19-08-2018, 09:45 PM
If it's a voltage-dependant resistor, it's possible that it's being used to hold the 1.5V bias point at a more consistent voltage as the battery wears down.
I also wonder if it's a thermistor? Perhaps to hold the bias constant in the face of ambient temperature changes? Probably less likely...
It reminds me of the funny little voltage regulator in some Tandberg sets that is usually playing up by this time. Those are 2 terminal shunt regulators, and can be replaced by Zeners or a string of normal diodes. Not the same as this, but reminiscent nonetheless...
Anyway, here's what I'd be tempted to do:
Temporarily connect up a variable resistance - an old pot will do if you don't have a decade box. Adjust it until there is 1.5V at the point indicated. Measure the value of resistance needed, and substitute the nearest preferred value resistor. OK, it's not ideal, but until more data about this mystery component comes to light, it'll get the set working, hopefully.
I also wonder if it's a thermistor? Perhaps to hold the bias constant in the face of ambient temperature changes? Probably less likely...
It reminds me of the funny little voltage regulator in some Tandberg sets that is usually playing up by this time. Those are 2 terminal shunt regulators, and can be replaced by Zeners or a string of normal diodes. Not the same as this, but reminiscent nonetheless...
Anyway, here's what I'd be tempted to do:
Temporarily connect up a variable resistance - an old pot will do if you don't have a decade box. Adjust it until there is 1.5V at the point indicated. Measure the value of resistance needed, and substitute the nearest preferred value resistor. OK, it's not ideal, but until more data about this mystery component comes to light, it'll get the set working, hopefully.
