Big Bottles With 600V on the screens

[tubeswell]

If you've had/got a screen issue, remember to check the screen grid resistors. You probably have a blown Rg2

[JD0x0]

Update: Fixed some cold solder joints, was able to get red plating to stop and now I can safely take some actual voltages and can confirm ~605 on the plates and ~600 on the Screens w/ the bias pot turned all the way down.

So, what's one more mod, especially one that makes the amp operate safely?

Because I'm not very familiar with the amp, not having built it, and just having received it. This amp was originally meant to put out 120 watts (For 1 pair of tubes) and that's a lot to ask from a tube that dissipates 42Watts, especially new production tubes. As I've already mentioned Leo Fender ran the hell out of 6V6's in some amps, considerably over spec, but due to the military grade tubes, they didn't have issues. Some of those amps, with new tubes, will even cook the new 14W JJ's. Many El84 amps operating over spec, as well, from the factory.

Why do all that work, when I can find a tube that works safely at those parameters?
The KT90 and KT120 seem like they could handle the duty just fine. Anode max and screen max are both above what the amp is currently putting out, and a hotter bias will pull the plates and screens down a little. The only thing I'd worry about with the EHX KT90 is the rated dissipation is 42W like the 6550/KT88, while original KT90 spec seems to be 50W, the Kt120 being 60W seems like it would run the most easily. The PT in this amp a monster.

[JD0x0]

If you've had/got a screen issue, remember to check the screen grid resistors. You probably have a blown Rg2

First thing I did. They look fine, and read fine on the meter. In all honesty, I could probably raise their value a bit though (250 Ohm) I also don't really want to induce too much of that 'squish' I assume neither did the builder, or they probably would've used larger values, too.

[JD0x0]

Found a completely ungrounded cathode on the driver tube. Seems to be in much better working order, now. KT120's are in, too.

[Phil_S]

Found a completely ungrounded cathode on the driver tube.

Well, real life if stranger than fiction! Glad to hear this is turning out for you.

[roberto]

Good to know it.
How is it sounding, with the KT120s?