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41-255 power dissipation reality check
#5

Just an update for future reference... I've finished the electrical restoration of this radio and made some measurements (all with 122V AC line) in the power supply section. Overall current draw was ~395ma on the line side. The rectifier output measured 272V (vs 265) and 196V after the filters (vs 180). When measuring across my discrete replacements for the multi section R61, the 150 ohm resistor was dropping 9V, so about 60ma current as expected and just a tad over 1/2 watt. The 33 ohm resistor was similar, 2V, so about 65ma, .13w. When I removed the original multi section, I found that in addition to the apparent flash marks and scorching, the insulating paper was burned away over that same section of the resistor body.
So far performance seems good as far as I can tell using only the loop antenna in my basement (I was able to receive CHU Canada at 3.333MHz last night...). I've performed an alignment and ended up making a chassis solder connection to the riveted mounting plate/ground connection for compensating capacitors 17 and 17A. It appeared 17A was way too touchy mechanically, and soldering took care of that.
Also, regarding the failed pushbutton power switch, I attempted to replace the switch body with a similar one from Lowe's as detailed in a post here on the forum, but ultimately there was enough mechanical difference that the switch only operated correctly intermittently. That may be because of production changes to the switch available from Lowe's or perhaps I missed something. In any case, when I examined the original switch, I found it had failed because the wire lead on one side was never soldered to the copper contact in the switch. I soldered new leads to the contacts and re-installed the original switch. Instead of using epoxy to hold it in place, I soldered two sections of wire into the remaining sections of the original mount rivets so the rivets would stay in place and to act as a guide for sliding the switch body on. When the switch body was back in place, I twisted the wires to hold the switch in place. Some time later, I realized I should have cut the heads off small machine screws and soldered those into the rivets so I could put nuts/washers on, but hey...


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RE: 41-255 power dissipation reality check - by jtiner - 08-28-2022, 11:11 AM



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