07-10-2021, 10:09 AM
(This post was last modified: 07-10-2021, 10:15 AM by ppppenguin.)
I only have the Trader circuit to hand and it's for the TR82B, not C but the designs are fairly similar.
The quoted voltages for TR1 must be an error in the service data. The base voltage must always be greater thant he emitter voltage for a transistor to conduct at all. I would expect to see about 0.2V to 0.3V for a germanium transistor such as those in this radio. Remember also that all voltages in this set are -ve wrt the chassis, even though they are expressed as +ve numbers.
I assume you understand that all voltages are measured wrt chassis or battery +ve.
Small variations from the "official" voltages are not important but 2 things stand out
TR4 OC71 0.12V (1.0V) 1.3V (1.1V) 1.7V (1.5V)
-------------------------------------------------------------------------
TR5 OC81D 1.7V (1.3V) 1.5V (1.5V) 8.8V (8.3V)
Assuming your measurements are correct, TR4 looks faulty. A working germanium transistor simply can't have about 1.2V between base and emiter. Also the readings for TR5 are odd. If the emitter voltage is higher (more -ve) than the base voltage it cannot be conducting at all.
These could be faulty transistors, though the ones used in this set are generally reliable. Or it could be measurement error (easily done even by experienced engineers) or other faulty components.
PS: Useful article about the various radios that Bush put in the this design of cabinet: https://www.aireradio.org/riviste_estere/BVWS/Bush.pdf The TR82B and C are the same internally but it look like there were slightly different types of transistors used even in sets of the same nominal model.
The quoted voltages for TR1 must be an error in the service data. The base voltage must always be greater thant he emitter voltage for a transistor to conduct at all. I would expect to see about 0.2V to 0.3V for a germanium transistor such as those in this radio. Remember also that all voltages in this set are -ve wrt the chassis, even though they are expressed as +ve numbers.
I assume you understand that all voltages are measured wrt chassis or battery +ve.
Small variations from the "official" voltages are not important but 2 things stand out
TR4 OC71 0.12V (1.0V) 1.3V (1.1V) 1.7V (1.5V)
-------------------------------------------------------------------------
TR5 OC81D 1.7V (1.3V) 1.5V (1.5V) 8.8V (8.3V)
Assuming your measurements are correct, TR4 looks faulty. A working germanium transistor simply can't have about 1.2V between base and emiter. Also the readings for TR5 are odd. If the emitter voltage is higher (more -ve) than the base voltage it cannot be conducting at all.
These could be faulty transistors, though the ones used in this set are generally reliable. Or it could be measurement error (easily done even by experienced engineers) or other faulty components.
PS: Useful article about the various radios that Bush put in the this design of cabinet: https://www.aireradio.org/riviste_estere/BVWS/Bush.pdf The TR82B and C are the same internally but it look like there were slightly different types of transistors used even in sets of the same nominal model.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
