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I constructed a filament supply for 4P1L in filament bias which resulted in the last cap emitting smoke. Hmmm......Voltages seemed to be correct. Goal was 27.5v at 620mA. Circuit was CLCLC, 25v transformer, Schottky bridge, 10,000uF cap, 280mH choke at 2.7A, 2,000uF, another choke the same, all in a different chassis. Then in the amp itself, 1,000uF at 35v before Rod Coleman regs. That's the cap that started smoking.
What's going on? Some interaction of chokes and caps?
I then used bench supplies to feed the filaments, and everything fine. Previously I'd used bench supplies for months in this amp.
Edits: 11/09/15 11/09/15Follow Ups:
Any chance the wrong wire is being tied to ground? Smoking occurred with tubes out of unit?BTW... are you using two caps in series in the PSU? To increase voltage rating. Just a thought. Many vintage guitar amps use this setup to increase voltage ratings.
Here's a photo of a Fender amp that someone did not set those two series caps in proper order.
Edits: 11/09/15
They might be compromised . You should replace them for your peace of mind.
Chuck them.
25V transformer will give you ~35VDC (25 * 1.414). The diodes will drop a small amount, but being Schottky, that amount is small. And if it is a 115:25 transformer and your line runs at 123VAC like everyone else's, then you will be over 35V.
Capacitor polarity? How do you have it wired in?
I can check it again, but polarity was fine before. In the amp and supply that is.
Just had an idea, though. I used a different connecting lead. Maybe I wired that up wrong.
Do smoking caps continue to work or do you need to chuck them?
You need to trash them, of course. Sounds like you've either got too much DC, or there's a lot of AC across the cap.
--------------------------
Buy Chinese. Bury freedom.
Checked everything and polarities look to be correct.
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