I take responsibility for red plating 3 tubes in the course of 3 years so the bias should be checked if moved around bumped ect:
The RI mullard el84 did not fair well at 370 plate volts at 42ma per pair , heat could be warping the grid support post i suspect and resulting runaway voltage hence red plating !
I just found amazing tones changing all the 12ax7 x 5 tubes.
Egnaters tube circuit diagram helped me find what each tube does, the EQ recovery tube socket adds or subtracts some gain so i put a Sylvaina long grey plate ax7 in that one and it is sonic bliss with no harshness .
Vintage tubes and a Sovtek 12ax7lps in the PI socket took all harsh tones out and gained it up to ridiculous loud.
For ever did i try the OD tube socket tube roll game.
Winner for rock was the Black long plate Sylvania but i prefer the Matshushita ax7 tube for good articulate crunchy chord blues rock stuff.
You may think this or that amp is all problems in what you read but alot is our fault and i never replaced any fuse in either Rebel 30 or Rebel 20 head ever.
No problems from either amp in 3 years ive had them.
I had the issue when you tap the front panel it was amplified , my effects send jack was not inserted all the way and is a switching jack type so it was on me again !
I do not trust RI mullard el84 or sino but luv jj 6v6 and el844- el84 and GE 6v6 tube set i have found used !
I wish you all the luck i have had as the Rebel20-30 were my first guitar tube amps !
I bought a bias probe for plate voltage and use the test points and Weber class A/B bias chart around 70% dissapation .
I think tube amps all need fans built in , cranking up when there best does get too toasty for delicate winding in transformers IMOP
I have bought about 75 12ax7 over the years , best new tube 12ax7 type may be the Sino Shugaung 7025 .
It has no harshness and good for bright amps also is smooth like a RCA black plate ax7 tube .
It will not breakup easy or fast niether !
Vintage tubes can be a pricey item !
The RI mullard el84 did not fair well at 370 plate volts at 42ma per pair , heat could be warping the grid support post i suspect and resulting runaway voltage hence red plating !
I just found amazing tones changing all the 12ax7 x 5 tubes.
Egnaters tube circuit diagram helped me find what each tube does, the EQ recovery tube socket adds or subtracts some gain so i put a Sylvaina long grey plate ax7 in that one and it is sonic bliss with no harshness .
Vintage tubes and a Sovtek 12ax7lps in the PI socket took all harsh tones out and gained it up to ridiculous loud.
For ever did i try the OD tube socket tube roll game.
Winner for rock was the Black long plate Sylvania but i prefer the Matshushita ax7 tube for good articulate crunchy chord blues rock stuff.
You may think this or that amp is all problems in what you read but alot is our fault and i never replaced any fuse in either Rebel 30 or Rebel 20 head ever.
No problems from either amp in 3 years ive had them.
I had the issue when you tap the front panel it was amplified , my effects send jack was not inserted all the way and is a switching jack type so it was on me again !
I do not trust RI mullard el84 or sino but luv jj 6v6 and el844- el84 and GE 6v6 tube set i have found used !
I wish you all the luck i have had as the Rebel20-30 were my first guitar tube amps !
I bought a bias probe for plate voltage and use the test points and Weber class A/B bias chart around 70% dissapation .
I think tube amps all need fans built in , cranking up when there best does get too toasty for delicate winding in transformers IMOP
I have bought about 75 12ax7 over the years , best new tube 12ax7 type may be the Sino Shugaung 7025 .
It has no harshness and good for bright amps also is smooth like a RCA black plate ax7 tube .
It will not breakup easy or fast niether !
Vintage tubes can be a pricey item !