old electrolytic explodes

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ibvee

Well-known member
Joined
Mar 2, 2010
Messages
45
So today I fired up a Gates SA39 we just got in, for the first time. All seems well, tubes start to glow dimly, VU meter starts to move towards zero after a few seconds, so no alerts with me, guessing the power supply starts as expected. I open up the unit, to check some of the voltages. Next I grab my laptop to bring up the schematic, and check my email. In the meantime the smell coming of the unit is noticeable, but I expect it to be some dirt left on the tubes, as it's sort of the familiar smell when starting up an old unit after a while of downtime. Ten minutes, perhaps more, have passed and BOOM!

The 2 in 1 can electrolytic capacitor, the power supply buffer, explodes. Apparently a nice vintage paper in oil cap, as black oily stuff is all over the room, and a nice big pile of smoke fills the air.

The unit is fully original, has never been recapped as far as I can see. The only thing different from the manual is the 5V4 rectifier tube, which has been replaced with a 5R4. But as this tube is almost the same, and has the same pinout, I can't think of a possible way how the voltage may have been inverted. So assuming that this wasn't the case. Could it be that it exploded from old age?
 
I've had a huge radio interference suppression PIO cap in a tape machine explode ones. If I remember correctly it just shorted somehow because of aging material.
 
Yes age.  It's plug in for a reason.  Hopefully you're power trans is still okay. This exact scenario killed most originals.  I wouldn't use a different rectifier here either.  It's not PIO, being 20 mfd. 
 
It's quite a common occurance with old paper/oil electrolytics....Guess the dialectric breaks down over time....Just like some more modern electrolytics but with more spectacular results.......happy memories :)

 
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