Thermal runaway. Remember that well. R&TV Supplies in Acton did a transistor
radio kit called the elegant 7, yes a whole 7 transistors.
Trouble was almost evey component in it was a substtute for the intended
one in the original design. the single ended push/pull ciruit specified
Get 114 transistors, but the supplied ones on f dubious manufactur were
labelled S1. The radio worked for about ten mins, then started to distort
and stop. The S1 transistors got red hot. Leaving it off for a few minutes
repeated the effect. Probably not have got away with this on a mains psu.
After some poking at the company they sent us the right ones and then it
worked and still did the last time I tried it.
Goes to show tht thermal runaway can be very interesting.
No heat sink in this radio as it had a 35 ohm speaker and only gave out 500
Mw supposedly.
Brian

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The Sofa of Brian Gaff...

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"Don Pearce" wrote in message
...
On Fri, 10 Jun 2016 14:50:08 +0100, "Dave Plowman (News)"
wrote:

In article ,
Phil Allison wrote:
does anyone still use germanium transistor amps - anywhere ?

Just by coincidence used one yesterday. A couple of ancient Henry's radio
kits which I put in a case with a rudimentary pre-amp many years ago. Only
10 watts per channel. The sort of thing you could leave lying around and
wouldn't get nicked. ;-)

Never did any measurements on it - but it sounded OK for the things it got
used for.

I seem to remember you had to be conservative with Germanium power
amps. Thermal runaway was always lurking just around the corner.

d

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