200S schematics

[Greg_M]

While re-capping my 200s I noticed that on the schematics I have it shows two .25mfd caps coming off the 6AN8 tube, but I can't find any of that value in my amp. What's up with that?

[Jazz P Bass]

I take it we are discussing a Sunn 200S.
Can you upload a schematic?
The schematic I have I will attach.
Where are we talking on the 6AN8?

[Greg_M]

Yes the Sunn 200S and it is the same schematic you posted.
Coming off pins 1&3 on the 6AN8.

It was suggested that they are the Black Cats that are up by the KT88s, but mine are .1mfd @ 400v and I have a total of 3 of those
Mine is a '67, by the way

[Jazz P Bass]

Now I'm whicha.
0.25uf phase inverter coupling caps.
I see two.
Where is your third one.
That 0.25 value is pretty obsolete.
Nowadays it would be 0.22.
Link:715P22454MD3 Vishay/Sprague Polypropylene Film Capacitors

[Greg_M]

The third one (.1 @ 400) is coming off of pin 9 of the 6AN8
It's a Black Cat also

[Jazz P Bass]

Yeah that resistor & capacitor on the screen is certainly old school.
It helps with output linearity.

[soundmasterg]

You can still get new .025uf caps, but I think the only ones I know of are the Polyester version of the Orange Drop...225P's I think. I saw some a couple years back at AES, but I just looked now and don't see them. Solen makes a .27uf which is close, but a Solen will sound different than what is in the amps for sure. I wouldn't replace the coupling caps in the amp unless they are leaking DC to the following stage. The electrolytics need periodic replacement but not the coupling caps. The brown blob ones that Sunn used could stand replacement though. They usually still function fine but were lousy caps from day one with high ESR. These are the same as the dreaded brown blobs that Fender used in some of the Silverface stuff. Pretty much any caps are better than these.

Greg

[Greg_M]

Interesting they should change the values. I have been collecting pictures of the chassis on other peoples 200S' and it seems those black Cats (at .1uF) are pretty common. That's what originally made me wonder about the .25uF call out. The Dynaco Mk III has the same .25uF call out.

I never throw anything away (it's a curse) so I'll try the new caps I have and if they don't sound right I can put the old ones back in. The brown ones do look a little sad.

[Tom Phillips]

Interesting they should change the values. I have been collecting pictures of the chassis on other peoples 200S' and it seems those black Cats (at .1uF) are pretty common. That's what originally made me wonder about the .25uF call out. The Dynaco Mk III has the same .25uF call out....

SUNN started by using the power amp circuit published in the Dynaco transformer literature. The design was for HiFi and Dynaco would have allowed for good low frequency response. They would have been considered inferior if you couldn't claim flatness down to 20 Hz. (CPS in those days). This would have required higher capacitance coupling caps than are needed for Guitar or Bass amps. I assume that SUNN figured that out as their company evolved. The change to .1uF caps would have saved some cost, simplified their parts stock and maybe even improved the overall sound for the musical instrument amp application of the circuit.
Regards,
Tom

[Greg_M]

Very interesting

I played through a few Mk IIIs back in the day, mostly because they were really cheap.
I always like them because of their amazing power and low end.