[Amps] AL-811H resistors

[Robert Groh]

The short answer is that it is never a bad idea to have higher power rating resistors - well, assuming you can fit them in and that you use the right type.  Generally the cooler something (electronic) runs, the better it's reliability (a rule of thumb for semiconductors at least is 2x lifetime increase for every 10 degC decrease in temperature).  So cooler is better.  The type of resistor (i.e. the construction - wirewound, ceramic, etc) certainly enter's into the picture.  The manufacturer's data sheet will give you guidance - maximum temperature rating, maximum full power temperature rating, etc. Mounting of the resistor will have some impact on everything.

Most power resistors carry their full ratings up to 75 degC and they usually do run hot.  I have one of those inexpensive remote reading thermometers (eBay, Harbour Freight,etc - $30 range)  (i.e. the gun type that you aim at the object) and that allows me to peek at component body temperatures - very handy for this sort of thing.

73
Bob Groh, WA2CKY




________________________________
 From: Tom Osborne <w7why at frontier.com>
To: amps at contesting.com 
Sent: Friday, February 14, 2014 2:09 PM
Subject: [Amps] AL-811H resistors
 

Hi All

I replaced the 4 caps in my amp, and found that one of the bleeders was bad.  Replaced it this morning.

After letting it run a while, I touched the 4 resistors and they seem to be pretty hot.  Is that normal with this amp?  I know that bleeders can get hot, but I'm more used to 1 big bleeder of 50 watts or so, not 4 at 7 watts.

Would it be better to replace the 4 bleeders with larger wattage resistors?  Thanks and 73
Tom W7WHY

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