200S Power Tranny

[Rick Erickson]

I need a power transformer for a Sunn 200S that I'm restoring. Anybody here know where a suitable replacement might be found, or have a current production part # for say, a Hammond PT that comes close?

RE

[Tom Phillips]

Rick,
The specs for the secondary windings of the PT originally used in the 200S were:
410-0-55-410, 200ma; 5V, 3A; 6.3V, 4A. You will most likely need to derive the bias with a resistive divider since I doubt that many manufacturers include the bias tap in their off-the-self models.
HTH,
Tom

[Ray Ivers]

Rick,

Sorry about the price:

http://www.mercurymagnetics.com/page...og/MM_sunn.htm

Ray

[Tom Phillips]

WOW! That price would make me consider re-winding the old one.

[Tom Phillips]

Rick,
I found the Hammond model 378X power transformer. It's almost dead on for the 200S specs including the bias tap. $138.62 from Mouser. See http://www.mouser.com/catalog/627/1580.pdf
Tom

[Tom Phillips]

Hey Rick,
I found another source. Triode eletronics makes clones of the original Dynaco P-782 power transformer that Sunn used in the first 200S amps.
Check out http://www.triodeelectronics.com/mq782.html
The listed price is $99. Pretty good compaired to the MM $300 price.
What do ya think?
Tom

[Rick Erickson]

Wow - Thanks Tom & Ray. This is for a restoration I'm doing for Mike Lull, owner of Mike Lull's Custom Guitars in Bellevue, WA. [www.mikelull.com The original transformer was replaced with a Stancor P-8170 TV PT which was physically too large and was leaking wax all over the chassis from running too hot. I will look into the Dyna PT replacement, or the Hammond - one of those should work. I recently hot-rodded a 100S for Mike, who is a very good Bass player, using KT90 power tubes and a slightly modified preamp circuit. A customer saw it in his shop on top of a 200S cabinet and gave him the 200S amp to match his cab..

RE

[soundmasterg]

I've heard some very good things about the Triode Electronics transformers. If I had to replace the one in my 200S, that would be the first place I would go.

Greg

[Rick Erickson]

I've heard some very good things about the Triode Electronics transformers. Greg

That's the one I ordered. Will let you know how it works when I get it installed.

RE

[Amp Kat]

Just got two in for a Fisher 300 and they look real nice so I'll let you know as well.

[Mr. dB]

I need a power transformer for a Sunn 200S that I'm restoring. Anybody here know where a suitable replacement might be found, or have a current production part # for say, a Hammond PT that comes close?

That amp uses the Dynaco MkIII iron and power amp driver circuit, no? I'd look at Triode or Angela or Curcio or any of the other places that support Dynaco hobbyists.

Or just find a Dynaco MkIII and harvest it for parts. There's jillions of 'em out there, so the hifi boys won't get too upset if a few are lost to make guitar amps. For the price of one Mercury Magnetics power tranny, you should be able to find a ratty old MkIII and get the power, output and choke, and maybe even a working Cornell-Dubilier 4-section twist-lok cap, and the whole 6AN8A driver stage on a circuit board.

[Mr. dB]

http://cgi.ebay.com/Dynaco-MkIII-mk2...QQcmdZViewItem

[Rick Erickson]

I got the Triode PT. It dropped right in to the Sunn 200S chassis. I installed a 32x32/500V dual can where the original twist-lock quad cap was. This became the 3rd & 4th filter stages. I used (4) 100uF/350V caps in series pairs to make the first two stages of filtering - first stage-choke-2nd stage. This has worked well for me in the past and allows the use of a solid state rectifier plug in place of the 5AR4 rectifier for a stiffer supply and higher B+ voltage, which is nice for a Bass amp. The owner had me install a pair of EI KT-90 tubes and arrange the impedance taps of the OT for max. output. The amp now delivers 90W RMS into 8 or 4 ohms via the 16 & 8 ohm OT taps. The KT-90's seem to be comfortable running into half the impedance typical of EL34's or 6550's. It will be interesting to see if the transformers can handle the increased power, but the customer doesn't care if it blows up. I love customers like that.

RE

[Tom Phillips]

Rick,
Thanks for the update.
Glad to hear that it seems to have worked out well.
Tom

[soundmasterg]

Glad to hear that Triode transformer worked out for you Rick. On my 200S I didn't even bother with a can cap...I just left the stock one in place and disconnected it, because I didn't want to deal with cost in the future since discrete parts are so much cheaper. I went with slightly larger values too, and series connected the first two stages like you did, and I'm using a solid state Weber Copper Cap. It works and sounds great!

greg