Those Radio Shack Mini Amps ...

[Kolner]

That's what I ran into as well. All you have to do is disconnect everything from the loudness tap and you're all set.

If you've not already done so, replace all the 1M resistors in the amp. When the amp was new they were known for failure. Any that have lasted this long are probably not at the correct value.

Thanks for the tip! I will have a look.

 

[inperson]

I can't turn my SA-10 up past the 9 o'clock position without getting distortion, even with efficient speakers. Does that indicate a need to change some caps?

 

[Blast]

I can't turn my SA-10 up past the 9 o'clock position without getting distortion, even with efficient speakers. Does that indicate a need to change some caps?

About the 9:00 position on my SA-100B has been my experience, as well. ~1.5w/ch RMS @ 1kHz (by my tests) goes by real fast!

The age of the caps, particularly the electrolytic ones, indicates the need to replace them. If they are still original, and you wish to operate the instrument, then it would be my recommendation to replace them as I did on my SA-100B:

 

[inperson]

About the 9:00 position on my SA-100B has been my experience, as well. ~1.5w/ch RMS @ 1kHz (by my tests) goes by real fast!

The age of the caps, particularly the electrolytic ones, indicates the need to replace them. If they are still original, and you wish to operate the instrument, then it would be my recommendation to replace them as I did on my SA-100B:

View attachment 3492373

I just got a SA-102 Realistic amp and I can turn it up to 12 o'clock with my Minimus 7's for rock and even up to 1 o'clock + for jazz and such. It's a pretty good amp.

 

[atmasphere]

I can't turn my SA-10 up past the 9 o'clock position without getting distortion, even with efficient speakers. Does that indicate a need to change some caps?

If you are intent on using one of these amps, replacing the filter caps is always the first place to start.

If an output transistor has failed the amp won't make much volume before breaking up.

 

[hornbostel]

Optimus SA 155 has been on my bench for years. 1.8 watts, serviceable phono preamp, what’s not to love.
Here she is helping me with open heart surgery on a pair of first gen KLH 6s. Had to check playback of all frequencies before we sealed them back up. Everyone should have one of these little amps!

 

[bolero]

I have a Radio Shack branded SA 155 I want to turn into a preamp

There's some good circuit upgrade notes in this thread too, thanks @atmasphere !!

And maybe use it's 1.8 ? watt output section to drive my hard-to-drive vintage AKG 240's too. I think I can shoehorn an XLR jack in at the rear, by the power transformer

I was wondering why there wasn't a fuse in the unit, apparently it's inside the PT

 

[hornbostel]

One last glamour shot from me of the SA 155. Putting a refurbished Radio Shack Lab. 440 through sea trials. SA 155 driving a pair of Boston Acoustics A40s. White marks on the amp produced an average output of 80 dB. This is where typically test my refurbished loudspeakers, etc with this amp. Sounded fantastic through the SA 155 phono amp.
Huey Lewis and the News Heart and Soul on the vinyl.

 

[topgun]

I’ve had one of those little radio shack mini amplifiers for several years now. I keep it on my bench and mainly use it for testing purposes, and especially for when I’m replacing foam surrounds on speakers. Instantly centers the driver eliminating the need for shims.

 

[Lavane]

I’ve had one of those little radio shack mini amplifiers for several years now. I keep it on my bench and mainly use it for testing purposes, and especially for when I’m replacing foam surrounds on speakers. Instantly centers the driver eliminating the need for shims.

I've had two of them over the years. The black faced version from the mid 70's, and a later silver one. They do make for nice test amps at the bench due to there size. The last one I gave and shipped to another AK'r who had one that died. He also had the little matching tuner. He and his wife really liked the little system. I had started switching to tube based equipment by then, so didn't need it anymore and was happy to send mine along to someone who appreciated these little amps.