Hi!

I think the reason could be the supply voltage. Seems they can
take anything from 27 to 40-odd volts, which might explain
the varied reliability.

Hmm...that is a thought. It might also explain why these little
receivers run so darn hot. Interestingly, mine seems to run hottest
when idle.

I too was surprised at the lack of protection visbile in this amp.
there's only a resistor separating the o/p from the speakers!
ironiocally in this case, the protection seems to kick in far too
early - muting the o/p even when the sound is barely audible.

Be glad it does, but please don't use it with valuable speakers or
depend upon it to work correctly. All too often it...doesn't. The
result is smoke from your speakers.

That is why I was so surprised that the SA-929 receiver I found had an
honest to goodness relay. What motivated Technics to use one there
when they didn't use one in the other models I've seen?

Might this work as a drop in replacement? the output would only
be 15 watts, but better than nothing.....

As they're all pin compatible, I think you can pretty much swap them
at will as long as the voltage ranges are the same for each part. You
probably couldn't get away with a bigger module (it would surely
overtax the power supply) but a smaller one ought to work, especially
if not driven hard or into inefficient speakers. The page that I
linked to suggests that sometimes a larger module was used at reduced
voltage and current levels.

You'd be surprised what "just" fifteen watts worth of output power
will do in terms of volume output.

If you try it, please do post back!

William