Deluxe Reverb clone losing high end

[Fred G.]

My home-built ca 1999 Allen Accomplice has suddenly had a moderate decline in sparkle and high-end tone - kinda sounds like the tone pot on a guitar has been rolled back partway. Still plenty loud and punchy. I swapped out all the preamp tubes with known good tubes, with the exception of the 12AT7 in the reverb circuit (didn't have a spare handy) - no change. I have NOT swapped out the 6V6's yet, but checked the bias via the built-in test point jacks with 1-ohm resistors to ground, and the voltage drop is right around 20 mV for both tubes. The 6V6's are "used but tested good" RCA's. I've used two different guitars and cables. No change. Figured I'd ask around and get some other opinions and maybe save myself some time from going down some rabbit holes. Again, the amp just suddenly started sounding similar to a tone control on a guitar having been rolled back. I've tried testing for leaking coupling caps but I'm getting really tiny voltage measurements and don't know if they're even relevant - like .01 volts (with meter set to the 200mV reading, on the leg I unsoldered from the circuit). I don't know if these are phantom readings from the meter, or what. I'm not sure if I'm even trying this test properly. Thanks in advance!

[Leo_Gnardo]

I have NOT swapped out the 6V6's yet, but checked the bias via the built-in test point jacks with 1-ohm resistors to ground, and the voltage drop is right around 20 mV for both tubes. The 6V6's are "used but tested good" RCA's.

It's time you did then. Brand new output tubes seem to have a bit of extra "edge", that settles down after say 20 to 100 hours of use. Then after typically years of use, they start to sound flabby, don't "grab your ears" the way they used to. They might bias up OK, even produce expected power, just don't have that thing that makes 'em swing. For some blues players, they actually like that shagged-out response, but it's sure not for everybody. Bless them old RCA's, typically they just keep on going. But it does sound like it's time for a fresh set. Mostly I use JJ 6V6, but there again, they're not for everybody. FWIW New Sensor offers 6V6's they claim are based on RCA, sold as ElectroHarmonix and TungSol. Indeed the plates do closely resemble RCA, but I find they don't last well beyond 400V plate voltage. There are blackened-glass 6V6 from China and Russia, sometimes I find these work well and sometimes not so much. Or you could splash for some NOS RCA or Sylvanias and expect a good long run from them.

[Tom Phillips]

And please post only one thread on the subject.
Since this thread has received replies please delete the other identical thread you started 5 minutes before this one.

[g1]

Also I think you should not rule out the speaker.