Heat Dissipation?

[Willie]

I'm wondering about an aluminum chassis 4 el84 tube rectified head I have that heats up more than any other amp I have owned.
Doesn't resistance increase with an increase in heat? This must change the tone...also won't this shorten component life?...by hot, I mean:way too hot to touch chassis or jacks...can this heat be dissipated? A fan has not helped yet.....BTW it is a master vol, so at lower volumes it gets even hotter...thanks

[John Phillips]

Too hot to touch is way too hot. Some parts (especially electrolytic caps, but also insulation in older transformers) are seriously endangered by temperatures much above this. Electrolytics are usually rated up to 85¼C.

Do you know where the excess heat is coming from? If fan-cooling hasn't helped it doesn't sound like it's just the tubes - my guess is that the PT may be overloaded, and it's conducting heat into the chassis. This is really bad - if the PT is overheating, the core temperature can be far above even what the outside gets too.

How ventilated is the cabinet? Fan cooling won't do much good if you're simply circulating hot air inside the box.

[Willie]

Thanks John, the cab is pretty much a closed box, so that could be some of the problem, and it is "hung" like Fenders, so the tubes just heat up the chassis like a stove...I think this contributes a lot to the problem....it may be that it is cathode biased to run hot, and these sovtek el84s are cooking.....curiously, they have worked hard for almost a year in this amp, although I don't play this amp that often...the tubes are wearing down, but still OK , a PT problem: what should I look for, considering all I know is how to identify which one is the PT? Thanks...

[John Phillips]

Put your hand on the PT when the amp has not been on that long. If it's significantly hotter than the rest of the amp, it's the PT that's cooking the rest, not the other way round.