Amp Resto: '75 SF Twin Reverb w/ Altecs (Completed w/ Video)

Don Mogle · From: Round Rock, TX, USA

Here is another Fender Twin amp project that I'm going to restore. Thankfully, it's in pretty good shape as it is. However, it does need some cleaning, black tolex tears repaired, and general maintenance. This one is all original as opposed to my Pawn Shop Twin project.

HISTORY: This is a one-owner amp that was purchased in 1975 by the previous owner at a music store in Hawaii. He was in the Air Force and used it for gigs in the Marshall Islands. He returned stateside in 1978 and used it sparingly for the next 40 years. In October 2021, he had the amp recapped, other electronics replaced, new power cord, new reverb tank, and a few other things completed. It was virtually unused since the electronic work. He plugged it in to test it for his Facebook Marketplace advertisement.

The previous owner provided a copy of this service invoice to verify all the work completed. Jim Sliff: if you are reading this, I can verify the work was done.

Oh, the amp also came with the original footswitch and nylon cover.

WORK DONE TODAY: I tore into the amp and started my usual protocol of removing everything. I cleaned and scrubbed the cabinet with Dawn dishwashing soap, cleaned and polished up the hardware as best as I could, cleaned the grill cloth with Dawn and Windex, repainted the interior woodwork, cleaned the front of the silver faceplate after removing and scrubbing the control knobs, cleaned and lubed the pots, and cleaned up some dirt in the chassis. This made for a long day and I'm tired!

SETBACK: While removing the speaker grill from the amp, I noticed the cloth was stapled to a particle board wood support. After further attempts at removal, I noticed that the wood was cracked at the bottom center of the grill support. Why Fender used this cheap junk is beyond me...financial reasons I suppose. Now, I have to figure out if I want to repair this or build a new support out of plywood. Thankfully, Fender did staple this grill cloth to the wood baffle. Does anyone have any ideas on how to repair this grill cloth support? I was thinking of putting a stip of wood all along the bottom to stabilize it. Another thought was to dado the bottom edge and reinforce it with wood and/or metal. Any HELP or ADVICE is greatly appreciated.

OBSERVATIONS:

1. Yes, I know it weighs a ton with these Altecs. However, I have other amps to gig with. This amp will be used in my music room. Thankfully, it has wheels and I live in a one-story house.

2. I'm going to try and keep it all original and will not be doing any blackface mods to this amp. I thought of changing out the Altecs for a TT-12 and TC Furlong spec neo, but think I will just keep the Altecs in the amp for now.

3. I pulled tubes for safety reasons. The output tubes are new JJs. The input tubes were all RCAs which are original to the amp!

4. Note in the last picture below the velcro strips on the baffle are crooked and do not do a good job of holding the grill support in some areas. I will need to correct this issue.

Here are some more pictures for you viewing pleasure.

Bill A. Moore · From: Silver City, New Mexico, USA

On the plus side, the baffle itself seems fine! Silver Face I've seen with JBL's or Altec's are often broken.

Don Mogle · From: Round Rock, TX, USA

I know what you mean Bill. These Altecs are heavier than JBLs!

Ironically, I thought there was a crack in the bottom of the baffle. Upon further inspection, it turned out to be small strips or strands of glue. Boy was I happy when I realized this! I was mentally preparing myself for trying to force glue into a crack that turns out didn't even exist.

Whoever built this case decided to glue and staple the velcro to the baffle. I guess I will leave this alone rather than try to reposition some of these velcro squares.

Bill A. Moore · From: Silver City, New Mexico, USA

Here's the last Silver Face I had, ended up selling the chassis and cab to a builder in Albuquerque.

Don Mogle · From: Round Rock, TX, USA

Looks like yours cracked in the middle. JBLs? Do you still have the cabinet?

Bill A. Moore · From: Silver City, New Mexico, USA

No, I sold the cab and chassis to a guy in Albuquerque. I had already used the casters and cups, handle, and tilt back legs for another project. I sold/traded the JBL's last year, so I only have the tank left!
I do have a "cab" that a cabinet maker customer built for me too many years ago from "sustainable" small diameter Ponderosa Pine, I never did use it. Needs a baffle and rear covers. I just couldn't see covering it with tolex!

Don Mogle · From: Round Rock, TX, USA

Nice cabinet Bill.

I think a repair of the grill baffle is going to be difficult. Would you happen to know if Fender stapled and GLUED the grill cloth to the removable baffle?

Maybe I should stabilize the current crack and go to Mojotone for a replacement grill.

Bill A. Moore · From: Silver City, New Mexico, USA

I fixed one on advise of a friend by cutting the baffle flush with the cab, (jig saw), then installing cleats like a BlackFace. (One side was loose, and I reglued it back in), then cut, cover, and install a baffle.
I do have an extra Mojo 2-12 baffle that I removed to install a 1-15 in my Twin.

Don Mogle · From: Round Rock, TX, USA

Is it the speaker baffle or grill baffle/support? If you have a grill assembly, I'd be interested...

Bill A. Moore · From: Silver City, New Mexico, USA

Don, it's what you'd find in a BlackFace amp, baffle with spacer and grill assembled. 24 1/2 X 16 9/16

Don Mogle · From: Round Rock, TX, USA

Bill,

That looks nice. However, my primary need is for a silverface grill baffle.

If I had a blackface Twin under restoration I would be very interested. However, I don't know if a blackface amp restoration is in my future. Is this baffle/grill cloth combo made of plywood or particle board?

