Pulling tubes + using 6L6s in a Traynor YGL-3A

[AndyM]

So I found this old Traynor rotting away in the corner of my basement; it's got a great sound, but it's impossible to push it into overdrive without bursting an eardrum or two. So I pulled the first and fourth power tubes. It's been running fine for the past few days, and now it easily pushes into a marshall-esque crunch.

However, I'm getting a lot of odd-order harmonics at high volumes; I know this may be a problem with the filter caps (which I intend to replace soon anyway), but before messing with that I'd like to try changing the power tubes.

My understanding is that the amp should run on a 4 ohm load with all power tubes; as such, it should run on an 8-ohm load with only the inner two running (that's how I've had it set up, and it's working fine). Please correct me if I'm wrong.

I have two main questions: can this amp run 6L6s without modification, and should I set the bias different since I pulled the outer tubes?

[soundguruman]

You have to change the screen grid resistors to 470 ohm, hopefully 5 watt.
When you pull two tubes the voltage will go up. Then rebias it.
You may want a hotter bias, you may get less odd order harmonics.

[AndyM]

Thanks! I found a good pair of EL34s lying around, so I replaced the power and preamp tubes (short of one EL84 which I don't have a replacement for).

Still got the harmonic issue (sounds like a really bad harmonizer), even with a hot bias, so next step is replacing filter caps.