1977 Fender Twin Reverb

1977 is the year the Silver-Panel Twin Reverb changed over from it’s mid-seventies design with the 100 watt/master volume circuit to the 135 watt Ultra-Linear output circuit. This must have been produced very early into 1977 because it does not present with the 135 watt UL topology. This one came into the shop in what I like to call “Frankenstein Condition”. It has had the entire Master Volume push/pull boost circuit taken out, had a Black-Panel faceplate put on, had the cab modified in strange ways, and isn’t really a pure Fender circuit - It resides somewhere between Black-Panel and Silver-Panel models. It was worked on many, many times. But the customer did not care about collecters value, they just wanted a reliable, bullet-proof, gigging amp and to not have to worry about taking a valuable vintage amp on the road. So that is what we did with this one. I did not return this to any one model or back to original condition. We just made it gig-worthy.

The amp was given a partial restoration to complete the previous one from 5-6 years earlier from a different tech. The quality of the older restoration (parts quality/technique) was actually good - which is rare - but there was a considerable amount of preventative maintenance left undone and a couple of sloppy things needing correction. All possible preventative maintenance was done. All filter/bias/bypass electrolytics were already re-capped - except for one which was replaced with an upgraded voltage and temperature rated CE brand electrolytic. New 2 Watt Reduced Mass Metal Film/5 Watt Cement power dropping resistors were installed for better reliability and lower noise floor. The cathode resistors for V3 and V6 were replaced with 3 Watt Cement type units due to heat damage. All plate resistors were replaced with 2 Watt Reduced Mass Metal Film type units for preventative maintenance and reliability. All screen resistors were replaced with 3 Watt Cement 470 ohm type units for same reasoning.

The original tubes did not test good and were all replaced: V1/V2 = EHX 12AX7, V3/V6 = EHX12AT7, V4 /V5 = JJ 12AX7S, V7-V10 = JJ 6L6GC Matched Quad. These tubes were picked for best tone, and reliability. The 6L6GC's Fixed Bias was set to %55 Class AB Plate Dissipation with a B+ of 412VDC. A new 3 prong AC cord was installed due to the original being cheap and installed wrong. The Death Capacitor was deleted from circuit for safety reasons, rendering the Ground Switch deactivated. The broken SPST Power Switch was replaced with a replica made by Carling. The pots were sprayed out and the amp was cleaned inside and out. Amp now functions well.