Sunn ST-15 schematic

[MarkusBass]

I'm looking for Sunn ST-15 schematic. This is small, nice sounding amp. Some of the parts (speaker, handle) have Fender logo printed on it.

Mark

[DrGonz78]

Did you see this old thread?
http://music-electronics-forum.com/t37013/

I had an old Sunn Powered mixer from the mid to early 80's that I was fixing that had the fender PCB's and parts etc. Right around the time that Sunn was purchased by Fender I guess. Perhaps the old Squire Champ amp shares many similarities like Enzo suggests?

[Enzo]

Sunn has been a part of Fender for many years.

Look at the sschematics for the Squire Champ 15 or the Fender Sidekick 15, see if they look like your amp.

[MarkusBass]

Thanks Enzo, I think it matches Fender Sidekick 15. Here it is how it looks like inside:


Mark

[Enzo]

Somewhere I have a bulletin from Fender explaining several Sunn models are really Fender models under the skin.

[nsubulysses]

As far as I know Fender remade NO sunn amps and only made their own circuits with the Sunn name on it.

[Enzo]

I guess it is down to semantics. ANy amp that says Sunn on it is a Sunn amp. Did they "reissue" some old Sunn titles? Not far as I know, but I am not an amp fan.

The Sunn connection is no secret, any more than is SWR. Kinda like GM makes Chevys and Buicks both.

If you were responding to me, the bulletin was telling repair techs that the amps in the Sidekick line were also sold as Sunn models of different names, and the appropriate cosmetics. So there were no separate Sunn drawings for those models.

[nsubulysses]

Yeah semantics indeed.

FWIW the original Sunn Model T is 4xKT88 with ultralinear OT and two blendable channels (Bright and Normal), with a master volume. Sunn (Fender) Model T is just a regular 4x6L6GC output that's pretty standard in most Fender amps, and nearly identical part for part to the 90s red knob "The Twin" amp. It also has seperate clean channel and gain channel like most modern channel switching amps, FX loop, various line outs, etc. The original Model T had none of that.

Original Sunn 1200s was an all tube dual rectified 4x6550 amp probably doing 120W or so. The Sunn (Fender) 1200s is a tube preamp with all the bells and whistles and a mosfet driven output section that does 1200W at 2 ohms. This amp is also identical to the Fender Bassman 1200.

Also Fender made a 6x6550 amp to try to dip into the SVT market called the Fender Bassman 300. This amp is identical to the Sunn 300T, which is supposed to be a 300W "Model T" but sunn never made a 6x6550 Model T.

Anyway, it can be called many things, but it seems like Fender basically made the same amps they were already making (like GM made the same cars -- Camaro/Firebird, Sunfire/Cavalier, etc.), then put the Sunn name on them for some reason to try to sell them to two different markets. Or they just made whatever circuit they wanted and put the Sunn name on it, but to my knowledge Fender never faithfully reproduced a single Sunn circuit. Even though they borrowed the old names (Model T, 1200S), the amps were just Fender designs.

Why they did this in the 90s when Sunn amps were not popular and not NOW, is beyond me. Back then you could get an original Model T for like $300-400. Now they sell for $1500-2000 regularly on ebay

I bought a reissue Model T 10 years ago for $600 and now they regularly sell for $1000-1500. If Fender reissued their "reissue" model T today there would be many, many buyers.

[Enzo]

Well you have me there.

Yes, they make essentially the same amps in both brands for marketing. Just as GM makes Chevy trucks and GMC trucks that are the same. Music store A in some city sells Fender. They would be upset if Fender sold to store B across the street, so they make Sunn versions so store B has similar product to sell.

[nsubulysses]

Another one of our "I wonder what ever happened to...." posters wrote a lot about this Sunn/Fender scenario.

It is mostly in the "ultra nerd out" section -- Anchor States: Tech: Sunn Model T (reissue) schematics and discussion

According to him the reissue Model T is now known as the Fender Pro Tube Evil Twin. Oh well.

[Enzo]

I leave that stuff to the fans. You know, the guys who know how many stiches there are in the seams of an old tweed cab, or the number of grooves on a Fender skirt knob.

[MarkusBass]

Thank you all for interesting discussion. The amp is fixed now. I had to replace all (!) potentiometers. Apart from the low quality pots, the rest looks almost like new and the amp sound good (taking into account how small it is).

Mark

[g1]

I had to replace all (!) potentiometers.

Were the pots defective, or physically broken?
Some of those cheap Squier and Sidekick amps had the board supported only by the jack and pots. If the amp fell on it's face with a cord plugged in, the jack could get pushed in far enough to snap all the pots off.

[MarkusBass]

Thy were just defective - very noisy, sometimes slider did not have contact with the pot. So they were not broken but you may be right that the way the amp was assembled could make their life shorter . The PC board is supported by the pots and the power amp heatsink (visible on the photo in my first post).

Mark