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Twin Reverb Project

PostPosted:Fri Nov 27, 2020 8:40 pm
by TI4-1009
Last month my old bandmate from the 60s gave me his Silverface '76 Twin Reverb that had been sitting broken in his basement for a few decades. Although I've built an amp from a kit (BYOC Tweed Royal) I've been pretty intimidated by the discussions about Jerryfing or Alembicizing the Twin. The schematic has always looked like Mandarin chicken scratch and the discussions about "replacing the .047 coupling cap with mil-spec..." left me with eyes glazed over and wandering in the wilderness.

But with a lot of help from the gurus over on the TDPRI board I got the thing up and running! Three phases: 1- make it run; 2- upgrades needed for a 45-year old amp; 3- minor sonic improvements. I have an SMS/JG, so I really don't need a Jerrified twin at this point. I may eventually Blackface it (but it sounds pretty freekin good as is). And gloryoski- I can find my way around the schematic now and almost understand what everything is and does! Bucket List!

And- bonus- I have the option of running it through my Jerry rig cab loaded with JBL Ks!

Here's what I ended up doing:

Replaced screen and grid resistors and replaced two power tubes
Replaced all electrolytic caps
Replaced rectifier diodes
Added bias pot
Removed thermistor
Regrounded power cord plug
Bypassed convenience receptacle
Converted ground switch to NFB switch
Added pop resistor to standby switch
Replaced grid stopper and input resisitors
Replaced normal channel jacks
Replaced 8 slope and plate resistors
Replaced treble caps with mica
Replaced V3 and V4
Replaced V4 socket
Replaced V3 cathode resistor with a 2k2 and added a 22/25 cap
Replaced the phase inverter .001 and V4 .003 coupling caps with orange drops
Cleaned all pots and jacks
Rewired the footswitch
Vacuumed the cabinet, cleaned tolex with Dawn, 409, and Armor All
Removed and cleaned knobs and faceplate
Replaced chassis straps (one was completely rusted over)
Polished tilt-back legs

Here's a link to the help thread (many photos embedded):

https://www.tdpri.com/threads/diving-in ... p.1052053/

If you're headed down this path and on a steep learning curve like I was, two great resources are:

Uncle Doug's youtube videos (he's a great teacher):

https://www.youtube.com/user/Stratosaurus1/videos

And Rob Robinette's web page:

https://robrobinette.com/Amp_Stuff.htm

Re: Twin Reverb Project

PostPosted:Fri Nov 27, 2020 8:41 pm
by TI4-1009
Here's a few photos:

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Re: Twin Reverb Project

PostPosted:Fri Nov 27, 2020 9:17 pm
by Jon S.
Here's something I don't get. Today, such a premium is placed on super neat PTP wiring with a minimum of wire length. People pay small fortunes for such amps. Yet so many of the great BF Fenders of yesteryear have wiring that looks like rats' nests/spaghetti bowls. And they sound great!

Re: Twin Reverb Project

PostPosted:Fri Nov 27, 2020 10:47 pm
by Searing75
Great job man! So much fun refurbishing these old Fenders. Just a joy to work on.

Re: Twin Reverb Project

PostPosted:Sat Nov 28, 2020 3:04 pm
by TI4-1009
Jon S. wrote: Fri Nov 27, 2020 9:17 pm Here's something I don't get. Today, such a premium is placed on super neat PTP wiring with a minimum of wire length. People pay small fortunes for such amps. Yet so many of the great BF Fenders of yesteryear have wiring that looks like rats' nests/spaghetti bowls. And they sound great!
That's where they stuff all the "mojo". :lol: :lol: :lol: