Hello all,
I have a 1970's Radio Shack phono here that I've
completed restoring the BSR changer.

With some old Panasonic speakers, it sounds very good,
except the left channel is putting out a shushing or surf-like sound.
Sound is not really loud, but I'm wondering if it is indicating a coming
failure.
I know very little about SS amps, would there be
a logical troubleshooting starting point ?
I have a good DMM to use.
Thanks for bearing with me,
Hotwax

Bad transistors

Okay, I figured it was a transistor.

I lucked out and found the schematic on the
bottom of the cabinet. Posting it.

I did some reading on transistors (npn, pnp differences
and how they appear on schematic)

Can someone now direct me on what to do next ?

Remember, this is my first foray into SS amps,
so be kind and detailed, ha !
H

Transistors consist of a emitter, base and collector. The legend is up at the top of the schematic. Start by taking voltage measurements with a vtvm. Unfortunately it needs to a sensitive meter such as this. The other option is that most modern meters have transistor checkers on them. The bad news is that you have to know the exact transistor number to find the replacement.

It was made by Arvin; they also made similar units for Sears.

The preamp stage is an FET (field effect transistor). If you have an oscilloscope or signal tracer, the noisy component should be easy to find. Remember, you have one working channel to compare the noisy one to. As old as that unit is, it is possible to have a leaky electrolytic capacitor or noisy resistor as well.

In the shop, we would hit all of the transistors and other components with cooling spray, one at a time. That would usually reveal the culprit.

Id'n that sound to a transistor is highly probable. But I would replace all the electrolytics before probing the transistors and possibly blowing one.

Bill J.