That said, PM me with how much you are asking for it? Thanks!

Don

Bill A. Moore · From: Silver City, New Mexico, USA

Don, it's a Mojo baffle, 1/2" ply with a 1/4" ply spacer. Your cheapest/best way would be to strip your grill frame, and use it as a template to cut a plywood replacement.

Jeff Highland · From: New South Wales, Australia

Yes routing a couple of grooves across the crack 3/4 of the way thru and gluing in some timber strips would be how I would fix it.
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Don Mogle · From: Round Rock, TX, USA

Thanks Jeff.

Tim Marcus · From: San Francisco, CA

if it were me I would replace that entire plywood cabinet with the dado baffle and frame with a brand new one made from solid Pine.

that would be the single largest tone upgrade you can make to that thing, plus it would cut about 5-6 pounds in weight

you can get that exact tolex/grill cloth combination and not have to worry about 40 year old hide glue coming apart after you clean it

Tim Whitlock · From: Colorado, USA

A worthy restoration project! But I'm wondering how it sounds. After trying at least a dozen speakers in my custom built Twin Reverb I finally settled on an Altec 418b. There is magic in the silky Altec top end that is addictive with a TR.

Don Mogle · From: Round Rock, TX, USA

Thanks Tim M. You'd be the one who would know about these things. Your knowledge, recommendations and advice is something akin to "words written in red!" I'll give your recommendation serious consideration. However, I already cleaned the cabinet with no adverse effects to the hide glue. It looks great right now even without polishing the tolex (which I will do anyway).

I looked on Mojotone's website. A replacement cabinet is around $500 which is pretty steep. As such, I will just use the existing cabinet to keep it all original. Besides, it'll be used in my music room so the difference in tone and weight just doesn't justify the additional cost. It's false economy. Thanks for the suggestion though. I might consider this for my Pawn Shop Twin if I can find the right deal somewhere.

Thanks Tim W. Appreciate the input. I should be able to get more bottom end out of two 12s (24" of cone pushing air) versus one 15. Paul Franklin told me this at one of the Dallas steel shows years ago.

*****************

Today I got a late start working on this project. I only had time to work on the cracked particle board baffle. Just to the right of the chopstick crack repair, you can see where part of the particle board ripped away after removing the velcro strip. The detached velcro strip still had a small section of particle board left on it. OK, here are some pics of today's work.

I cut a groove in the particle board with a drill and small bit since I have no router. The wood was kind of punky and chipped off a little bit. Maybe it got damp sometime during the last 48 years. I filled these voids with other wood which was actually repurposed chop sticks or coffee stirs.

I installed the metal strips for rigidity and to flatten out the wood splices. In 24 hours, I'll see if any further sanding is required. Thanks!

Tim Whitlock · From: Colorado, USA

Don Mogle · From: Round Rock, TX, USA

Don Mogle · From: Round Rock, TX, USA

Here's what I did today on this project:

1. Added another coat of black paint to cabinet for extra protection of the wood baffle and cabinet interior.

2. Cleaned the reverb bag and RCA connections on the new reverb tank (MOD). For all you originalists, I have the original reverb tank. However, I don’t know what’s wrong with it. The amp tech installed the two-spring MOD tank for some reason.

3. Cleaned the tube pins and sockets with 99.9% anhydrous alcohol, Q-tips and small brush.

4, Cleaned the speaker baskets, magnets, and cones. Thanks to Jeff Maxwell for the expert guidance and advice. I used a solution of Dawn on the magnets and frame that worked well. I then gently brushed the cones with a soft paint brush keeping the cones dry throughout this whole cleaning process. WARNING: DO NOT GET THE CONE(S) WET AS THIS WILL DAMAGE THE CONE(S) AND MAY CAUSE WARPING, ETC.!!

I also confirmed the cones are original evidenced by the 21000 number stamped on each of the cones (see picture below).

Here are some pictures of today's work:

Thanks for tuning in...

Don Mogle · From: Round Rock, TX, USA

It's done! I think it's one of the nicest '75 Twin Reverb silverface amps anywhere. Here are the pictures...

Conclusions:

It was a fun and worthwhile project. I'm glad it was in pretty good shape to begin with.

I opted to use a metal mesh screen for the upper back panel to allow better air flow and prolonged tube life. Of course I still have the original upper panel tucked away for safekeeping.

The previous owner gave me the original reverb tank along with a bag of original electronic components that were replaced in 2021.

I will test it out here shortly and report back to you. I may do a short video so you can all listen and give me your thoughts.

Thanks for tuning in and watching this fun transformation!

Don

Don Mogle · From: Round Rock, TX, USA

Deleted/error

John Ducsai · From: New Hampshire, USA

Looks awesome ! Whoa!

Don Mogle · From: Round Rock, TX, USA

Finally home with my recent Fender restorations...

The Peavey extension cabinets are loaded with 1201-8 Black Widows that sound wonderful with the PA 100. I'm in tube Heaven!

Don Mogle · From: Round Rock, TX, USA

Here is a short 3-minute video of the '75 Fender Twin. In this video, my signal path is from the guitar --> Sarno Freeloader --> Amp. I didn't bother plugging in the volume pedal. I used C6th tuning..

Next time, I will record this in landscape mode. Live and learn.

OK, enough talk. Here it is unedited with all the mistakes that I couldn't figure how to edit out.

https://youtu.be/nHTIxP3E9sg?si=1KJITlOdC9eYDc5S

Thanks! Let me know what you think about the Altecs and how they sound.

Don

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