Fender red knob "The Twin" amp - thoughts?

[laurie]

Thank you!

It isn't quite finished. The reverb was sounding very thin. One of the transducers has failed mechanically and one of the two springs has detatched. Not repairable unfortunately, but easy to order a new one (about 50 Euro).

[laurie]

My 1989 red-knob "The Twin" resurrected. What was done....

• New output tubes.

• New output tube sockets with new screen and grid resistors.

• Weak V1 (12AX7) replaced.

• Failed V4 (12AT7) replaced.

• 10W failed/failing power supply resistors moved off-board to 25W resistors mounted on a custom fabricated heatsink outside the chassis. Burned PCB traces around where those resistors used to be cleaned and repaired (poor design, Fender - be ashamed). This part of the repair took maybe 10 hours and $50 in parts... "not commercially viable".

• All electrolytic caps replaced.

• All PCB mounted jacks replaced.

• All carbon composition resistors replaced (e.g. the 91k resistor in the phase splitter was measuring over 100k).

• All 1W resistors upgraded to 2W and stood up off the board.

• Failed reverb tank replaced.

• Crackling "standby" switch replaced.

• Old, dodgy repairs fixed (e.g. the hum balance resistors in the heater circuit).

• All pots and switches cleaned.

• Tolex repaired.

• Cleaned. And cleaned. And cleaned.

• Missing footswitch replaced with an era-correct spare two button switch I had in the junk box, with circuitry adjusted for this amp.

I swear this will be the last big Fender tube amp I'll tackle. About CAD$450 of parts. Not commercially viable to repair, hence the amp coming to me rather than going into the recycling. I wonder how many amps from this era are just junked because of the repair costs?

Anyway... Don't try this at home, kids!
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[The_Doc]

What an epic repair ! Meticulous work as always Laurie. I think one of the ‘house amps’ in the studio where I’m going tonight is one of these and I’ll see if I can track it down and plug into it. They do regularly test their amps so it should be safe

[bigtone23]

WOW!
For sure not a commercially viable repair, but cool that the amp lives on for a few more decades!

[laurie]

Thank you! Yeah heartbreaking to see these old amps so badly treated/maintained.

Happy to save them when I can.

[fuzzbuzzfuzz]

It all came full circle.

Coincidentally I atteneded a small jam session last weekend and it was the amp of the other guitarist. A Gretsch guitar, VOX wah, couple of other pedals and that. It was quite dark and jazzy but nice!

[bigtone23]

I like a lot of the features of this era amp, the series or parallel extension speaker jacks, the tube testing and bias access, the parallel channel input jacks...

[laurie]

I like a lot of the features of this era amp, the series or parallel extension speaker jacks, the tube testing and bias access, the parallel channel input jacks...

Agreed. With a few engineering tweaks (better resistor heat management...), and the addition of a "vibrato", it would be the perfect amp.

I have a JHS Tidewater that can sit in the FX loop for tremolo.

I decided to keep the original tubes in the amp - they are RUBY "RI" coin-base (soviet) 5881's. Indestructible mil-spec devices. They all test OK on the tube tester. They make the amp a bit darker and earlier power-tube break-up. I quite like it.

[laurie]

It all came full circle.

Coincidentally I atteneded a small jam session last weekend and it was the amp of the other guitarist. A Gretsch guitar, VOX wah, couple of other pedals and that. It was quite dark and jazzy but nice!

I'd be interested to hear what output tubes his amp has? If the originals, they might be Ruby "coin-base" soviets like mine.

[laurie]

In case you have an interest...
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