Anyone build a SUNN 200S?

[reverendbk]

I am working on a bass amplifier which uses the power supply from the Sunn 200S: 2x KT88 in UL, and Dynaco transformers from Triode Electronics (PA60S PT, a431s OT, C354 Choke).

Question: Does anyone have experience using this choke with this PT? The C354 choke claims a 400VDC maximum rating, and ~200mA current-handling capability. In the schematic, the choke feeds the OT CT, and therefore must pass all the current in the B+ line. The 200S schematic shows 500VDC off the rectifier, already over voltage for the choke. It was the only Dynaco choke that triode had. I am concerned. So if anybody has built this thing, what has been your experience?

[loudthud]

Where are you getting that rating?

C354 Dynaco Choke Replacement also Sunn 3-10C MADE IN USA

The only thing I see here is 2500V hi pot test.

Are you planning on using a GZ34? With solid state rectification the B+ runs somewhere around 550V to 560V. Hope your filter caps can stand it.

[reverendbk]

Yep, there it is. I think I read that on another website after I bought the transformer package. Panic mode i guess, because the thing looked so small.

Yes I will be using a GZ34. Filter caps are 80uF 450V in series for ~ 40uF 900V handling. Preamp sections get 2x40uF in series. Should be able to handle it.

[soundmasterg]

The first stage in the preamp only sees around 440v max except at startup possibly so it should be ok with a 450v cap. The phase inverter stage sees close to 500v so a 500v cap would be warranted there. Other than those two, series connected caps for voltage handling are a good idea, but there is no need to series connect the preamp sections unless you're using 250v caps or just aiming for more parts count.

Also if you plan to use the amp for bass, I'd highly recommend a solid state rectifier or a Weber Copper Cap and larger filtering. It makes the bass tighter and quicker and sounds much better for bass that way. The only caveat if you use larger filter caps in that first stage is that you can not use the tube GZ34 anymore. But in these days of unreliable or very expensive GZ34's and some very nice solid state or Copper Cap type rectifiers, there isn't really any reason to go with the tube rectifier. My 2 cents...

Greg

[Gtr_tech]

Yep....screw the tube recto if used for bass.

[reverendbk]

Yeah, depending on the voltage situation I may go solid-state rectifier, as I have tons of big "Ultra FRED" diodes lying around, and this would be kinder to the PT also. If I do keep the GZ34 in there i will protect it with diodes (essentially just using it to drop voltage). So many options... Thanks for the replies, this thing is supposed to be on stage in less than two weeks!

[soundmasterg]

With a solid state diode setup, the amp will be about 560v on the plates and screens will be slightly less. As long as you use the filters I mentioned, then you would also be ok in the preamp. The GZ34 sags, which isn't great for bass, and the bigger problem is that it requires less than 60uf for the first filter, and new GZ34s probably need less. Whereas with a solid state rectifier setup, you can increase the filtering in the first stage to 220uf and get a tighter and quicker bass. Every bass player I've shown my modded 200S to with the higher filtering prefers that setup over stock. If you want to drop the voltage you can do that with a Weber Copper Cap WZ34 or WZ68, but I'd just put some FREDS in there and be done with it. My 2 cents anyway.

Greg

Greg

[reverendbk]

I got the amp built, and at least the power section still resembles the 200S. I put in an DC coupled LTP.

I attempted to bias it up w/o preamp tubes...
B+ is exactly as stated, 560VDC (SS recto). However, all the way down the B+ line at "V1", it is still about 524VDC! I even increased the 15K resistor in the B+ line (to PI) with another 33K. It made little difference. There's no way I'm putting any pre tubes in there! What gives?

On the schematic, it shows that even after the choke only, the voltage drops 20V and by the time it reaches the V1 cap it is down to almost 200 volts.

[loudthud]

Without preamp tubes, there is no current draw to drop the voltage. If you are using series connected caps with equalizing resistors, they will drop the voltage slightly, but it's the preamp and phase inverter current draw that causes a voltage drop across the 15K and 33K.

[soundmasterg]

Without preamp tubes, there is no current draw to drop the voltage. If you are using series connected caps with equalizing resistors, they will drop the voltage slightly, but it's the preamp and phase inverter current draw that causes a voltage drop across the 15K and 33K.

I was going to say the same thing but you beat me to it loudthud. Put the preamp tubes in there and the current draw from the tubes will cause the voltages to drop to safe levels.

Greg