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P.T.: How hot is too hot?

tubeampking

tubeampking

Chronic dabbler
Hello all. So I'm running a pair of Grommes LJ4 in my listing room...one I re-did the electrlytics just last nigt. The other is running with the original can. The can doesn't even get warm, but the P.T. does. Not burning hot, but hotter relative to the freshly recapped one. Any cause for concern? I do plan to recap the second one...just don't have the caps right now. As usual. any input is greatly appreciated...:scratch2::music:
 
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A general rule of thumb around here is if you can't rest your hand on the PT for 10 seconds then it's too hot. To get into a more useful answer we'd probably want to get into some voltage measurements to see what current is being drawn.
 
Surprisingly hot. A glance at specs on current production transformers (Hammond & Edcor) shows them using materials good for north of 100* C. For older stuff, almost certainly hotter than you can comfortably keep your hand on for too long. I recall reading somewhere that a lot of transformers are rated for operation at 160*F, which is petty toasty, while at the same time providing a decent margin if their materials are good for temps above the boiling point of water.

-Pat
 
These are circa '50s PP 6v6 mono amps. For that time period PT is probably expecting 115vac on the primary, maybe less. Depending on where the OP lives the measured voltage could easily be over 5-10% over that. We commonly get 123+ around here. Measure the secondary voltages. If they are over what's expected put a bucking transformer in front of the PT (or a variac). Assuming the rest of the circuit is in good shape that should keep the PT from running too hot.

(EDIT: I read elsewhere that the LJ-6 PT was 117v / 640VCT @75mA . Don't know if the earlier LJ-4 used the same PT though, can't seem to dig that info up quickly.)
 
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If it were mine, I would recap the 2 amps at the same time for best results.

Even though a transformer of today may be rated to 100 degrees C, most should not be run that hot for reliability.

The rule of thumb mentioned should be used as a general guide.
 
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