Snubber Caps Question

Derrick111

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The Dubilier caps like the ones Neil pictured above that Marshall used are not electrolytic. They may be perfectly fine. They did use electrolytic caps sometimes, at least on some 100w models. While I suppose it is possible that a shorted snubber could take out a transformer, I have never seen this. The reputation that you mention of early 70s 50w amps blowing power transformers is as Neil said the result of the bias feed wire connected to the wrong way such that bias voltage is not fed until taken off standby. Why they did this on 50w but not 100w I'll never know. But they had enough troubles with this that they changed it by 1973. The area you call corrosion is likely from a power transformer going. Your power transformer may be an early replacement so it looks original. You see this mess in a lot of early 70s 50w Marshalls for this very reason. So not the snubbers from my experience, and only electrolytics generally need to be replaced, unless any others are out of spec or bad whic is quite rare. Don't take a chance with those bias caps... they are electrolytic and it seems kinda foolish to replace old electrolytics except for the caps responsible for your amplifier not going into thermal meltdown.
 

John Maheu

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Hi, I'd find some 2kv metallized polypropylene caps to put there.
Mouser, digi key, future... they'll all have them.
I had a musicman amp, and the plate voltage on those amps is north of 700 v, but low current draw on the tubes.

Anyway, the caps in the same position on the amp took a BEATING for 45 years or so.
Finally cooked up.

Old Mallory caps I think.

In that amp, you'd get a spike akin to a model t ignition coil or something.

Anyways, the 2kv, 3kv caps are cheap now.

Probably overkill on a Marshall, but why not?
Not cost prohibitive.

They are box caps. You will have to splat the legs and fit them upright, or if you have room lay em down.

If you want heat shrink the leads, and put a dab of silicone on the body if worried that they're not axial.


As far as electrolytic caps dying...yes. always.

But almost as regularly film caps die as well.

Marshall used those blue (polyester?) Caps all over the place in 90s Marshalls.

Those things are horrid, and are almost without fail faulty.

I'm on maybe Marshall 100 as far as repairs.

For me, ALL the caps except maybe in the tonestack or preamp (ic low voltage section)get replaced.

Any cap that has a couple hundred volts or more on it for 20 years, goes.

Low voltage electro caps get replaced, but low voltage solid / film caps can usually stay.

Last one I did was 6100, and almost every blue poly cap in the amp tested bad on ear meter.

Good luck.
Happy Thanksgiving if in the USA...or even if you're not.
 

John Maheu

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Hi, I'd find some 2kv metallized polypropylene caps to put there.
Mouser, digi key, future... they'll all have them.
I had a musicman amp, and the plate voltage on those amps is north of 700 v, but low current draw on the tubes.

Anyway, the caps in the same position on the amp took a BEATING for 45 years or so.
Finally cooked up.

Old Mallory caps I think.

In that amp, you'd get a spike akin to a model t ignition coil or something.

Anyways, the 2kv, 3kv caps are cheap now.

Probably overkill on a Marshall, but why not?
Not cost prohibitive.

They are box caps. You will have to splat the legs and fit them upright, or if you have room lay em down.

If you want heat shrink the leads, and put a dab of silicone on the body if worried that they're not axial.


As far as electrolytic caps dying...yes. always.

But almost as regularly film caps die as well.

Marshall used those blue (polyester?) Caps all over the place in 90s Marshalls.

Those things are horrid, and are almost without fail faulty.

I'm on maybe Marshall 100 as far as repairs.

For me, ALL the caps except maybe in the tonestack or preamp (ic low voltage section)get replaced.

Any cap that has a couple hundred volts or more on it for 20 years, goes.

Low voltage electro caps get replaced, but low voltage solid / film caps can usually stay.

Last one I did was 6100, and almost every blue poly cap in the amp tested bad on ear meter.

Good luck.
Happy Thanksgiving if in the USA...or even if you're not.
Sorry new here.
Don't see edit button / option. But right, whomever said to do the bias section is absolutely spot on. Do it now if you can. Don't wait.
FWIW, this 6100 came to the USA, via Holland, was in Brighton UK before that. A 230v model.

Lots of corrosion, and the bias trimmer was dead.
I replaced it with a multi turn pot (what I had on hand from studio gear repairs) and was able to dial it in. Replaced resistors and caps in bias circuit.

Thanks for letting me participate!
John
 

denrrou

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great, thanks!

i already replaced the daly filter caps with LRC filter caps of the same value and also replace both bias caps with 160v 10uf, the amps is running great now
 

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