'74 SF Twin Reverb Rusty Restore!

[Filmersam]

Hi All!
I'm very new to the forum. Long time reader until now- I finally have something to contribute, and hopefully help people learn. Myself included.
I'm quite an amateur in the electronics dept. however quite mechanically adept and keen to get amongst it!
Here we have my 1974 Silverface Fender Twin Reverb. The 100w model w/ push/pull master volume.
I bought this amp around 6 months ago upon bad/false recommendations- she's pretty beat up for the price I paid. Recently I put fresh speakers in (2x Jensen c12k) a standard choice as I take it. The old guys have no marking, stamping or stickers whatsoever (they look old, have a large round black magnet) , and seemed to lack a lot of the detail and crispness I hear in the new Jensens.

Anyway, I opened it up not too long ago and to my shock and horror contained quite a lot of corrosion and rust, sticky residue everywhere (maybe some rust kill or CRC). It's a mess inside this amp. All of the components are all glazed over. It sucks.

Basically, I could flip this amp and get a fresh one quite easily- but I'm more inclined to go the DIY route and clean her up myself. I hate to think of the next buyer opening it up and feeling how I feel right now.

This afternoon I stripped the cabinent down- pulled all the tolex off as it was quite a shredded mess. The cabinent is in a poor condition too- all loose joints and gouges.

Hopefully I can gain some knowledge from this thread, and some advice on the particulars of my restoration. I know there's a lot of threads regarding this matter- and I'll be referring to them often.

Here are some pics.





Is it worth desoldering/disconnecting everything, clean everything/replace caps ect., prep the chassis and getting a re-zinc? There's no real rush to have it finished, I want to take my time and do it right, so I have a beautiful sounding Twin that will last me years.

[Filmersam]

The underside is in better condition.

[Chuck H]

"Is it worth it"? is a relative question. The amp is NOT worth the time, effort and expense as it is not one of the more collectible examples of that model. But if you enjoy a project and like to learn new things this is an opportunity to do both and end up with a very good amp!!! If it were mine I would do the restoration as a "BF" model. The BF (=black face) model is more desireable. Yours is a SF (=silver face) model. No reason you can't use the parts that are already there but rebuild it as the "better" amp model.

Your other option is to resign that there's too much work there and your not sure what to do. Example, the right speakers for that amp would have been the p12q's. A little more expensive and probably not any better. But a lot more "correct". If nothing is known to be wrong with the old speakers and the amp sounded better, why did you replace them? So, my point is that you could cut your losses. Sell the amp with an accurate description, take the hit and move on to a different, more carefully considered project.

[Filmersam]

Thank Chuck.
I've been contemplating a few things and I guess it was wrong to ask if it's worth it. 'worth it' implying that I would want to sell it in the future.
I guess I'm not really interested in changing the specs too much. (I'm not even sure if any mods have already been done) I like the way it sounds now, I just would like to make it more reliable, that rust is only going to get worse and cause me headaches!
Blackface amps are extremely rare in Australia- I've never seen one let alone seen one for sale. I did see a BF Princeton on eBay the other day though.
I think you misunderstood- I wasn't happy with the previous speakers. The c12ks have a lot more detail and crispness.
So let the desoldering begin? I may need a new fiberboard- this one is pretty damaged.
If anyone knows of a resource that stock SF parts, please advise!

[Chuck H]

If you really just want a loud guitar amp then you've got it. But I will say that I'm pretty experienced and "I" probably wouldn't try to rebuild it with the silverface wiring. The reason is that the silverface wiring is notorious for instability problems. Many of those amps age or need a repair that alters lead dress a little and then begin oscillating. The blackface wiring is easy to find as a layout drawing and is much more stable. Many players "blackface" their silverface Twin. That is, the amp is working fine but they want the tone of the blackface circuit and layout. So they make the extra effort to change it. But it's up to you.

