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 Astor GPM Radio
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 Return to top of page · Post #: 1 · Written at 8:44:27 AM on 3 January 2022.
Bolster's Gravatar
 Location: Lawson, NSW
 Member since 10 August 2017
 Member #: 2149
 Postcount: 14

Hi All,

I am in need of some assistance with an Astor radio, model GPM, that I am attempting to repair for a friend.

Chassis is in very original condition. Case is in very good condition also.

Problems I have uncovered to date:
1) Audio output transformer primary is open circuit
3) Oscillator coil is also open circuit.
3) Coupling cap to audio output valve was leaky
4) 270K resistor to plate of 6BD7 was very high in value
5) Decoupling cap from plate of 6M5 to ground was shorted
6) Another leaky cap connected from oscillator coil to mixer valve. The oscillator coil had 50v DC cross it & I feel this is what has contributed to it going open .

I temporarily tacked in another audio output transformer & replaced the other components & was able to restore some life to the chassis.

Does anyone have a junked chassis for this model radio amongst their stash that they would be willing to part with? Or possibly have a good output transformer & an oscillator coil? Happy to pay.

My friend has some sentimental attachment to the radio , so I would like to get going if possible. Or is it too far gone?

Any help would be greatly appreciated


 
 Return to top of page · Post #: 2 · Written at 10:24:21 AM on 3 January 2022.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 2149

Jaycar 100 volt line transformer will sub as a output transformer at $11.00 each pretty cheap.


 
 Return to top of page · Post #: 3 · Written at 11:33:04 AM on 3 January 2022.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5239

Which winding of the Oscillator coil is open? Often you will get breaks at the terminals when changing parts. That can often be sorted.

If its the non resonant tickler coil, a few turns of winding wire over the old will sort it. If the new coil is connected up in reverse it will not oscillate, so you try reversing the wires.


 
 Return to top of page · Post #: 4 · Written at 2:23:09 PM on 3 January 2022.
Robbbert's avatar
 Location: Hill Top, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 2011

While you're working on the radio, you should replace every wax capacitor - especially if there's one between the 6BD7 anode and the 6M5 grid.


 
 Return to top of page · Post #: 5 · Written at 11:32:26 AM on 4 January 2022.
Bolster's Gravatar
 Location: Lawson, NSW
 Member since 10 August 2017
 Member #: 2149
 Postcount: 14

Thanks Tallar Carl for the tip regarding the substitute transformer.

Marcc, I'll recheck the oscillator coil & have a closer look at the terminals.

Robbbert, I have already temporarily replaced the cap between the 6BD7 plate and the 6M5 grid (along with a few others) during the fault finding process, as the bias to the 6M5 was way off. Once radio is working again, all the wax caps will be replaced.


 
 Return to top of page · Post #: 6 · Written at 4:02:45 PM on 4 January 2022.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 5239

There is debate re introducing faults changing things; But! In my decades of fixing, often commercially, yes! There are things to do before applying power; however, I consider it a waste of time and an exercise in futility, fault finding a radio containing aged electrolytic caps (anywhere) and waxed paper caps, which if not shorted , will by now electrically leak like sieves.

Always check resistors as you go. Mica caps often found across coils in the RF should not be touched.


 
 Return to top of page · Post #: 7 · Written at 8:13:19 AM on 6 January 2022.
Wa2ise's avatar
 Location: Oradell, US
 Member since 2 April 2010
 Member #: 643
 Postcount: 830

QUOTE: cap from plate of 6M5 to ground was shorted

surely caused
QUOTE: Audio output transformer primary is open circuit


Be sure to recap all the other wax caps!


 
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