Fender SF Dual Showman Reverb MV wiring

[nevetslab]

I have a Fender SF Dual Showman Reverb amp on the bench, now past the re-cap of the 43 year old electrolytics and coupling caps, and found myself wondering about the Shield / Ground connection of the bottom of the Master Volume pot. It's sitting at the junction of the 820 ohm feedback from the output of the amp, bottom of the LTPI Cathode network, 100 ohms above ground. While I only have SF Twin Reverb schematics to go by on this, it looks to be the same thing in this regard. I see that connection clearly shown that way on the schematic. Is that correct, or is this a mistake made decades ago and, it being just 100 ohms above ground and part of that LT pair circuit, it doesn't matter. Why wouldn't the bottom of the master volume pot connect to ground instead of here? I haven't moved it....just wondering? I've pointed to the circuit connections in question with a green probe.



twin_reverb_sf_100_schem.pdf

[Helmholtz]

My '74 Dual Showman Reverb is the same. I never cared about the MV wiring, because I don't consider it a useful feature in this amp. It works though.

Did you have a reason to replace the blue "molded" capacitors? They are good quality Mylar/polyester types, that don't tend to show deterioration. I prefer them to orange drops.

[nevetslab]

My '74 Dual Showman Reverb is the same. I never cared about the MV wiring, because I don't consider it a useful feature in this amp. It works though.

Did you have a reason to replace the blue "molded" capacitors? They are good quality Mylar/polyester types, that don't tend to show deterioration. I prefer them to orange drops.

The replacement of the blue molded mylar caps was done just as a matter of course, changing to the metallized polypropylene dielectric.

[Randall]

It's funny how things come around. In the eighties and maybe nineties everyone wanted to change those blue Mallorys out for orange drops. Now everyone wants the original blue Mallorys again., and you see the blue Mallorys for sale on ebay. Personally, if the blue Mallorys are not leaking, I consider it a blessing and leave them in. As a matter of fact, if I open a vintage Fender while the customer is here, I point this out as a good thing. I mean, those amps sounded GOOD with those caps, so why are we changing them if they are not bad?

[Helmholtz]

I never found a leaky blue "molded" Mallory (measured many of them). Quite the contrary with yellow and red Astrons, which were a different technology.
FWIW, Mylar/polyester caps can stand higher temperatures than polypropylene ones, which may make a difference when soldering with short leads.