Quote:
Originally Posted by Uncle Bulgaria
This morning's reading has been on BJT switches, though the accepted circuits I've found have the emitter grounded.
I'm guessing that the biasing on T10 is meaning the switch is not turning off properly. The current on the base means it is not biased into cut-off when the switch is open.
Does this mean the S1002 acts to allow current to flow between the 9.5V rail on the collector, through the 2.2K R79 which should turn the switch on?
In which case, should I be increasing the values of R81 and R79 to decrease base current, even though the Zener diode is holding the base to 5.6V?
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Battery operation....Bias is supplied from the battery to turn on T10 via switch contacts 14&15 on the 12/24 volt input socket assembly>>>the on/off switch contacts>>>K4 switch contacts (on record) or contacts 37&38 of S1 (on playback)>>>contacts 5&6 of S1002>>>R79.
Mains operation....Bias is supplied from the regulator T606>>>contacts IV&VI (mains unit aka Z131 inserted)>>>the on/off switch contacts>>>K4 switch contacts (on record) or contacts 37&38 of S1 (on playback)>>>contacts 5&6 of S1002>>>R79.....
….Also from the regulator T606>>>R81>>>R79 when contacts 5&6 of S1002 break....So far as I can make out.
I wouldn't alter those resistors.
EDIT: Post crossed.
Lawrence.