I also wouldn't go with the stock black fiber circuit board. They suck. They are known to become conductive and require replacement. Some people say that it's because they absorb moisture and simply drying them will cure the problem. Well sometimes that works and sometimes it doesn't. It's not at all hard to make a circuit board. The tools cost a few bucks. as do the materials. You won't get the classic black look though. But IMHO the black is part of the problem. The black in those boards is carbon. Known as "lamp black" because it's made from soot. When there's enough carbon present and high voltage is applied conductive pathways can form and stay. I don't repair many amps. I design, mod and build. But of the half dozen or so black fiber boards I've seen, two were conductive to the point of needing replacement. But it's up to you.

[Filmersam]

That's some good advice. Cheers.
Well I want to make the amp more stable/reliable - rewiring it to blackface specs does seem logical.
Would you reccomend one of vintagefenderamprepair.com total overhaul kits?
Fender overhaul kits blackface your vintage silverface amp! | Vintage Fender Amp Repair
Thanks for info on fiberboards, I had no idea. I see some pre-made fiberboards here-
WATTS TUBE AUDIO | Twin circuit boards

[Chuck H]

That board looks fine. It can be had in "vintage brown" to sort of keep the look and it's available with turrets. Which are a little easier to work with than eyelets. It's expensive though. Still, making your own board would cost almost as much with materials and and any tools you don't have. But you'd still have the tools to make other boards. And THOSE boards would be cheaper. But if you don't plan to make more boards in the future...

I don't go in for the kits. Since you'll probably replace 90% of the components those kits will leave you hunting through electronics catalogs anyway. And it's just another mark up on the parts. There is a lot of good info on building the BF type circuit. I couldn't even find a layout for the SF circuit. So you'd basically be stuck looking at your photographs trying to figure it out!?! If your going to gut it, definitely go BF. It'll be tons easier and it's the preferred circuit anyway. Plus you can build the board complete with components and lead wires before you tear the amp apart to minimize down time.

I guess you'll need to go through the pots, jacks, switches and tube sockets to see what can be salvaged with cleaning. I would definitly focus on function over cosmetics for the inside. Outside should look fine with new tolex and a BF faceplate. Rusty tranformers, if they're not literally corroding away, can be cleaned with a stiff plastic bristle brush and painted with Rust inhibitive spray paint. If all the rust isn't removed that's OK. More important that you don't over abraise the laminates causing crosshatching and conductive contact between the laminates. A coat of paint will slow the rust to a crawl and that's about the best you can do. The chassis should probably be blasted and trated with a rust reformer type product. You may want to compare the expense to just buying a new chassis. With tolex, components, the speakers you already bought, misc. ends and bits you'll probably think you should have just bought an amp that didn't need fixing. So try to save wherever you can.

[Filmersam]

Great, well I'm pretty good at cutting costs, also i can budget over a longer time frame because I have another amp to use.

So looking at schematics, there's a few to choose from. It seems the popular choice is the AB763 circuit.
I'll probably go with this. As far as recycling parts out of the silverface, I'll trash most of the caps and resistors? Do you know if there's an accessible parts list somewhere on the net? I'll try to purchase my bits from an Australian supplier.

The power transformer has quite a bit of surface rust. I'll try some of that rust converter on all the spots, polish back the chassis and either paint it or get it zinc'ed.

Do you know of a faceplate supplier?

[Steve Conner]

Sounds like a fun project! You may be able to find suppliers by asking around the people at ozvalveamps.org. If you are struggling to find local suppliers, then one of those "blackfacing overhaul kits" might be worthwhile, since it should contain all the components you need. (I don't know why Chuck thinks it wouldn't.)

I see they offer a choice of Sprague Atom or F&T electrolytic caps. I'd go for the F&Ts, they have a better reputation for reliability.

Tube Amp Doctor sell faceplates, but I couldn't comment on whether the holes in the BF one would match up with the SF chassis.

[Chuck H]

That's a good point on the faceplate holes.

The reason I'm anti kit is that it only contains selected components and those have a double mark up. So the OP is gong to have to hunt for parts anyway. I just thought it would be smarter to source the parts as a whole without having to peck through and see what's missing. I can only speak for myself I suppose. But that seems easier. And it's less $$$.

