Caps for a 1971 Marshall

[C Moore]

http://www.schematicheaven.com/marshall ... w_1959.pdf

I have a 1971 metal panel 100 watt Super Lead. There are two 22uf/600V caps that feed right off of the power transformer, right before the rectifier diodes. I am assuming the 600 volt rating is necessary, but I thought I would ask anyway. These caps are not impossible to find, just expensive. So far Sprague is the only manufacture I see that offers this value. They are about $10.00 a piece, and not every body carries them. Not the end of the world to be sure. But it makes me wonder how often guys are ordering 500V caps, and if so how do they hold up? Last time I checked, the plate voltages on our amp were right around 505V.
Thank You

[billyz]

Your schematic does not show those caps. It does show the standard 32/32 uf can caps. They are after the diodes and I would definitely stay with the higher voltage rated ones. The voltage can and does surge at turn on. You can use dual 50/50uf here though as long as the voltage rating is high enough.
Measure your voltage right after the bridge rectifier and watch it when you flip the standby switch on. you probably won't even see how high it really goes.

I think what you have is this one.
http://www.drtube.com/schematics/marshall/1959u.gif

In that case forget what I said about the cap values, instead use these.

http://sozoamplification.com/royal67_purchase.html

Are you sure those are 22 uf and not .22 uf ?

[argonaut]

I believe those to be .22uf across the rectifiers.

[Roe]

leave those .22uf caps alone. they are there to remove ac ripple or noise.

[C Moore]

I could have sworn the caps said 22 and not .22, although they are pretty old and it may be hard to see the decimal. The amp is on the road for a few weeks, so I cannot take a look. You guys have more experience than I do with this stuff; that is why I asked. But these caps are about 10 x the size of any .22uf/630v cap I have ever seen. They are approximately 1" x 3.5". Would it be common to have such a low value filter cap? And just to clarify; I do not want to remove the caps, I want to replace them.

[doctord02]

Hmmm, that sounds odd. Wonder if it was serviced/replaced with something incorrect earlier in its life.

[billyz]

Those .22 caps are RF snubbers.

here are some for you.

http://www.westfloridacomponents.com/mm ... e_Code=wfc

Probably not absolutely necessary. But they could reduce some noise.

[mhuss]

I've worked on three 1970-ish superleads recently, and all have .22uF/1000v caps there. These are actually directly across the PT secondary and standby switch, and I think they're there to reduce popping when you flip the standby.

--mark

[CaseyJones]

Effin' Brit caps.

220 nanofards = .22 microfards. Unless I misplaced the decimal point. Which I do, all the time.

In the same vein... they shoulda used Whitworth fasteners in the damn thing. Quirky bastards!

[gearhead]

Effin' Brit caps.

220 nanofards = .22 microfards. Unless I misplaced the decimal point. Which I do, all the time.

In the same vein... they shoulda used Whitworth fasteners in the damn thing. Quirky bastards!

Got that. I always wonder why North Americans skip over nano and go directly to pico?

BTW, online converter for those of us (me-self included also) that misplace the decimal point:

http://www.unitconversion.org/unit_conv ... ce-ex.html

[Structo]

Here is a handy capacitor value conversion proggy for us with less math skills.

http://www.moyerelectronics.com/FreeDow ... ions12.exe

[angelodp]

I realize this is an old thread. Those .22uf snubbers are on some amps and not on others. If you have built one of these babies do you recommend as required?

Ange

[luix]

Without a resistor in series they only shift the oscillation towards the audio frequencies, it's a common mistake on snubbers or an industrial cost savage.

If the amp has no problem don't touch them, if you hear some noise you can consider adding a 100ohm (or so) resistor in series with those caps.

[angelodp]

My inquiry is more in regard to a new build and whether to include them. The Mojotone kit I have does not.

[luix]

Using snubbers is always an improvement because oscillation caused by solid state rectifier can add ghost notes and other noises that can be heard only in some situation and appears to be magical.

I can recomend you to use transformer snubber rather than diode snubber because UF5408 almost solve reverse recovery peak and SiC totally resolve it, capacitor charging peak are phisiological and the noise generated (if generated) can be attenuated with transformer snubber.
Usually 10nF to 22nF + 50ohm to 100ohm 2W series resistor are enough, if you want to be more picky you can read the attached document for snubber calculation:

snubber.pdf

PS, as my sign says, install a humdinger trimmer