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Old 22nd September 2010, 11:42 PM   #1
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Default Hot power transformer in Simple SE?

The power transformer in my SSE has always run quite warm after a couple of hours of use. I recently changed my power tubes from EL34 to KT88 and now it's much warmer, if not hot. A crude measurement of the temperature shows about 100 degrees F. I expected the KT88 to draw more power but I wonder if this is too hot?

The transformer is an Edcor XPWR035. Cathode resistor ~450ohms.
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Old 23rd September 2010, 01:07 AM   #2
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If you can keep your hand on it for an indefinite period of time, then don't even worry about it. If you can keep your finger on it for ten seconds, then it's probably still OK.

Power transformers on Dynaco Mark III amps (among others) have been reported to run for decades at temperatures approaching 170 deg F.

I think yours is probably OK.
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Old 23rd September 2010, 01:42 AM   #3
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Old 23rd September 2010, 02:11 AM   #4
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No problem. A quick double-check of Edcor's specs shows the XPWR035 is rated for 200mA on the HV secondary, and 5 amps on the heater winding. That's plenty for a pair of KT88 in the Simple SE.

The only place where the XPWR035 might fall short is if you tried to use a 5U4 or other 3 amp rectifier. You've only got 2 amps on the 5 volt winding.

Quote:
Originally Posted by fandersen View Post
Cathode resistor ~450ohms.
That should work quite nicely for KT88, though I'd use something higher for the smaller EL34 tubes.

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Old 23rd September 2010, 02:51 AM   #5
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Quote:
Originally Posted by Ty_Bower View Post
The only place where the XPWR035 might fall short is if you tried to use a 5U4 or other 3 amp rectifier. You've only got 2 amps on the 5 volt winding.
I'm using a 5AR4 which I believe is rated at 5v/1.9amps
Quote:
Originally Posted by Ty_Bower View Post
That should work quite nicely for KT88, though I'd use something higher for the smaller EL34 tubes.
I can switch between resistors. For EL34 I use ~596ohms.
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