Anyone know what this cap is?

[Gaz]

http://www.vilo.net/suhr_badger/slides/b25.html

The little red mylar-looking one between the 2.7k and 100k resistors on the right side.

I've got the preamp worked out for the amp save for the FX loop and that cap. I was thinking it was a cathode bypass cap, but it doesn't seem like there's enough coupling caps on the board for the three gain stages and "tube-buffered" FX loop, so I think it may be a coupling cap, however it wouldn't make much sense since all the others are 150s.

From the pics, it's:

Input
150k/1.5k bypassed with 5-22uf
.047uf coupling cap
Gain control (1/2 of dual pot)
100k/2.7k (possibly bypassed)
Where's the coupling cap?
Gain control (2nd section of dual pot)
Serial FX Loop (doesn't seem like there's enough caps for this)
Plate-driven 100k/.1uf/.047uf/120p stack
Pre-PI master volume
AC30 PI
etc.

I'm really only interested in this for academic/boredom reasons so don't get all weird about it

[Structo]

Looks like a Xicon polyester.

By the way, John Suhr is a member here.

[John_P_WI]

Nothing to add here, but what a beautifully laid out and executed amp. It is good to see production level workmanship like this. John should be commended.

[Masco]

Nothing to add here, but what a beautifully laid out and executed amp. It is good to see production level workmanship like this. John should be commended.

+1

[BTF]

Agreed! I was not familiar with these amps, but the build of that amp is a delight to behold. My compliments to Mr. Suhr!

[Reeltarded]

I saw inside of the SL68 and it made me want to sit on his lap and hug his neck, not to mention they sound like everything you want to expect.

[Gaz]

I found out from the help of a board member that it's a 10n coupling cap. The FX loop is also not buffered, and is just a voltage divider coming off the 3rd stage, whichs explain the the lack of caps I noticed.

The one interesting thing about this amp to me is the 10k/2.2n conjunctive filter across the primaries just like the Carmen Ghia.

[John_P_WI]

I'm curious as to what is under the epoxy by the filter caps, I have a guess as this is a power scaled amp....

[Masco]

I'm curious as to what is under the epoxy by the filter caps, I have a guess as this is a power scaled amp....

The scaling is in the output tubes only. Curious- what would components under goop have to do w/ that?
Notice the dual gain has wipers tied together, I'm curious to what's going on there. Is this cascade or cascode pre?

[John_P_WI]

I'm curious as to what is under the epoxy by the filter caps, I have a guess as this is a power scaled amp....

The scaling is in the output tubes only. Curious- what would components under goop have to do w/ that?

One of the tricks to keeping the amp's tone consistent with power scaling is controlling the voltage at the preamp nodes. Without voltage clamps, preamp voltages tend to increase as the poweramp is dialed down unloading the PT. This amp has distributed filtering physically located within the preamp area and a very consistent tone.... just a guess.

[Masco]

Don't know if that's worthy of epoxy, but maybe...? Would you really require two clamps? Don't think the unloading would result in tonal change much at the pres. If so, it would be a positive change IMO.
Just noticed the gain wipers have coax braids tied, not the center conductors. Neatly done!

[John_P_WI]

Don't think the loading would result in tonal change much at the pres.

Hmm, a voltage difference of 25, 30, 40 volts at node 1 can make a very large tonal difference IMO and experience.

[Masco]

Notice above edit.

[Gaz]

This amp scales the output tubes only. I don't think the epoxy is hiding any components. In my experience, scaling the hole amp starts I sound really bad if you wanna get down really low volume levels.

[Masco]

Well, there's something under that goop, without a doubt. More than likely voltage clampers for the nodes as John_P indicated, probably something asked under KO'C's licensing agreement. The PS is the singe FET older style for cathode biased. Beautiful amp.