12AT7 in Univox U-255R runs scalding hot.

[fredcapo]

After weeks of working on solid state and hybrid amps, its a tubefest the last few days. Working on a neat Univox U-255R...the one with the 6973 output tubes.
Seems to just have bad plug and socket connections.
With all the contact areas burnished and tight the amp works pretty well. But the 12AT7 becomes scalding hot after only
20 seconds or so, while the other preamp tubes are almost cool. I am not sure if that is normal...

They use both halves of the 12AT7 for reverb signal out and in. The filament is 6.3 VAC (as the other preamp tubes) and Plate voltages are right on as per the schematic, 245V for the in (send) and 72V for the out (recovery) and the reverb sounds OK. The tube was swapped with another used 12AT7 w same results. The cooler 12AX7s are at plate voltages of 130 to 215. Thanks fpr any insight on this...

[Tom Phillips]

The U-255R runs the 12AT7 really hard. At least the half that is driving the reverb unit. I'm not surprised that any 12AT7 in that spot runs very hot. I'm afraid that it's just the way that amp was designed. "Scalding hot after 20 seconds" seems fast for heat up though from a cold start. Maybe you were exaggerating there. Really doesn't matter though because it's going to get really hot in that application. Many classic Fender amps use the two triodes of a 12AT7 in parallel to drive the reverb tank. It is always the hottest 12A_7 type in the amp. So hot that you can't grab hold and pull it out with your bare fingers comfortably like you can the other pre-amp tubes.

[fredcapo]

Tom - Thanks. I was going to say 30 seconds... As a longtime tube amp hobbyist and mostly digital career tech, I never grabbed a tube that hot. Just wanted to be sure there was nothing unusual happening there... I would know better than to try to grab a 6L6...