72 Marshall caps

[Valvehead]

Working on a 72 Marshall 1959 . This one has 2 large metal caps right before the standby switch . They are .22 / 1Kv and dont appear to be polarized. Are these for noise suppression ? If they get leaky / dry up , will it cause hum / buzz / noise ?

http://www.kbapps.com/audio/schemati...shall/1959.php

[Leo_Gnardo]

Working on a 72 Marshall 1959 . This one has 2 large metal caps right before the standby switch . They are .22 / 1Kv and dont appear to be polarized. Are these for noise suppression ? If they get leaky / dry up , will it cause hum / buzz / noise ?

Those are film caps and don't fail the same way electrolytics do. But - they do fail with age apparently as I've seen some cracked looking and others entirely missing. My best guess is they're supposed to quench some of the buzz noise made by rectifiers as they phase between conducting & non conducting modes. Since I've seen amps lacking them function perfectly well it's apparent they are not entirely necessary. Why did Marshall install them then, they're not a cheap item. Ask Ken Bran. Maybe they were part of what was considered standard hi quality design back in the day.

FWIW Rivera places a 0.015 UF 1000V cap across high voltage secondary on their amp. I've seen several cases where that cap shorted and popped the power fuse. I replace those with a 1600V rated part, no more popped fuses. Same buzz suppression reason I suppose.

I expect we'll get a good engineering answer as to their purpose from other MEFsters very soon. 3 ... 2 . . . 1 . . . GO!

[The Dude]

Those are snubber caps to help keep the standby switch from arcing when you flip it. I would leave them be.

[Valvehead]

Those are snubber caps to help keep the standby switch from arcing when you flip it. I would leave them be.

ok-- thanks !

[Greg_L]

My 73 Super Lead has the same thing.