Hot mains transformers

[ToolGuyFred]

How hot do Paramount mains transformers usually run? For years I have been picking up my ParaSEX amps by the mains transformer and it has been warm but not too hot. When I went to pick up one of my son's Paramounts, they were so hot I had to put it down (and my hand was throbbing for an hour). This suggests 60+ degrees centigrade (140+ degrees in real money).

I am going to take measurements of temperature and power consumption to see exactly what I have but it was a surprise to find them so hot. Both amps are the same and are the 300B version. All voltage measurements taken at construction were within tolerance. These amps are the 240V version.

Can anyone tell me what the maximum surface temperature for these transformers can be without risking internal damage? I design industrial control systems for a living and am well aware that transformers can be run way too hot to touch providing they are actually designed to run hot (appropriate winding configuration and high temperature varnishes etc.).

How does this compare with the experience of other Paramount users?

[Paul Birkeland]

They do run quite hot, but still well under the maximum possible temperature of the design of the transformer.   Measuring the voltages in the amplifier will confirm that the power transformer is not being overtaxed.

[Paul Joppa]

I don't have my notes at hand, but I think when that design was done my target was a maximum winding temperature of 100C, which corresponds roughly to 60C surface temperature. All the internal components of the transformer are rated 155C.

The equations I have been able to locate for predicting temperatures are pretty crude, so I have used the winding resistance change to measure internal temperature, and use that to calibrate the equations I am using.

[Doc B.]

I have been running as many as 14 Paramounts at a time in my system for the past 7 years without any transformer problems. Not really much of any other problems either, aside from a few 300Bs getting long in the tooth over the years. They have been hotplugged mercilessly, left on for days at a time, and moved around often. The amps do get very warm and they have been extremely reliable in stock form.

[Adrian]

My Paramount main transformers are by far the hottest running chunks of iron in my BH arsenal (Crack, S.E.X 2.1, and EROS).
Like the experts have said already, I have had no problem running them for hours on end.

[ToolGuyFred]

Thanks, guys. That's very helpful.