02-15-2014, 02:54 PM
Would there be enough room inside the chassis for a transformer?
I decided to go with 25 W after checking the derating curve of the resistors. I don't know how warm it gets in the chassis after the radio gets good and warm, but the price and the size difference seemed insignificant to go with 25 W.
With a thin, even layer of thermal compound, both the side of the chassis and the body of the resistor get just a bit warm to the touch.
Most of the AC power in the radio goes to heating the filaments and the panel bulbs and in rectifying the B+. I doubt the B+ DC current varies much with volume, so the only variation would be the AC signal across the output transformer. I'm not sure how much variation that is with volume.
Just for fun I measured the AC input current on my 41-280, which doesn't have a dropping resistor in it yet. After about 10 minutes warmup, the AC input current was .402 amps regardless of volume.
I decided to go with 25 W after checking the derating curve of the resistors. I don't know how warm it gets in the chassis after the radio gets good and warm, but the price and the size difference seemed insignificant to go with 25 W.
With a thin, even layer of thermal compound, both the side of the chassis and the body of the resistor get just a bit warm to the touch.
Most of the AC power in the radio goes to heating the filaments and the panel bulbs and in rectifying the B+. I doubt the B+ DC current varies much with volume, so the only variation would be the AC signal across the output transformer. I'm not sure how much variation that is with volume.
Just for fun I measured the AC input current on my 41-280, which doesn't have a dropping resistor in it yet. After about 10 minutes warmup, the AC input current was .402 amps regardless of volume.
John Honeycutt
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