[Zer09]

I'm guessing many of have been through this. As soon as I saw the OP it reminded me of the first (and last) vintage amp I bought on ebay for $200 about 6 years ago. Mine was a late 60's Bassman head. Looked great in the pics which were all exterior. Lesson number 1, don't buy an ebay amp without seeing chassis pics! When it arrived, the amp I thought would just need new caps and maybe a few other compnents was a total cluster f&%k. Someone had (unprofessionally) put in a 100 watt PT, removed the second channel wiring, turned most of the preamp socket holes into octals, and was running a long string of 6EZ5's in the power section. It worked, but barely. I took it to Dennis Kager's nearby shop and they told me to get rid of it. "Somebody tried to turn a Pinto into a Corvette" was the quote. I had only done a couple cap jobs on my older amps at this point and would have been in over my head. I put it back on ebay with pictures of the chassis and a description of what I was told at Kager's shop. It sold for $150 more than I paid. That money became my AB763 Bandmaster which was all original. A cap job later and it became one of my favorite and most reliable amps. In the end the guy who ripped me off actually did me a favor as I learned a valuble lesson and my own honesty paid off as I nearly doubled my money. Working on the BM also gave me the confidence to start building my own. At least Filmersam's amp is salvageable.

[überfuzz]

I have a friend restoring vintage cars. Crazy if you ask me. But amplifiers, go for it! ;-) Fun project.

What style or type of music do you play? There are more possibilities than TR-schematics.

[J M Fahey]

I'd start by not caring about "correctness" , "collectability", "resale value" or "mojo" and concentrating on having a good, solid , dependable amp for the next 20 years.
And *that* makes the effort worth it.
I'd start by stripping the chassis and sending it to have new zinc plating applied.
Cheap, easy, and the proper way to do things.
Ask them to apply a thicker than usual coat (cost difference is peanuts) , because these amps are often drenched in beer and worse (they'll believe you, when seeing it)
In fact, I'm *now* going to my Zinc Plater with 50 12" speaker frames, fresh from stamping and still covered in machine oil, go figure
As of the front plate, if a blackface one fits, fine; if not, keep the silverface one, it accepts "Blackface controls" of course, (it's still a Twin Reverb ) but you'll have an unused Master control ... big deal
I would buy a strip of fiberglass (best) or at least Pertinax (brown phenolic ) raw board material, drill and apply eytelets myself.
Easy (practice first on a small board) and you don't really need any machine at all, just a "hole marking punch"

of proper diameter and a hammer.
You first hit eyelet with the punch to open it, and a second hammer hit flattens it.
Real fast, but prectice on some scrap board first.
You'll get blackface layout easily.
Also add 4 or 5 standoffs to separate the board 1/2 " from the chassis; the Fender technology of screwing it down, with a fiber separator sucks.
And you'll have a *killer* amp.

PS: I forgot: apply some rust dissolving paste to your transformer covers, don't let any of it inside because itr's corrosive and conducts electricity, then wipe it off and to be certain, swab the transformer with clean cotton with some drops of alcohol.
Let it dry in the Sun and then spray it (or brush ) with rust preventer (or dual purpose) paint.
Hang it to dry while you wait for the chassis back.

[überfuzz]

As of the front plate, if a blackface one fits, fine; if not, keep the silverface one, it accepts "Blackface controls" of course, (it's still a Twin Reverb ) but you'll have an unused Master control ... big deal

But it is a big deal, both silver- and black-face = bitching cool. I'd leave it as is, some free mojo added just by the shabby looks.

Edit: Not sure everyone agrees but I'd go for a ground bus and leave the brass plate out.

[Zer09]

I would highly recommend putting a dwell control in place of that MV pot. I was intending to do that to my Deluxe Reverb for years and finally got around to it. I kicked myself for waiting so long to do it even though I've always had the pot. The reverb has become so much more useable for my tastes. No more zero to boing. My DR started life as a reissue so I had a hole on the back where the unused ground switch used to be. It would be nice to have it on the front panel but it's so nice to have either way.