Hot Bias...OT damage?

[daz]

I asked this long ago, but as i recall i don't think i ever got a definitive answer. I had my pair of cathode biased EL34's (home build) biased very hot. I wasn't red plating at all, but any more and i'm sure it would have. i never had any issues and the amp sounded great that way. I then biased it much cooler after a friend's amp with the same circuit which i also built had the OT go south.

I want to bias it hot again and if i like it as much as i did then, leave it like that. I don't mind killing some tubes, but is there any way at all this could kill my OT?

[MWJB]

How hot was "very hot"?

What was the mA rating of the OT that went south?

You can't really have a definitive answer without definitive criteria.

It's more likely that the EL34 will die before the OT primary, as long as the OT can take 70mA or so. As plate current doesn't rise significantly on a hot biased, cathode biased amp you often find that in practice borderline/under designed OTs might last decades...look at the OTs on some old Danos that have been running at 60-70mA for years, they compare to 15W OTs in other amps.

I would bias it where it sounds best, a decent 40-50W OT should take 60mA or so in cathode bias. If your tubes only last a year or two, then fine, they don't cost that much & it's the tone that counts.

We don't know for sure that it was plate curent that killed your friend's OT.

[daz]

I don't recall where that amp was biased, but i do recall i had it right at what was max at the time. But i tried it last nite figuring i'd leave it if it sounded as good as i recalled.....it didn't ! I was wrong, and it sounds about the same. there may be a tiny difference but it's subtle if at all. so much for that idea...i put the larger resistors back in and will leave them in. At least now i know that i'm not missing anything. Thanks

[MWJB]

Cool. If the ears can't deduce any benefit to running more current than you have to, to get a good tone...then there doesn't seem to be any point in risking tubes & other parts (as you have realised).

The trouble with determining what parts like OTs can "really" take currentwise, is that you end up breaking them to find out. I remember a quote from Ron Haslam (GP bike racer in the 80's) "to find your limits, first you must exceed them"... a bit like learning how many beers you can handle as a teenager...hopefully, after a while you learn to go drinking with your pals, without barfing up your last meal & sleeping in a hedge :-)

But I digress...