SR Preferred Curcuit & Mods? PROPOSED SCHEMATIC ADDED

[JazzGuitarGimp]

Hi All,

A friend has asked for my assistance in building a Super Reverb.

1. Am I correct in thinking the AB763 is the preferred circuit?
2. Are there any universally accapted mods that we "just do" from the get-go (e.g. Replacing the 100nF couplig caps with 22nF when building a 5E3)?

Many thanks,
Lou

[martin manning]

Read through here for some ideas: http://fenderguru.com/amps/super-reverb

[billyz]

I don't think the ab763 super reverb needs any mods. I have used a 25k pot for the middle control, but the ab763 circuit is close to perfection. I'd worry more about the components, speakers, transformers, cabinet etc.

[billyz]

The nfb circuit can be modified to taste of course, or made variable.
I find the stock cap values work well. I redid the cap values in the past, like all 3's or increase , decrease uf, etc. stock is really good. Make one channel different. The 50kb switched intensity pot mod works. But stock with great speakers is very hard to beat.
I redid one with polypropylene caps and it was not as warm and rich sounding as the polyester caps. And those old ceramic treble and PI coupling caps just sound right. New ceramics not so much.

[pdf64]

I documented my preferred SR AB763 mods as AA1113, see http://s963.photobucket.com/user/pdf64/ ... ort=2&o=11
Whichever route you take, I suggest that you try it with the 10pF cap (between the 2nd and 3rd stages in the reverb channel) out of circuit.

[tubetek]

Related subject question-
When You build a Blackface Fender, what do You use / where can you get the brass grounding plate that appears in every BF I've seen? MOJO shows the blank chassis but makes no mention of the grounding plate. Would a ground buss serve as well / better?

[martin manning]

A ground bus would be better as long as it doesn't rely on the pot bushings for grounding to the chassis. With that assumption it is unnecessary to solder the bus to the backs of the pots, which can damage them and makes pot replacement difficult.

[tubetek]

Thanks, MM- I have some of the pot-tab ground lugs (thanks, RJ!) left over from a Rocket build; was planning on using a couple to string a buss wire across the back of the pots without soldering to the actual shells... sounds like a plan. I have a few builds under my belt, just never a scratch-built BF style.

[martin manning]

My preference is to support the bus from the pot solder lugs and ground it at the input jack end only (Dumble layouts, e.g.), or better yet do away with the bus altogether by running the pot grounds to the preamp board at the appropriate places. The pot housings need to be grounded for shielding purposes, and using a toothed washer on the bushing is adequate for that.

[Ed Chambley]

I have 3 SR's. All AB763. On one I did what Dave Funk used to do to them while in the tube amp buisness in nashville. It is disscussed here:

http://www.ampgarage.com/forum/viewtopi ... 14fd40750e

While I love an AB763, I must say this is a great modification.

[JazzGuitarGimp]

Thanks to everyone for all the great info. Much appreciated.

Billy, if you have time, and are so inclined to continue the discussion, I have a few questions regarding your reply:

When you are talking about tweaking cap value, what do you mean by "like all 3's"?

When talking about the old ceramic caps, which PI coupling caps do you mean, the ones at the input of the PI, or on the output of the PI? I am surprised to hear that Fender used anything but the blue molded caps for coupling and tone stack - except in the case of small (pF) caps.

-------

Right now, we are leaning toward a single-channel with HI and LOW inputs, and no tremolo. I will post a pre-build schematic when I get it done.

Thanks,
Lou

[groovtubin]

I don't think the ab763 super reverb needs any mods. I have used a 25k pot for the middle control, but the ab763 circuit is close to perfection. I'd worry more about the components, speakers, transformers, cabinet etc.

SO, what was that resistor Ken Fischer told you @? Very cool to have talked with him!

respectfully,. jim@Omegaamps

[67plexi]

Lou, I might be so inclined to sell this working Super Reverb chassis.
The last of the good CTS pots. I got the amp for the speakers.
Fender lovers may hate me I look at Silver Face and later black fenders as CTS pots and transformers. Dumble changed my life.


Steve.

[JazzGuitarGimp]

Thank you, Steve - but we're going to build this one from the ground up. It will be a good experience for both of us. And I plan on taking a couple of detours along the way:

- Single Channel with Hi & Lo inputs
- Mercury Magnetics iron
- No tremolo
- Variable NFB
- Possibly add a presence control
- Possibly replace standard BF reverb circuit with the 3-knob 6G15 reverb circuit
- Possibly build-in an active effects loop (D'L8r)

Cheers,
Lou

[JazzGuitarGimp]

Hi All,

Here is what I've come up with. I started from the AB763 Super Reverb schematic, and made the following additions / deletions:

- Removed the Normal Channel
- Removed the Tremolo circuitry
- Made the GNFB adjustable
- Added PI Balance pot
- Added individual Bias pots
- Replaced the BF Reverb circuit with the 6G15 circuit
- Replaced 12AT7 PI with a D-inspired 12AX7 PI
- Added a D-Style Active Effects Loop between the second and third preamp stages

(I know, it's not looking much like a SR anymore ) All comments welcome.....