SUNN 200s

[ernie_jr]

Has anyone when re-building a SUNN 200s ever tap the b+ from node A (before the choke) instead of node B (after the choke)?
If so, what were your results?
Thanks,
Ernie

[sluckey]

I have not done that but I'm curious... Why would you even want to?

[ernie_jr]

I noticed that on the Fender 135 w UL amp the first node was used, so just currious.
Thanks,
Ernie

[sluckey]

Did you also notice that the Fender doesn't even have a choke?

[ernie_jr]

yes I did, thanks, interesting since they used choke in the pentode designs.
Thanks,
Ernie

[PRR]

> SUNN 200s ever tap the b+ from node A (before the choke) instead of node B (after the choke)?

These are HIGH-voltage amps. The filter capacitor cost becomes an issue.

Sunn's approach was to use a small cap, giving high ripple voltage, and then a choke and another cap.

The voltage at the first cap is far from "smooth". My Idiot says almost 60 Volts ripple, over 11%. However at the second cap (after the choke) under 2V, under 1%.

Now you go over to Fullerton. The F-135 is actually a bigger amplifier. Moreover I believe Sunn was good friends with a winder, while Fender bought open market. And we know Leo was an accountant (not sure about CBS). Whatever, Fender designed with BIG capacitors and no choke. Works out to 26V ripple which is just barely 5% which is typically a cost-effective place to be.

If you move the Sunn plan over, you have a hair more B+ average but a lot *less* voltage in the dips. Max "clean" power will be lower. At high power the 120Hz buzz may be obnoxious. AND you paid for, and have been carrying, that large lump of iron choke. You have it, use it.

[sluckey]

Unlike the PT and OT, the choke in those old Sunns is quite small...

[ernie_jr]

Good reading, thanks PRR.Ernie

[billcreller]

I re-capped one of those a while back.  The bass player/owner loves that amp now.  It was left in a rental house & not claimed, so he go it for nothing !  Even the cab cleaned up great ....