I've been following the thread this week regarding the SB-220 saga, and it
must have cursed mine.
First of all, the amps been working 100% up to now. No mods have been done
and the 3-500Z's were replaced a few years ago with a pair of Eimac's.
I reached over and threw on the power switch, with the amp in the tune (low
voltage) position as I usually do. The exciter was in receive mode, as I
scanned around 20m to see who was around. I smelt the smoke at first,
looked over at the plate current meter, and it was sitting at .3 amps. I
didnt' get a chance to look at the grid current before I powered off the
Heathkit, but there was a faint sizzle noise also.
One of the tubes has a dark black line down the crease inside the tube, and
a light brown mark on the inside of the glass accross from it. The high
voltage wires that pass the filter caps inside a clear plastic tube, appear
OK, but the plastic is burnt as it passes one of the shorting resistors.
The rectifier metering board has a large burn mark under one of the diodes,
plus it looks a little black at the other end where the high voltage lead
departs.
I'll replace the tube, and was thinking of new caps and metering / rect.
board anyway.
What got it? Inrush current? Tube failure? Filter cap?
Just curious on the chain of events.
Gary Smith VE4YH
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