36 Watt EL84/6V6

[ny_racer_xxx]

Anybody ever try doing a 36 watt with both EL84's and 6V6's? I'm thinking, hmm next amp, with both sets, and having a switch to have either or both. Kinda like having your cake and eating it too????

CR

[rjgtr]

I've done something similar with 6L6s and EL34s in a channel switching amp I built. It really is cool to use the 6L6s for clean sounds and the EL34s for dirty sounds.

I was thinking about building a 36watt with channel switching where the clean channel used 4 EL84s and the dirty just used 2. However, having 6V6s and EL84s together would also be cool, since the 6V6s would have more low end, but the EL84s have more bite.

[Alexo]

I think you basically would build it as a regular 36 watter, but use a 150 ohm cathode resistor for the pair of '84's and a 250 - 270 ohm resistor on the 6V6 cathodes.

Then you can use a switch to ground the grids of either set when/if you want.

There is a thread on this in the archives, look up the "black and tan" amp that someone built.

Only issue is the 6V6's take more signal to drive, so yo might want some sort of a voltage divider to hit them with a little extra signal over the '84's.

[keith]

I did that, and used a double pole double throw switch. One half of the switch gounds the cathode resistor of the desired pair, 6V6 or EL84. The other side of the switch is used in 6V6 mode and parallels a 47k resistor across the 47k PI tail resistor, resulting in ~24k to drive the 6V6 pair. I went a step further and added another switch to lift the cathode of the outer pair of tubes allowing for 18 watt operation. The result is 6V6 or EL84 in 18 or 36 watt mode. Makes for a high parts count though. If I had it to do over, I think I would use two EL84 tubes for the outer pair, 2 6V6 tubes for the inner pair, and switch between 18w EL84, 18w 6V6, or 36w all tubes combined.

[unchained]

Keith, do you have a schematic for what you ended with? I am thinking about doing the same thing in my next amp.

[keith]

Yes but it was done with Phils CAD package called pencil and paper. I will try to convert it and upload it today.

[unchained]

Sweet, thanks.

[rjgtr]

One way to compensate for the drive difference is to duplicate the circuit from the PI coupling caps to the power tubes twice. This lets you customize the grid leaks etc., for each pair of tubes.

[Graydon]

I'm moving this to the 36W forum room.

BTW, the new little amp from Egnator is an 18W design with both EL84s and 6V6s that are switchable. Rumour says they will be footswitchable in production. It sounds nice and it was neat to hear the difference between the tubes instantly. They had one at the Detroit amp show a couple weeks ago.

[jcny]

Sounds like they did their version of the Trinity SIIIv6 which has the switchable el84 / 6v6's. The chassis also has all of the locations for both sets of tubes.
Nice set up, I have one and I'm well pleased.

[LeeMo]

I too, have a Trinity SIII V6. I've thought about changing out the trannys and running it as a 36. The normal channel cranked thru 6v6's on a Tele is oh so 'lishous.

LeeMo