Is a 50v Presence cap too small for 100 watt amp

[talbany]

Reading the manual I see the 2 tube style. V2 as reverb driver (12 AT) V3a= reverb recovery and V3b the mixer (or mixer recovery) plate driven.

The Wonderland/Sterling is a 3 tube..1 tube for the mixer ,1 tube for recovery and 1 for driver. In general you have a 2 tube style ala Fender/SSS#005.The 3 tube style ala Wonderland/Sterling/#13/SSS #004 and 4 tube style, Tweed (SSS 001 and 002)
How it's mixed/tapped might change a bit however the basic topology (mixer/recovery/ driver) stays pretty much the same within the 3 variants.

Tony

[Guy77]

Thanks Tony you cleared up a few things I was not sure about! I thought all the reverb was being handled by V2 but its not. Its how you described it, 1/2 of the mixer v3 is actually connected to what would be the reverb tanks (red) RCA jack at v3b.
So that would leave 1/2 of v3 as the mixer. In the Wonderland all of v3 is a mixer as you mentioned.

Now I am wondering how they managed to mix clean and reverb with 1/2 a tube?

You can also see the blue wire from the reverb transformer connecting to v2b.
Interesting that they are using only 1/2 a tube as a mixer. I am wondering if that resistor coming off of v3b and going to ground is the 220k that usually sits on the reverb tanks Red RCA jack because I don't see a resistor on the RCA jack? I am wondering were the Reverb return pot connects here? I will take more pics on my next visit in several days!

G

[talbany]

Now I am wondering how they managed to mix clean and reverb with 1/2 a tube?

It's usually done (with a pair of mixing resistors) before the grid/ (input) of V3b, the signal is then recovered at the (output) plate via a typical gain stage..This helps recover any signal loss/ loading incurred during the mixing process. This is just a guess and would still want to see a schematic if you can do a quick one on the reverb.

Tony

[Guy77]

Now I am wondering how they managed to mix clean and reverb with 1/2 a tube?

It's usually done (with a pair of mixing resistors) before the grid/ (input) of V3b, the signal is then recovered at the (output) plate via a typical gain stage..This helps recover any signal loss/ loading incurred during the mixing process. This is just a guess and would still want to see a schematic if you can do a quick one on the reverb.

Tony

Thanks Tony that makes sense. I attached more pics from last time. If you look at pic titled Reverb Red RCA it gives us more info on the reverb setup. I am seeing a resistor with a cap tied to it coming out of the RCA jack. One of the pics also shows the Reverb Send pot on back wall.

I will take more pics when I visit in several days. So many questions now! I am tempted to build this. I knew this would happen LOL.

Reverb Red RCA (2).jpg

20210609_200603.jpg

20210609_200544.jpg

[Guy77]

Did you find out by any chance what are the values and the role of the capacitor and the trimmer on the pab relay board?

The value of the cap on the board is .001 uf 400v

[talbany]

OK..Finally having some time to look over the pics,here is what I think is going on.
V2a..1st gain stage (dry signal) for reverb, which then feeds the send pot on the back then to..
V2B. Reverb driver (or tank driver)
V3B. Reverb recovery other side of the X-former feeding a 200k mixing resistor (w/ dry side amplifier) into the relay board (or master vol)
V3A. Dry side amplifier

So just as the Manual states V2 drives the tank side and V3 is the mixer. Interesting that they only used one triode to drive the tank.
if anyone sees something different don't be shy

Tony

[Guy77]

OK..Finally having some time to look over the pics,here is what I think is going on.
V2a..1st gain stage (dry signal) for reverb, which then feeds the send pot on the back then to..
V2B. Reverb driver (or tank driver)
V3B. Reverb recovery other side of the X-former feeding a 200k mixing resistor (w/ dry side amplifier) into the relay board (or master vol)
V3A. Dry side amplifier

So just as the Manual states V2 drives the tank side and V3 is the mixer. Interesting that they only used one triode to drive the tank.
if anyone sees something different don't be shy

Tony

Thanks for your help Tony, that was great! I am going to be back in the amp tonight. If anyone wants me to confirm anything let me know.
A couple of interesting things I noticed about the reverb is:

1. there is a 10M resistor going from the grid of V3b (Reverb) to ground.
2. The 220k resistor that goes to ground from the RCA Tank out jack has a cap across it, never seen this before in a reverb setup.

I like the cleans so much on this amp I will need to build a version without Overdrive.

Guy

[sluckey]

Many of the Fender reverb amps have a cap across the 220K. The cap and resistor are mounted directly on the RCA jacks. The Twin Reverb AA270 is one example.

[mojotom]

Yes, Silverface amps got a 2n2 across the 220k. It does smooth out the reverb wet signal.

Do you like that amp more than a JM (clean side) ?
They seemed quite similar.

What about the OD with pre Reverb ?
You wrote about building that amp without the OD so I guess the OD is not so good.

Same tonestack as the JM ?

Thanks Guy for all the info !

[Guy77]

Hi Sluckey and Tom. Interesting info about the fenders using the cap on the Reverb tank Out jack.
I was going to build it without the Overdrive since I have other amps with overdrive allready, and this would make it quicker to build.

Hi Tom, I like this just as much as the JM and the JM is my favorite for cleans and I never thought I would play another amp as nice until I played this one.

The tonestack is very much like the JM except this has a 150k slope resistor I believe and JM has 100k. Will confirm tonight and let you know .

Cheers
G

[rootz]

Yes Tony, I do not feel shy to comment, but must stress that this is still speculating and judging from a couple of pictures.

I do not think there is an extra dry signal, like the dry mixer triode in the. I just can't see how that would be done, without first attenuating the signal from the preamp severely. Otherwise you'd put a pretty hefty signal on the mixer grid and just overdrive it. So, the master volume control might be in front of, but why would you boost after the master? What also seems strange to me is that your suggestion would also mean the full signal would go through (one of) the smaller looking coupling caps. While it is certainly possible, why would you want to use a small CC in that case and suffer loss of bass? On a side note, I think those small CC's are 2n2 or 4n7, but that is judged on their physical size.

With more pictures, I'm more than happy to trace the whole amp and make a publicly available schematic. Just really need to see the underside of those relay boards in detail, so the traces are clearly visible.

Oh and will definitely try a cap on the tank output. Looks like a smaller resistor value also tames the high end of the tank a bit, so 100k instead of 220k.

150k slope in a classic stack, much like #94 or #133 (IIRC). Shaves of some low end and makes, IMHO, a high plate amp more suitable for usage with single coil pickups.

[talbany]

Rootz
Thanks for jumping in!. That gain stage was difficult to tell where the shielded wire that feeds V3a's grid is coming from under the board That would help! Anyone?

Tony

[Guy77]

I will check v3a wire tonight Tony .
Just on the road today.
Guy

[talbany]

I will check v3a wire tonight Tony .
Just on the road today.
Guy

Cool thanks. Also 1 more thing while you are there?.. The shielded wire the comes off the RCA connection (w/220k) What triode does that feed?. That should do it..

Thanks

[rootz]

I agree Tony, very difficult to trace when you can’t see where wires are going. I judge these things based on the angle the wire makes at the socket/terminal strip, bend radius and what would seem logical to me. So my best guess is the rca socket (from tank) goed to v3a. V3a out goes to reverb return pot, return pot middle lug goes to v3b with the 10meg resistor. V3b out goes to the relay board. At least, that is what I can tell from the couple of pictures I have seen.