08-07-2023, 06:13 PM
Take a look at this post at the Antique Radio Forum:
https://www.antiqueradios.com/forums/vie...=1&t=84205
I have never encountered a SW disabled radio but I have not restored a large number of radios to personally experience this action.
None the less, it is clear that the issue will be related to the RF/oscillator/mixer sections of the radio.
According to the article any number of methods may have been used to disable.
However, it is possible that one or more sections of RF/IF/Oscillator coils could be defective from corrosion or failure from a nearby lightning strike.
Removing a coupling cap associated with shortwave bands could do this or cutting jumpers from RF coils to the band-switch.
Point by point following the schematic, well, that is possible but very time consuming.
I would try to determine if the oscillator is working on each band at each ends of the dial. A "weak" oscillator tube could be a cause as well. A portable SW radio can be used to "sniff" for the oscillator. The radio should pick up the oscillator as a quieting effect that is tunable at the radio in question. I would expect oscillator radiation from a bottoms up chassis to be detectable at least a foot or more from the radio.
If the oscillator is working it could be a defect or a disable in the antenna coils too.
Care must be taken if injecting a signal into the radio as it is possible to accidentally connect to a plate circuit and roast the attenuator on the generator. A more elegant and safe way to get a signal into the radio for testing is to fabricate a five to ten turn coil of 14-16 ga solid insulated (like house wire), make coil about 3/4" dia and create with the wire at least 6" long ends that can be made to a coax to the generator. No need to attach a ground to generator. The coil will show some direction properties so explore how it couples, sort of like feeling for a slot on a blind screw.
Do not forget to modulate the signal from the generator...
Checking all the RF/OSC coils in the radio for continuity is practical, if no resistance is given anything from 5 to 30 ohms is likely good but over 100 ohms would indicate either a miss-measurement or an open coil.
Unless someone has recorded a list of faults for this radio, there are no quick fixes, just systematic troubleshooting and determination...
YMMV
Chas
https://www.antiqueradios.com/forums/vie...=1&t=84205
I have never encountered a SW disabled radio but I have not restored a large number of radios to personally experience this action.
None the less, it is clear that the issue will be related to the RF/oscillator/mixer sections of the radio.
According to the article any number of methods may have been used to disable.
However, it is possible that one or more sections of RF/IF/Oscillator coils could be defective from corrosion or failure from a nearby lightning strike.
Removing a coupling cap associated with shortwave bands could do this or cutting jumpers from RF coils to the band-switch.
Point by point following the schematic, well, that is possible but very time consuming.
I would try to determine if the oscillator is working on each band at each ends of the dial. A "weak" oscillator tube could be a cause as well. A portable SW radio can be used to "sniff" for the oscillator. The radio should pick up the oscillator as a quieting effect that is tunable at the radio in question. I would expect oscillator radiation from a bottoms up chassis to be detectable at least a foot or more from the radio.
If the oscillator is working it could be a defect or a disable in the antenna coils too.
Care must be taken if injecting a signal into the radio as it is possible to accidentally connect to a plate circuit and roast the attenuator on the generator. A more elegant and safe way to get a signal into the radio for testing is to fabricate a five to ten turn coil of 14-16 ga solid insulated (like house wire), make coil about 3/4" dia and create with the wire at least 6" long ends that can be made to a coax to the generator. No need to attach a ground to generator. The coil will show some direction properties so explore how it couples, sort of like feeling for a slot on a blind screw.
Do not forget to modulate the signal from the generator...
Checking all the RF/OSC coils in the radio for continuity is practical, if no resistance is given anything from 5 to 30 ohms is likely good but over 100 ohms would indicate either a miss-measurement or an open coil.
Unless someone has recorded a list of faults for this radio, there are no quick fixes, just systematic troubleshooting and determination...
YMMV
Chas
Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
