If you are on any kind of budget, you can built a better P-P amp for the same money as an SE amp. I personally do not like lot's of 2nd order THD. Higher orders of distortion depend more on circuit design and the amount of feedback applied.
-Chris
P-P designs have so many advantages. A less expensive output transformer and hum cancellation are big ones for me. I run mine in AB1.
If you are on any kind of budget, you can built a better P-P amp for the same money as an SE amp. I personally do not like lot's of 2nd order THD. Higher orders of distortion depend more on circuit design and the amount of feedback applied.
-Chris
Yeah, I guess I'm beginning to sound like a cracked record! I just like the advantages of PP, provided it's nicely balanced. I'm not saying you can't get a good result with SE, just that it can be more difficult and expensive, especially if your speakers are not highly efficient (my Yamahas are quoted as 89dB).
PP opens the door to the more efficient class AB1, for cooler running and more power. It's easy to put as much NFB as you need around a PP amp to get sufficient damping - a different story altogether from SE.
I'm aware that some people deplore PP, class AB1 and NFB, especially SET 2A3 and 300B afficianados. However, plenty of people have voiced their appreciation of the finer PP amps like the Citation II - but maybe it's not the same people?
Alright, now lets take this one step further, What do you seggest as a simple PP design, I would prefer to use Triode-Strapped EL34s, however I am open minded. Simplicity is key for me, because I don't want to get in over my head. I am open to ideas, however I don't want to make a pp EL84 because it offers about the same power at my SE El34 amp. and EL84 Pentode configuration would yeild enough power, but Pentode mode scares me, because I have heard so many bad things about it.
-Moose
-Moose
EL34s in PP triode mode is a good place to start. Connect the plate to the screen, on each EL34, using a resistor from 100 to 1,000 ohms. This is a stopper to prevent parasitic oscillations and should be connected to the screen with as short a lead as possile.
Your OPT should give 5k plate-to-plate load. Use cathode bias, with separate 440 ohm resistor per cathode (bypassed with 470uF capacitor), if you have enough B+; otherwise you can use fixed bias (which is what I do, because my B+ is too low for cathode bias). Your plate-to-cathode voltage on the EL34s needs to be at least 400v, which means B+ needs to be at least 430v for cathode bias.
My favourite solution, which I have posted here before, is an all-balanced three-stage design consisting of 6SL7 LTP splitter with pentode CCS tail, coupled through step-networke to differential 6SN7 drivers, and EL34 triode-strapped PP output. The main advantages of the all-balanced design, using these particular tubes, are low distortion, good stability and negligible hum.
There are two NFB loops: local NFB from 6SN7 plates to 6SL7 plates (to optimise DC balance) and cross-coupled NFB from the EL34 plates to the 6SL7 plates. With the OPT outside of the loop and the step-networks between 1st and 2nd stages, there is no risk of LF instability.
The power supply, as usual, is a no-brainer (wait for the flames!)
Yes, I am aware that the PS is as important as any other section of the amp but, as long as you use good components with a sensible layout, it shouldn't be too much of a challenge. A good power tranny with plenty of capacity, thermionic or low noise SS rectifiers, a good smoothing choke and good quality smoothing caps should give the right results.
With EL34s in triode mode PP, you are very close to class A, so there isn't a great deal of difference between current demand at zero output and at full output. The PS need not be all that stiff and there is no special need for a choke input filter. A C-L-C will do.
This is not the simplest design, although it's not too complex either. For a really simple design, the Mullard 5-20 would be good base but you would probably want to use a triode for the first stage. A triode-connected EF86 apparently does the job well.
Hope that helps.
Your OPT should give 5k plate-to-plate load. Use cathode bias, with separate 440 ohm resistor per cathode (bypassed with 470uF capacitor), if you have enough B+; otherwise you can use fixed bias (which is what I do, because my B+ is too low for cathode bias). Your plate-to-cathode voltage on the EL34s needs to be at least 400v, which means B+ needs to be at least 430v for cathode bias.
My favourite solution, which I have posted here before, is an all-balanced three-stage design consisting of 6SL7 LTP splitter with pentode CCS tail, coupled through step-networke to differential 6SN7 drivers, and EL34 triode-strapped PP output. The main advantages of the all-balanced design, using these particular tubes, are low distortion, good stability and negligible hum.
There are two NFB loops: local NFB from 6SN7 plates to 6SL7 plates (to optimise DC balance) and cross-coupled NFB from the EL34 plates to the 6SL7 plates. With the OPT outside of the loop and the step-networks between 1st and 2nd stages, there is no risk of LF instability.
The power supply, as usual, is a no-brainer (wait for the flames!)
Yes, I am aware that the PS is as important as any other section of the amp but, as long as you use good components with a sensible layout, it shouldn't be too much of a challenge. A good power tranny with plenty of capacity, thermionic or low noise SS rectifiers, a good smoothing choke and good quality smoothing caps should give the right results. With EL34s in triode mode PP, you are very close to class A, so there isn't a great deal of difference between current demand at zero output and at full output. The PS need not be all that stiff and there is no special need for a choke input filter. A C-L-C will do.
This is not the simplest design, although it's not too complex either. For a really simple design, the Mullard 5-20 would be good base but you would probably want to use a triode for the first stage. A triode-connected EF86 apparently does the job well.
Hope that helps.
EL34 triode connected PP
You could use schematics of PP1C Power Amp that you can find at vacuum state http://www.vacuumstate.com/schematics.htm, please.
People that made this amplifier were very pleased.
You could use schematics of PP1C Power Amp that you can find at vacuum state http://www.vacuumstate.com/schematics.htm, please.
People that made this amplifier were very pleased.
Hi Alex,
Take a look at the design on my site under ST-70 mods, I built quite a lot of amplifiers based on this design and it was well received. It will give you about 16Wrms per channel and can use old dyna output transformers or the new dynakit transformers amongst others.
Seriously though if you really like your EL 34 SE amplifier there is no reason not to build another higher power unit, perhaps even based on the 6550 or KT88 with say a one electron output transformer.
I started with PP amplifiers and went to SE - I just find a properly implemented SE amp is more truthful to the music. And I started with speakers in the 90dB efficiency range.
Sorry to be running against the thread, but I felt an opposing opinion was warranted...
Take a look at the design on my site under ST-70 mods, I built quite a lot of amplifiers based on this design and it was well received. It will give you about 16Wrms per channel and can use old dyna output transformers or the new dynakit transformers amongst others.
Seriously though if you really like your EL 34 SE amplifier there is no reason not to build another higher power unit, perhaps even based on the 6550 or KT88 with say a one electron output transformer.
I started with PP amplifiers and went to SE - I just find a properly implemented SE amp is more truthful to the music. And I started with speakers in the 90dB efficiency range.
Sorry to be running against the thread, but I felt an opposing opinion was warranted...
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