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Old 9th Feb 2023, 11:40 am   #10
stuarth
Heptode
 
Join Date: Feb 2010
Location: Heysham, Lancashire, UK.
Posts: 665
Default Re: Help Needed - Armstrong 626 Tuner Amplifier

To avoid the destruction of the new transistors because there were other faults, I used to wire a 270R 3W wirewound resistor in series with the DC supply to the power amp. If all was well, the amplifier worked normally at low volume with very little voltage drop across the 270R. If there was a remaining fault and the amp drew excessive current, the resistor would get very hot very quickly. With separate DC fuses for each power output stage, it is very easy to remove the fuse and tag the resistor across the fuseholder.

This trick is usually quick and easy to apply. I used radial leaded resistors with mini crock clips directly on the resistor leads, it was self supporting in mid air. Using these resistors, I never blew the replacement transistors, and I always noticed the hot resistor before it came to harm (dissipation would be over 3W on most amps).

Stuart
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