"Dave Plowman (News)" wrote in
message ...
Have a home made amp in the workshop which is used a great
deal - I tend
to listen to the radio all the time I'm in there. And of
course doubles as
a test amp for anything needed. My diagrams for it are
dated 1997, and
it's worked just fine since I built it.

Until last Friday. Had to turn the volume well up to hear
anything.

It has balanced inputs, and the unbalanced outputs appear
beside the
workbench as phonos, and are normally jumpered across to
the pre-amp
inputs. The speaker outputs and inputs also appear there.

A quick fiddle showed it was the balanced to unbalanced
side which had
died. Both channels. The PS for these is independant of
the power amp one,
+/- 15v regulated, and its LEDs showed it working.

For some reason shrouded in the mists of time, I'd used
SSM 2017 rather
than the more usual SSM 2143, etc. Perhaps to give a bit
more gain. Or
perhaps just because I had loads.

Both had blown. Replaced and all is now fine.

The pre-amp shares the same PS.

Only odd thing was the severe lightening we had on
Thursday - as
spectacular as I've seen in London. But it was switched
off then, although
still connected to ground (and neutral)

The balanced inputs would still have been connected to my
distribution
system - but everything else on that is fine. And the
cabling for that is
all internal.

Any guesses?




You don't have to have a direct hit for damage - a coronal
discharge (like a thick glow) can also hammer things. Many
times have I been called out to radio sites and found the
equipment intact but power supply series transistors usually
o/c. Switched modes don't like it up 'em either!


--
Woody

harrogate three at ntlworld dot com