Update - 11Aug15:
I didn't realize how long it's been since I put my hands on this amp. Life is just too complicated. I have a couple days off before working an 8-day stretch of long hours. It's a rotating schedule at the plant, so I know when it's coming.
I replaced the second canned capacitor in the power amp, and now that chassis is very quiet. It houses the Power Amp and Reverb. The Pre-amp is connected by means of a shielded cable, RCA plug on the end. I fabbed up a small metal project box with two closed-circuit phone jacks, and two RCA phono jacks. This is for an Effects Loop to mount in a rectangular hole on top of the cabinet. Before, there was a plate with two open-circuit phone jacks, paralleled with the 'Stereo' input. I believe that the onboard, four-pin stereo jack is for an accordion, as Sano catered to the accordion market. The amp is overall very quiet, even though the Pre-amp does not have a chassis around it. It's just mounted to the Faceplate.
Again the Reverb is plenty strong and the Tremolo is weak. I can see that a drawing is in order, at some point, to properly troubleshoot by. There is a Guitar input, Instrument input, and another unlabeled input. I'll inspect closer when I'm making a drawing. It's a lower gain, and is affected by the Master Volume, only. The Reverb, Guitar, and Instrument inputs have their on Volume/Gain pots. I'm thinking this one ties in somewhere downstream of the Guitar and Instrument.
What a really nice sounding amp this has turned out to be. With no history, a very trashy appearance (dirty inside and out), and many input modifications, it has come back to life in a fine way. I believe that I have it very stock, with the exception of my FX Loop. No wiring mods, on my part.
Next fix will be to straighten out the power switch, as it has no affect. Power is always on, if the power cord is connected. I use the switch on my limiter box, when I'm working on it. My limiter has a lamp socket, fuse holder with 3-amp fuse, and a typical wall switch (though I put one in rated for 20 amps). When I want full line voltage/current, I screw in a plug fuse replacement circuit breaker, in place of a lamp. The receptacle is protected by the small fuse, at all times. I also have a ground binding post (green), so that I can run an alligator jumper to a chassis that may not have a grounded cord.
Anyway, I'll snap a couple of pictures when the rest of the fixes are done. Particularly, the FX box and the front with the Sano badge rotated to it's correct position. More to come. Have a good one.
Jack