The amp was brought up slowly on a Variac. 30 minutes each at 75 VAC, 90 VAC, 100 VAC, and 120 VAC. No smoke or bad things happened. The voltages were all within specification at rated line voltage (120 VAC).
It turns out there was nothing wrong with any of the transformers (Whew!) and the tin diodes are fine.
I spent 2 days tracing down the cause of really low gain on the Normal channel of the Super Six, Turned out to be the .047 µF Paktron capacitor which leads to the Master Volume. ( I use an old Eico audio signal generator and multi-signal tracer, which traced the signal all the way through the preamp of the Normal channel, but it doesn't tell you anything about gain, unless you are really good at guessing. I could have hooked up the oscilloscope, but I'm too lazy,)
Anyhow, I eventually narrowed it down to the 0.047 µF cap. The capacitor measured no capacitance. Which is bad.
NOTE: Bad capacitors do not actually have "I AM BAD" written on them, which is unfortunate, because it would make troubleshooting a lot easier.
I replaced it with an identical Paktron cap that I had in inventory (that means I found it in a box after looking around for one for about an hour).
Normal channel now works great.
Also found that the Tremolo LDR was bad. The neon lamp was working fine but the CdS detector was fried. I thought I had a spare in inventory (see description of Inventory, above) but no luck. I ordered a replacement, should be here in 4 days.
I managed to de-warp the grill frame, and it sits flat on the cabinet now.
All the original RCA pre-amp tubes tested good on my TV-7 D/U.
The RCA blackplate 6L6GCs (2) test good and are perfectly matched. I will probably sell these on e-Bay to help pay for the restoration.
I bought 4 new TAD 6L6GC-STRs (my favorite new production 6L6s); they are well matched and sound really good. The 1972 Super Six has a "Balance" pot, not a bias adjust pot, so I converted the amp to true bias adjust. It's an easy modification that is often done on the Silverface amps. The original current bias on these tubes was way too cold (23 mA). After the change, I adjusted the bias to 36 mA at 460 Volts, which put the dissipation at about 60% - just right!
I installed the new optocoupler bug, and the tremolo sounds great.
I put the chassis back in the cabinet (first time in 25 years) and hooked up the reverb. All I needed to do was clean the RCA jacks - the reverb is flawless.
The amp is quiet at idle and the six speakers are all in perfect shape. The sound out of this amp is awesome; it definitely can make my windows rattle. The character of the Super Six is very "Fender". Lots of high end chime and a big, authoritative bass. I played it for a long time. Hard to stop.
The last part I need is the upper back panel, which I am having made by MojoTone. Should be here in a week. Then, it's done.
The amp was partially dismantled to be cleaned.
The cleaning procedure was as follows:
1. Red Scotch-Bright pad to remove rust and corrosion.
2. Vacuum up all the debris.
3. Liberal application of Krud Kutter to boards and etc.
4. Scrub with toothbrush and little paintbrush.
5. Corroded solder joints attacked with brass brush.
6. Repeat 3-5.
7. Rinse and brush with denatured alcohol.
8. Apply De-Oxit to boards, pots, and switches.
9. Re-assemble. re-solder all grounds.
I repaired the broken ground, touched up all the
questionable solder joints on the boards and the
pots and the tube sockets.
Rust on the chassis doesn't bother me too much, but the brass grounding plate was green from corrosion and there was rust behind it and behind the front nameplate. Ferric oxide doesn't conduct electricity, so I cleaned everything up to bare metal so there will be good grounding of the pots and switches and jacks.
I found that the main ground from the tremolo section was bad - the wire had broken and obviously wasn't making contact. I suspect I will find other things as I go along.
Filter caps are original and look to be in good shape. We'll see...
I repaired the broken grill frame and am now trying to un-warp it.
Vacuumed out about a half pound of rust, dirt, and miscellaneous stuff (including a small nail that was under the eyelet board).
Next step - cleaning the components on the board.
The Fender Super Six Reverb was a variant of the Twin Reverb, and was produced from 1972 to 1979. The amp typically produced 80 Watts (it was rated at 100 W) and used six CTS 10" speakers in a large cabinet.
I bought this amp locally from a guy who had purchased it new in 1972. He played it for a while until it stopped working, and then he took out the chassis and let the amp sit for about 25 years or so.
It is, frankly, one of the filthiest, most corroded amps I have ever seen. It is, however, completely original. It still has 2 RCA blackplate 6L6GCs that came with the amp when new, and it has a full complement of RCA pre-amp tubes that were also almost certainly original to the amp.
My intention is to restore this amp to original condition. It may take a while.
The chassis is rusty and dirty. The eyelet boards are filthy, warped, and the components on the boards are dirty and their legs are mostly corroded.
I suspect the power transformer is bad, which may have been the original problem. I also think the transformer took out at least some of the tin diodes of the rectifier section when it failed. Just guessing.
The tremolo bug is bad, the plastic cover is rotten and falling off the opto-isolator.
The speakers appear to be in good shape. The grillcloth frame is broken in three places and warped. The handles are missing, as are the chassis straps. The original owner says he has them somewhere, and he will get them to me when he finds them.
I think I will have to take this completely apart in order to clean it up. I will have to remove the transformers in order to test them. I will probably re-solder the boards and test all the components.
Got the upper back panel installed. Looks good. By the way, the Fender Super Six Reverb's upper back panel is exactly the same as a Twin Reverb back panel, except it is 10" long.
I installed a correct "F" cap on the speaker output jack, and I found a Silverface-era two-button footswitch for the amp.
The amp restoration is now complete. It looks well-aged and presentable, and the performance of the amp is really excellent.