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In Reply to: RE: pics, etc posted by vinnie2 on April 18, 2016 at 08:10:08
Aluminum housed resistors are designed to be mounted to heatsinks. Your resistor is using the cap as a heat sink. Get it a few inches away.
If I see it right, the cap is a 100uF 63V? Use at least a 100V cap and keep it cool.
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I think I will just go with the dog bones on all the cathode resitors. They seem to be doing fine. There was a 1/4" gap between the aluminum resistor and the cap, I thought that might be enough to allow for suffiient air cooling.
They are like the heating element in your electric oven. The radiant heat will kill, not just ambient hot air. Try 105C rated caps as well for longer life.
Thing is, if that amplifier is working at the shown operating point, the resistor should only be dissipating 1.5W. (41Vx0.036A), which shouldn't kill the capacitor right away even mounted like that.
Definitely something weird is going on here, I wonder if the B+ is way high
I have been checking voltages back and forth between the different sections and I am not happy with the amount of variance I seem to be getting. Need to search some more.
Some variation is normal but shouldn't be drastic. Begin by drawing a really accurate schematic, make a photocopy for the second channel and then record the DC voltage to ground at each of the tube terminals, the power supply points, etc. It can really help to zoom in on a Problem. One possibility is that those silver mica caps leak, causing the 45 on that side to conduct way too much and then putting a big voltage across the tube's bias reaistor and frying the capacitor. Some voltage checks with a digital multi meter or vacuum tube volt meter will get it all sorted out. The grid oh the 45 should be 0VDC.
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