can i use 6550's?

[tubeswell]

Yep you might be near the limit of your PT when you pump a heavy-metal chord signal through it with the amp dimed, (but then it might be rated somewhat conservatively) may be better to run them at 80-90mA or so idle if you are unsure. Its the heaters I'd be more worried about - those 6550 filaments draw 1.4 or 1.6A each (from memory)

[daz]

they're at around 75 now so i guess i'll just leave it and check the PT for heat.

[MWJB]

With an 8A heater current rating and 250mA on the B+ (Hammond 372JX) you won't have any problems with 6550 in cathode bias (plate current won't rise as considerably as it would in fixed bias), the tubes will most likely crap out before the PT.

Bias them to where they sound best to you...could be anywhere from where they are now to 100mA per tube? If you like them at 75mA that's cool....I doubt that you would need to bias them to more than 80-90mA in any case.

[daz]

Like i said i think i'll leave them. They seem to sound fine and i realized i still do prefer the EL34's after playing the 6550's for a few days. But leaving it where they are allows me to just pop them in whenever i feel like a change.

However, after all this about biasing to 100% in cathode bias i'm now wondering how my EL34's will sound like that. So i think i will try it and see, and that would also cause the 6550's to be closer to max. I think if i'm not mistaken, EL34's are something like 61ma at max, and i know mine aren't there. So i'll give that a try. Thanks.