Recap Problem

[hossymandias]

Hey guys. I just recapped my 212-75. All electrolytics were replaced. The only discrepancies were the two 400mf 25v caps. I replaced one with a 420mf and the other with a 440mf. Also replaced both driver transistors.

When I powered her back on, I got nothing but a loud hum. One power tube began quickly red plating. I'm not sure how to proceed. Can I take out the power tubes and power it on without hurting anything? That way I could look at voltages without destroying my tubes. Any advice?

https://www.thetubestore.com/lib/thetub ... ematic.pdf

[Tony Bones]

Maybe one of those electrolytics got installed backwards?

[martin manning]

Can I take out the power tubes and power it on without hurting anything? That way I could look at voltages without destroying my tubes. Any advice?

Yes, I believe you can. Look for a little under 1V on C47 with TR1 centered, a little less than half of that on both of the transistor bases, and 22V on the power tube grids. You’ll need to have the power tubes installed to see where the cathode voltages settle, but maybe after checking the grids and base bias voltage you could power up just long enough to get a reading. They should be in the mid 50’s, I think.

[hossymandias]

I got it. One of the new transistors was shorted at the collector. All sorted out now. Thanks guys! BTW, I was able to pull the power tubes and power on no problem.

[martin manning]

Great!