EL84/6V6 5E3 Power amp question

[EtherealWidow]

First off, hello. I'm a bit new to the forum and I have a lot of questions about tube amps. Some dumber than others.

As the title implies, I'd like to build an amp with a 5E3 power section, but use a 6V6 (or 6AQ5) and an EL84 at the same time. (One for push, the other for pull) Why hasn't this been done before? Assuming that you have the proper value cathode bypass caps / resistors I don't know why it would be too much of a problem. I also imagine it would have a pretty big impact on tone.

Also, there must be a way to switch which tube would do the pushing / pulling. Would that also be a fine idea?

Thanks for any responses.

[10thTx]

It has been done before.

with respect, 10thtx

[EtherealWidow]

Well thank you! I guess I haven't looked in the right places then. Problem solved.

[d95err]

What is it you want to achieve with this type of poweramp? What kind of effect on the sound do you expect it to have? (Just curious...)

[EtherealWidow]

I've never built a tube amp before, so I just have some little ideas floating around that wouldn't be too difficult to accomplish.

I know that there are a couple of amps that use both 6V6's and EL84's (Egnater, Mesa, maybe some others) But I think they use the tubes in unison. With the Mesa Blue Angel I think both types of tubes are single-ended Class A and with the Egnater Rebel 20 it has 2 of each tube, so the different tube types are working in unison. I'm not aware of an amp commercially sold that uses an EL84 and a 6V6 working opposite each other.

I don't know if I'll accomplish anything, but I figure if I'm building a 5E3 power amp anyway and it's no extra work, why not try it out?

[Cygnus X1]

Seems to me to be a lot of extra circuitry and not for a beginner.
Independent bias, B+ supplies, etc.
Not to mention different output impedances.

I'd just try a 5E3 preamp with EL84 output if I was that curious.

[EtherealWidow]

Ah! So there are difficulties? From what I understand, the 5E3 is cathode-biased, is it not? And so different B+ supplies are necessary? Also, would different output impedances really be an issue? Sorry for all my ignorance.

[Cygnus X1]

With respect, you should build something proven first.
Then maybe start designing.

[EtherealWidow]

I'm absolutely going to be doing actual circuits first. That's why I started this thread. I just wanted to take something that already existed and maybe tweak it a bit to make something cool, but I wanted to make sure that it actually works. If it won't work properly with the way I'm planning on building the circuit and it's just too much hassle in general, I'd want to know. Now I can save this project for a later date after I get more experience. So thank you.

While I'm on the subjects of 6V6's and EL84's in the same power section, what about a 5F1 circuit? I'd want to wire up both sockets to be used, but only use 1 power tube at a time (obviously). Would that be fine to leave one socket empty while I'm playing?

[dass101]

I think it's easy to implement the asymetric PP power section, the only compromise I see is using the 6V6 at lower B+ so you can power both sides at the same voltage.
You will also have to use independent cathode resistors/capacitors, so you can tweak the current for each tube.
Both EL84 and 6V6 generally use 8K primary, no need for a custom OT.
I'm not sure though how this will affect the tone, but it could be a fun project.

[surfsup]

EtherealWidow, you can check out the P1x or HO amps at AX84.com which have "octal option" that you can wire in a noval and octal socket (both in parallel) and do exactly that - put in an EL84 or a 6V6/6L6/EL34 and switch between the noval and octal socket.

Complete schematics, etc are there.

[Paul Fawcett]

EtherealWidow, you can check out the P1x or HO amps at AX84.com which have "octal option" that you can wire in a noval and octal socket (both in parallel) and do exactly that - put in an EL84 or a 6V6/6L6/EL34 and switch between the noval and octal socket.

Complete schematics, etc are there.

Those are single-ended amps, not push-pull.

Parallel single-end designs are quite different in principle from having different tubes on the opposing sides of a push pull.

For push-pull, I'm not so sure that this arrangement will work so well, but you could certainly try it out for shits and giggles. You would probably want to set it up so that both tubes are biased to have fairly similar quiescent current draws to minimize DC bias currents through the OT. The main issue (or feature, depending on your point of view) is that the 6V6 and EL84 have rather different drive characteristics, with the EL84 being rather easier to drive than the 6V6. I'm guessing this would result in a lot of asymmetry and production of second harmonic distortion, which is normally canceled out in a push-pull stage. This could be desirable, although it will probably be accompanied by an increase in undesirable intermodulation distortion.

[Zippy]

For push-pull, I'm not so sure that this arrangement will work so well, but you could certainly try it out for shits and giggles.

Hmmm, I wonder whether it would sound more like shits or giggles? I'm guessing the former.

OP - Build a great 5E3 and go from there.

Or build the Eagle Supre (octal SE) if you want something more experimental (yet proven as a basis):

https://tubeamparchive.com/viewtopic.php?t=14349

[M Fowler]

Use no larger then 290-0-290 (580vct) PT. The EL84's cannot take as much plate voltage as a 6V6 so the PT at 580vct is about max use tube rectifier. Or go even lower such 275-0-275 you can go solid state recto or tube recto.

Use 8k primary OT your choice of secondary 4,8,16, etc. You can go as low as 6k6 too.

Use split load cathode biasing so each tube has it's own bias resistor/bypass cap.

Mark

[EtherealWidow]

Thanks for all the tons of info, guys. One more question. If I use a 275-0-275 PT so I can use a tube / SS rectifier, will I need to worry about bulking up the filter caps when using the SS rectifier? Thanks!