Restoring a 1964 Ampeg Reverberocket

Here is the restoration thread for my recent $100 pawnshop find, a 1964 Ampeg Reverberocket, model R-12-Rb -- which I'm slowly starting to decipher and reconstruct between other projects. At first I was elated to find this model amp for so cheap, having serviced (and drooled over) a couple of Ampegs previously, but at this drier-lipped stage I must say that this is the worst case of an abused and neglected amp I have ever come across in my shop (and I've seen some doozies!).

The amp reeks for one thing. Between the dirt, gunge, bilge, blown caps, brittle wire, and sad attempts by former abusers to "maintain" the amp (something tells me Dymo tape labels on the control panel and a microwave-over power cord are not exactly 'vintage correct') it's hard to decide where to start. (One of my friends commented: it looks like it's been dunked in beer.)

Rescuing stray puppies would be so much easier.

Anyway, here's some BEFORE shots of the amp and my inital stages of R&D before I get down to more serious (and dirtier) work. I'm going to have a bunch of questions and decisions as I go along, so I hope the good folks here will check in from time to time to offer bits of advice.

R-12-RB -- BEFORE RESTORATION:

Front of cab, with original grill cloth and logo, non-original generic vinyl covering:



Rear view -- The Pros: Original reverb tank and footswitch, mostly original circuit (except 2 resistors), some original tubes that work, functioning transformers

The Cons: spewing electrolytics, nameless mystery power tubes (possibly 7591s, to be determined), grey microwavish AC-cord with broken ground pin & WTF "safety ground" soldered to a cap clamp, chassis unwelded on one end, and oddball Phillips hi-fi speaker.



Top of the amp: The silkscreening wore off over the years -- or under the beers -- so somebody helpfully tape-labelled the panel (making sure they were nice and straight!) -- oh, and replaced the original knobs with what you see here.

Pro: The components and handle are original and in no worse condition than any other amp of this vintage.



Schematic on the back panel (which, unlike the rest of the cab, has its original blue check tolex). The schematic is dry as a bone and crumbly, so I carefully removed it and am going to re-draw it (See Step 1, below).

 

STEP 1:

Before beginning, I really want to get a handle on the circuit -- also so I know what parts to buy and can decide how extensively I'm going to rewire it. Since the schematic in the cab loses another chunk every time I touch it, and the only online schematics I can find are Joe Piazza's (for earlier tube-rectified iterations of the Rv), I've decided to redraw the schematic -- using the original, Joe's somewhat similar models, and the circuit board itself for guidance.

Here's the first stage of drawing -- up to the second triode of V1 (the same portion of the circuit in the above photo):

 

First question: I'm wondering the best way to replace the large 60/40/10/20 uF can cap, seen below. Fliptops sells a replica, but it's $47 U.S. and that's going to run me double that in CDN by the time it crosses the border. I have a JJ 40/20/20/20 can cap but it's too wide to fit without widening the chassis hole... and I'd have to run lugs in parallel to get the original values (and would still need one extra 10uF). Individual F&Ts, Nichicons or whatever else won't fit in the chassis -- I would need 4 of them. So I need a can for at least some of the original values. Any suggestions?




More to come...

 

Thanks. Yes, I'm a big Uncle Doug fan, and he has one about a 60s Ampeg (different model I think) I'm going to re-watch.

I removed the can last night. The 40uF lug was dead and the 60uF/10uF/20uF were all 50% off spec... definitely toast. For about 5 mins I considered gutting the can; I could fit a Nichicon or F&T 47uF and 10 or 22 inside, but that would still leave no place for the big 60uF inside the can. THEN, I discovered that the JJ 40/20/20/20 will fit. If I run 40/20 and the other two 20s in parallel, it will give me the larger values. Then, I'd only need to fit a little Nichicon 10uF/450 (which I have) and 25uF/25V in the chassis. If none of this works out, the JJ is just a bolt on can clamp, easily replaced, and I'll splurge for the Fliptop.

Yes, they are. Pots and wiring are original, so I'll do something about the labelling when I get around to reconditioning the chassis.

A couple of resistors were def. replaced, but to my eyes the coupling caps are original. I could be wrong. Here's a clearer photo:



The power tubes are 7591. I pulled them and you can faintly see the number from a certain angle on one of them. The other tube is identical. Once the amp is recapped and running, I'll check plate current, etc, to see if I can keep them. JJ, EHX and Tung-Sol all make replacements, so that's an option.

cheers.

 

Step 2:

I took everything apart last night and started testing components. The original Gibbs reverb tank is intact and functional. I lifted up the circuit board and it has a big moldy block of wood under it that Ampeg originally used as a spacer. The chassis is like a septic tank and the old solid core wires keep snapping here and there, so I think once I finish redrawing the schematic, I'm going to remove the circuit board, clean and test everything, then rewire it back in later on. Luckily the tube sockets and other major components are all good.







One other odd little thing is the amp has the wrong tube chart in the cab. The tube chart is for the R-15-R (Superbreverb I think it was called) that had the 15" speaker and a 7025 (not 6SN7, like mine) in V2.

 

Step 3:

Testing the windings on the output and power transformer for continuity. All windings are intact, so once they are cleaned up the transformers should be fine:



I removed the circuit board because a lot of the old solid core wire is extremely brittle and kept breaking off of components , there was a layer of bilge under and around the board, and there's too little room in the chassis to get at things properly. I diagramed all the connections first, and have the schematic to get it all reassembled later. Strangely, Ampeg used a wooden spacer under the eyelet board -- who knew?



The chassis cleaned up nicely, except all the silkscreening is gone and I need to figure out a way to label the controls later on. Any suggestions?





Broken chassis end riveted back in place:

 

Thanks for these suggestions, guys.

Yes, I've seen it before too. It's some type of resin they use to hold things in place. It's all over everything and a real pain. Agreed about lead dress. I'm almost done redrawing the schematic and will post it; going to make rewiring the thing much easier.

 

Here's the finished schematic. I re-drew this from the original dried-up schematic inside the back panel. Moved the output stage down a row to fit it in. Not sure how good the resolution will be uploading it here, so I've placed a link to the large version on Google Docs: https://photos.app.goo.gl/A7JEN5ZtzPcinbRX8

If any Ampeg afficionadoes spot any mistakes, let me know. One thing I can't figure out is the mysterious arrow labelled "K" next to the bias cap/ resistor that leads nowhere (it's like this on the original schematic; some oversight in the design, I think). I'll see if I can trace it when I get back to the amp itself.

 

Here it is on the schematic I worked from: "K" to the right of the cathode bias with an arrow as if keying to another part of the circuit (as letters A to F do quite clearly elsewhere). But there is no corresponding K anywhere else on the drawing:



Here's K again on the 90s Joe Piazza schematic for the R-12-R (the tube rectified version of the reverberocket... mine's the RB bridge rectified -- otherwise about 80% similar). Piazza has K keyed to the center tap for the heaters, which makes no sense to me:



Then, I found another fascimile of an original R-12-RB on the Watts audio page -- identical drawing to the schematic in mine but labelled differently. Here there is No "K".




I can probably figure out from the amp itself whether K needs to be there (probably an extra wire running from the cathodes to somewhere else); I'd just prefer to know why.

 

Good suggestion!