Peavey Classic 20 outputs change

[Randall]

Customer wants me to change his Classic 20 with EL84s to 6L6s. How feasible is this, and what would it entail? I see no V's on the schematic, or how to tell the PT rating.

http://www.thetubestore.com/lib/thet...-Schematic.pdf

[mozz]

First, you will be drawing more filament current, about 280ma more. Second, you will be drawing more plate current too. Can the trans handle that? Third, you won't be able to mount them on the pcb, very easily anyway.

[Randall]

Oh, I just now see they are EL84s, I was thinking EL34s. So, forget about that!

[Enzo]

How feasible is this

It's not.

Any chance the guy sees amps out there where you can swap 6L6 for EL34, and he is thinking EL84 is the same thing?

Do you have an operating C20 now with the EL84s? A few quick B+ readings will fill in the voltages. The heaters run on common 6vAC power tubes, and 6vDC on preamp tubes. The EL84s draw about 1.5A heater, while 6L6s would draw about 1.8A. Maybe not too much, but hard to say without testing.

The main problems I see are:
1. Where will you put the 6L6s? Is there room in the existing spots for two next to each other? You'd have to mount octal sockets.

2. Do you plan to gut it and build the same circuit on your own boards? The existing board will not accept an octal socket, and there is no room between board and chassis to fake it.

3. You would have to change the cathode resistors to get proper bias.

4. 6L6s will require a much larger signal to drive them than the EL84, so the output will be weak unless you add some sort of drive.

5. If he thinks it will double his output power, he is mistaken. The power supply provides the power, the tubes are just valves for it.

6. If he thinks it will be louder, even if you doubled the output power, it would only be 3db louder. For reference, the hi and low gain jacks on a million Fender amps like Deluxe Reverb or Twin reverb is 6db difference, so a lot less than that small difference.

7. I forget, is there space in the cabinet for 6L6s hanging down? Would they lay on the speaker frame? or bind on anything else?

That is what comes to mind as I sit here sleepy from a big bar burger and fries.

[eschertron]

All of that ^^^
The PI in the C20 is a cathodyne, so forget about getting any good 6L6 clipping. If he wants a clean, high-headroom output stage, he needs to mic it and feed the PA. There's a headphone out, I think, maybe that could be used to slave a larger amp?