Hot PT's

a DIY, modified Mullard 5-20 monoblock design

Hot PT's

Postby Toobgeek » Fri Apr 08, 2011 4:38 am

Well, my amps are totally complete and up and running. However, I do have another questions (hopefully my last, right?). Anyway, after about an hour, the power transformers on both amps are hot. You can still hold your hand to them, but if it were just a little hotter, you would not be able to.

I doubt this makes any difference, but my household voltage generally runs about 121....and by B+ in these amps is running about 10-15 volts higher than what is on the schematic.

Thanks!
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Postby Geek » Fri Apr 08, 2011 5:02 am

Try a stock PA-060 for hot.... 60C. is the normal running temp =:o

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Postby Shannon Parks » Fri Apr 08, 2011 6:05 am

If you can leave your hand on them, that is A-OK and normal. I find that touch-for-just-three-seconds is about 135F (57C).

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Postby EWBrown » Sat Apr 09, 2011 5:20 pm

As you aren't leaving any fried skin stuck to them, or raising blisters, you're OK ;) (lol) [:)

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Postby DeathRex » Thu May 26, 2011 5:11 pm

I tested a unknown power transformer built into an amp and the ST-70. Both took about 4 hours to reach their top temperature. The unknown transformer got to 65 deg C, and the ST-70 got to 60.7 deg C using a Fluke 87 V with a temperature probe. I replaced the input capacitor, on the unknown transformer, with a 33uf from 100uf and got the temperature down to 58. I then tried lowering the AC input voltage from 121 to 115 and that only lowered the temp to 54. Lowereing the capacitor only lowered the B+ 5 volts. Lowering the AC input lowered B+ about 30 volts.
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