1979 Fender Twin (very slow) restoration

Amps, Cabs, Speakers, etc
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laurie
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Re: 1979 Fender Twin (very slow) restoration

Post by laurie » Sat Dec 31, 2022 9:27 pm

Starting down the long restoration road.

Pulled the chassis out of the amp. Unbelievable amount of nicotine/smoke residue. This thing has spent 30 years in very smokey bars. I've cleaned the chassis with grease cutting kitchen cleaner, isopropyl alcohol, xylene, and grease cutting kitchen cleaner again. Still stained and smells. Only time plus the heat when I get back to Australia will remove it. Honestly, if it wasn't a vintage twin I would have just stopped and sold it "for restoration" by now.

- Replaced the damaged Standby switch.
- Replaced the missing Power switch.
- Replaced the damaged fuse holder.
- Replaced the old rubber insulated power cord.
- I broke the push-pull master volume pot when I was dismantling the amp. Fixed that.
- Replaced all the electrolytic capacitors.

I need to clean and lube all the pots, switches and connectors, re-tension the tube socket connectors, dig my bias meter out of storage, then power the beast up.

The fuse was blown and the previous owner had tried to fix it by wrapping aluminium foil around the blown fuse. I tested the power transformer and it is drawing only 300mA with no tubes inserted, so it isn't shorted (that was a possibility). One of the power tubes has pieces of the internal structure rattling around inside the tube, so likely the blown fuse is simply because of a failed power tube.
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Lots of lovely (if smelly) point-to-point goodness - showing locations of replaced LV caps.
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Twin - new LV caps.jpg
Twin - new LV caps.jpg (198.63 KiB) Viewed 5187 times
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New HV caps:
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Twin - new HV caps.jpg
Twin - new HV caps.jpg (342.17 KiB) Viewed 5187 times
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43 year old electrolytic capacitors - most of them starting to get a little puffy:
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Twin - old caps.jpg
Twin - old caps.jpg (346.7 KiB) Viewed 5187 times
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Pepe
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Re: 1979 Fender Twin (very slow) restoration

Post by Pepe » Sat Dec 31, 2022 9:39 pm

Wow, I hope you can rid of the smell one day. Great work so far!
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laurie
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Re: 1979 Fender Twin (very slow) restoration

Post by laurie » Sun Jan 01, 2023 2:13 pm

A couple of notes:
  • This is the 135 Watt version. Hence being so heavy. http://www.thevintagesound.com/ffg/sche ... _schem.jpg. These are extremely loud amps. I'm starting to wonder if I should keep it - too heavy and loud. I guess I'm not the only old(ish) fart that has had that thought! There is a reissue Super Reverb available locally. If I sold the Twin I would get enough for the Super.
  • This version has the "ultra linear" output transformer. I'll be interested to hear how it sounds...

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laurie
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Re: 1979 Fender Twin (very slow) restoration

Post by laurie » Sun Jan 01, 2023 9:59 pm

The amp is fully sorted. Holy crap it is loud! Testing it at full volume I needed earplugs. The pre-amp tubes were all OK. Power amp tubes were toast. Everything else seems to work OK.

Will clean the cabinet next and reassemble the whole thing.

I'm definitely going to move the Twin along to someone with a stronger back, and go and look at the Super Reverb tomorrow ;)

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Re: 1979 Fender Twin (very slow) restoration

Post by Pepe » Sun Jan 01, 2023 10:21 pm

Sounds like a good plan. I know what you mean. At some time we had a used Music Man Sixty-Five at our small music shop. Man, this beast was horribly loud! Too much for my taste.
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laurie
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Re: 1979 Fender Twin (very slow) restoration

Post by laurie » Mon Jan 02, 2023 1:26 am

So things are not going well. The amp worked perfectly on the bench but reassembled in the cabinet I looks like one of the power tubes has failed. Certainly it has destroyed one of the resistors across one of the power tube sockets.

So far I can see no reason for the failure... I'm thinking it is a bad tube which will suck because after I get the chassis repaired, I'll need to get another matched quad of tubes.

More to come.

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Re: 1979 Fender Twin (very slow) restoration

Post by Pepe » Mon Jan 02, 2023 8:13 am

:(
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laurie
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Re: 1979 Fender Twin (very slow) restoration

Post by laurie » Mon Jan 02, 2023 1:38 pm

One of the tubes has a failed heater - the wire is broken inside the tube. It is junk.

Not sure if that is what caused the issue - having one of the quad stop working. I have another quad in storage but it is truly annoying to lose $120 worth of tubes.

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Re: 1979 Fender Twin (very slow) restoration

Post by laurie » Mon Jan 02, 2023 8:27 pm

Amp is tested again with a pair of output tubes. Tested with the tubes in the two outer positions, then the two inner positions. Everything is measuring correctly, and there are no issues.

It was definitely a failed tube - it looks like the HT voltage arced across to one of the heater legs inside the tube. Blah.

Just need to dig a spare quad of tubes out of storage and everything should be good.

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Re: 1979 Fender Twin (very slow) restoration

Post by laurie » Mon Jan 02, 2023 8:29 pm

I ended up buying the Reissue blackface Super Reverb amp. I'll be selling the behemoth 135W beast.

The Super Reverb is a lovely amp. Not as "loose" and "subtle" as the old 1966 vintage blackface Super Reverb that I used to own, but it isn't bad at all.

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