6L6 tubes for Peavey Deuce?

[mhuss]

I have a Deuce on the bench, and the (apparently original!) 6L6 tubes are shot. These were an STR version, and when I started troubleshooting I figured out why - there's about 535VDC on the plates, a little less on the screens! Worse, there's one 400 ohm shared screen resistor for all four 6L6s (two have "bonus" 100 ohm resistors). :-\

Some of this is due to the 122VAC (not 115VAC) coming in, but still, modern power in the U.S. being what is...and the schematic shows 500v on the plates by design.

Are there any currently manufactured 6L6s that can survive under these conditions?

[Enzo]

It isn't voltage that kills the tubes, it is dissipation.

You have 535v on the plates, but what kind of current is flowing through them? See if that voltage drops when the bias is warmed up to a reasonable amount.

The two 100 ohm screen resistors are there to prevent unwanted interaction between the tubes. If you want, you could install separate screen resistors like any Fender, but these amps have been working now for 40 years the way they were designed.

[mhuss]

Good point. :-) I think if anything these were underbiased, only -49v on the grids.

Older Peavey stuff is usually serviceable, but on this model the cathodes are all solidly soldered to a large, broad ground trace. I don't have a Bias-rite type meter to measure, I guess I'd need to use the old 'OT secondary resistance' method. I need to get new 6L6s first, though. One is dead as a doornail, one provided a belated July 4th fireworks show(!), so I'd still like suggestion on what 6L6 works well for people.

[Mick Bailey]

When I get these old Peaveys they've usually still got their original tubes. More so than any other amp. I fit Sovtek 5881/6L6 and have never had one come back. Not sonically the best of tubes, but certainly amongst the most reliable under high voltage and/or high current. Branded up by GT, Engl, Mesa, National and lots of others. Probably the most popular OEM tube in recent years.

Bet all those small electrolytics are dried out in that amp, too.

[g1]

Agree with Mick. Enzo just posted a link in another thread, it mentions them being used successfully in many old Ampeg circuits that often run 550VDC plus:
https://www.tubesandmore.com/products/T-5881-SOVT

[DRH1958]

Yep, Sovtek 5881WXT. Had a pair come with a Fender Hot Rod DeVille from 1997 and still test at 90% and I would go for individual screen resistors as taking care of the screen is the number one priority in power tubes. Who cares if you lose a couple of watts in comparison for a little extra safety? As Enzo said, it's the wattage. Drop the screens so they are 5-10 volts lower than the plates, not just two or three. See if you can find some NOS from the late '90. Usually people go "oh Sovteks? Price them to move."

[Jazz P Bass]

I like to use the Sovtek 6L6 WXT's.

[Enzo]

If you don't have bias equipment, then power off and measure resistance from OT CT to a plate on an output socket. Now power up and measure voltage drop across that resistance. use Ohm's Law to calculate the current. Crude but effective.

[mhuss]

If you don't have bias equipment, then power off and measure resistance from OT CT to a plate on an output socket. Now power up and measure voltage drop across that resistance. use Ohm's Law to calculate the current. Crude but effective.

That was what I meant by the 'old secondary resistance' method that I mentioned - but I should have said 'old Primary resistance method'

Thanks, as always!