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Re: Transformer heats after amp is shut down.

10/24/2000 6:59 PM
mike kach
Re: Transformer heats after amp is shut down.
Your primaries are shorted, check your wiring, or replace a transformer  
10/24/2000 7:02 PM

how long was it on?  
It takes a while for the heat to propigate out from the core where it was generated.  
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10/24/2000 7:18 PM
Chris B

It was on for about an hour. How hot is too hot? It wasn't hot enough to burn my hand, but It was hot.  
Chris B
10/24/2000 8:31 PM
Gil Ayan

[QUOTE]It was on for about an hour. How hot is too hot? It wasn't hot enough to burn my hand, but It was hot.  
Chris B[/QUOTE]  
Chris, some transformers will get hot, and I mean HOT. It is easy to see why though, since they have to supply quite a bit of power: take say a 100W EL34 equipped monster. The tubes are biased to idle at about half power, so from the plate dissipation alone you have 50W that the tranny has to supply, and then... you have the filament supply with 1.6A @ 6.3 VAC is 10W, times 4 is 40W... Add a couple of 12AX7 filaments and you have 100W of power. All of that power, plus all the transformer losses, turns into heat...  
Another example, Fender Blackface Twin will get soooo hot that the faceplate will be too hot to the touch after a couple of hours of playing. In upside down designs like this, all of the tubes' heat it eaten by the chassis, so the transformer will will be bolted down to one hot piece of metal. In rightside up designs, like Marshall, tyhings are a lot cooler.  
So the thing is, mathematically one can see how the heat is generated in an amp. I have read more than once that it is better that the transformer dissipate that heat towards the outside (thus making itself extremely hot to the touch and making everything else aorund it - like the chassis - hot too) than that it keeps the heat to itself, thus damaging scorching the core.  
I built amps that get so hot it's not even funny, and I was concerned. Those equipped with EL34s got significantly hotter than the one with 6L6s. At first I worried, but it's been a year and I have gigged and recorded with the amps for hours at a time, and nothing has baked thus far, so I simply ignore the heat issue.  
A small fan goes a long ways though. A 3" little thing can make the power tubes cool enough to touch. Some, like Matcheless, would argue that the tone of the amps would suffer if the tubes were not hot, so they chose to not put fans in their amps.  
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