I have two suspicious transistors. What's marked on them is as follows:

1. 693GS (it has a round head on it)
2. MPS 6518 or 651B (There is a Motorola M just before the MPS)

These were taking from the preamp board of my TEAC reel to reel tape recorder.

I am getting a static low volume roar out of the left channel.

Thanks for your help identifying these!

The 693GS can probably be replaced with an NTE 123AP. The MPS6518 can be subbed with aN NTE 159.

96% probablility the Motorola was a service substitute. I don't recall ever seeing a US semiconductor brand in Japanese electronics. The originals were most likely Toshiba.

Thanks so much! On order!

Always use 2SC2240 for NPN replacements and 2SA992 for PNP replacements.

The NTE123A is suitable for troubleshooting applications, but I would NEVER install it in a low-noise circuit.

* * * * *

Also, most technicians would squirt some freeze-mist on a transistor suspected of being noisy. If this reduces the noise audibly, it corroborates your suspicion that the device is defective. Finally, you can measure transistor leakage with an ordinary ohmmeter.

Fred
owner
Classic Audio Repair

A bit off topic for this thread, but related, I have a question.
Is there any similarity between the A-1250 and the A-1200U?
Wondering.
Mark D.

The A-1250 is a much newer machine than the A-1200U. The "U" stands for "Universal" export model which works on many line voltages and 50/60 Hz. The A 1200 series is from the late 1960's.

Jim L.

Never knew what the U stands for, but my Teac is an A-1200U, according to the model number on it. But it is only 120VAC. (117) There is no provision (that I know of) for it to operate on different voltage or frequencies.
Maybe there are taps inside on a transformer. I wouldn't know about that.
I didn't know about the years of difference between the A1200 and the A1250, thought I'd ask, on the chance that there might be some similarities.
Thanks
Mark D.