How to flip between EL34 and 6V6 power tubes?

You might remember me starting a similar thread a few weeks back... that is, use a Ceriatone chassis to slowly build a clone of a Marshall JCM800 50W 2204... but it's going to have a hole in the rear of the chassis I need to find use for, so I was thinking of turning it into some kind of switch point to select between EL34 and 6L6 power tubes.

I think i've found a better solution - an ability to switch between EL34s and 6V6s.  EL34s for rehearsals and gigs, 6V6s for making a lower volume nuisance of myself at home.  From what i've read, this seems to be a very easy flip-between.  If it is doable, this is most certainly the course of action I will take.  It makes the most sense, as I have a bunch of new and NOS 6V6 tubes in my kitty already.

But again, I have to follow schematics in a monkey see, monkey do fashion.  I don't have the electronic intelligence to modify and adapt a circuit at whim.  This is where i'm hoping Group DIY can steer me in the right direction.


I've already bought the speakers and started building a 2061cx-style cab specifically for this head project, but i'm yet to commit to a Ceriatone, Triode Store, Mojotone, or Mouser solution for the head itself.  But living in Australia, Ceriatone seems the the most practical option (it's a close global neighbour, it's also the cheapest parts bundle, the cheapest postage option, and I like their chassis/faceplate aesthetic the most).

Here's the layout once again.  It's the half power switch that I want to refunction.




If you can help me out with my desired mods, i'd be much appreciative.

> i've read, this seems to be a very easy

I have not read that. Links?

Power output is mostly down to supply voltage and load impedance. Valves are just valves to allow the flow.

EL34 may run 400V 4K. 6V6 may run 300V 8K. That's why 6V6 amps are smaller. If you build for 6V6, and put EL34 in, you get 5%-10% more output: EL34 is a bigger valve but it is still about voltage and load. If you build for EL34 and put 6V6 in, the poor 6V6 will suffer.

Variable impedance is possible but awkward.

Variable voltage is now quite easy. London VVR is one such pre-engineered product. In a smaller amp, I was able to dial a key voltage from 300V to 30V for a 10:1 range of max power.

PRR said:

> i've read, this seems to be a very easy

I have not read that. Links?

Click to expand...

Google "6V6 2204" and you'll find what I found.  I guess the main caveat is they're using JJ 6V6s in most of the experimentation.