Stewart 1400-PA

[agedhorse]

I 've already emailed Stewart and they told me they don't repair this model anymore ...so i guess that answers the question>obsolete/unavailable parts. If they won't repair it....well then.
Which I guess I woulda found out from any svs.tech I would take it to after they opened it . assessed and then charge me for the diagnostic....
Do reputable techs research 1st to see if they can get parts before they put it on the bench?

Some parts are likely unavailable, but many (or most) parts are not a problem. Generally a tech would let you know of this possibility IF they were aware of it, but they wouldn't know that the problem was an unavailable part until it was properly diagnosed.

IIRC, there are some power supply parts that are unobtanium but that's from a recollection.

 

[byacey]

I have some old GK 2000RB amps. I started with one that looked really nice but has been a real lemon. When I bought it, one output section was intermittent and the fan didn't want to come on. The first problem was caused by a flaky fuse. While trouble shooting the fan, I accidentally brushed a component with a test probe and caused a major melt down in the output section. Blown drivers, blown diodes, blown resistors, blown output devices. I did some troubleshooting and then starting researching the needed semiconductors. Turns out the outputs and drivers are obsolete. I found one source, but the minimum purchase was 50 each. This may have been a blessing in disguise since there was so much damage spread throughout the circuit.

This happened to me once, I was using the short ground lead attached to the scope probe, and it came un-clipped from the chassis when I was relocating the probe and fell down onto the PC board; I wound up rebuilding half the amplifier. Now, I always use a separate ground lead from the scope front panel terminal for basic test prodding.

Most times, almost everything is repairable, it's just a matter of time and money determining if it's worthwhile.
Years ago I had an AB 1100A on the bench that the PC board actually had a sizeable hole burnt through the PC board. AB wasn't forthcoming with a replacement PC board, so I designed and etched a suitable board to splice / epoxy into the original board after the burnt section was removed, and repaired the amp as normal. Many other techs would have simply slapped the cover back on and deem it not repairable.

 

[agedhorse]

Back then, the AB-1100A was an expensive, powerful 3 tier class G/H amp worth putting effort into.