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Bush PB61 problems

 
Radio
Last Post by Anonymous 14 years ago
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 Brian Cuff
(@briancuff)
Posts: 2059
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Topic starter
 

Hi all - I need some help.
I'm not really a radio man but a friend asked me to get his PB61 going for sentimental reasons, it was his parents' radio and it was on all the time during his childhood.
The first thing I found was a short on one of the HT windings but I was able to find a suitable transformer at Wooton Bassett a few of weeks ago. That's in now with the electrolytics and waxies changed and surprisingly, over half the resistors which had gone more than 20% high. There was also a lot of rubber insulated wire which had to be replaced.
It works now but the gain is very low, bringing in a couple of commercial stations and little else. The strange thing is that connecting an aerial makes very little difference to the reception. This pointed me to the aerial section of the FC but all seems well here and the voltages are within a gnat's whisker of the book values. It has air-cored coils so tracking is pretty well up to the design as there are only caps to vary.
Any suggestions?

 
Posted : 25/07/2011 9:16 pm
 Brian Cuff
(@briancuff)
Posts: 2059
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There's no cap for LW & MW, Trevor, as the aerial goes straight to primary windings on the mixer input coils. The signal increases if I touch the secondaries but the mixer coils are aligned properly.
I have found that the volume control was introducing loss even at fully C/W so I've changed that. It's a little better now but still pretty insensitive although it pulls in signals with no aerial connected - I don't understand it   :x  😡

 
Posted : 26/07/2011 11:36 pm
 Spot-Wobble
(@spot-wobble)
Posts: 732
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Have you checked the alignment?

Andy

 
Posted : 28/07/2011 1:16 pm
 Brian Cuff
(@briancuff)
Posts: 2059
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Topic starter
 

Several Times Andy. One of the problems is that the coils are air cored so have no adjustment so the sensitivity is better at the HF ends of the bands but falls off at the other end. The set also has a bad case of Modulation Hum so I have added the normal caps (X2). It is very strange as the amount of hum changes with my position in the workshop!!!

 
Posted : 28/07/2011 2:01 pm
 sideband
(@sideband)
Posts: 4268
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I've had mixed results with air-cored coils. I've got a Cossor 500 which is decidedly deaf unless you stick a whacking great aerial on it. However I've found that it has improved considerably during the hot waether and I suspect that the aerial coils had absorbed moisture which has now dried out. Worth considering. Is there a 'bottom-end' coupling capacitor? This was a very common arrangement at one time. If this capacitor goes O/C or lossy, it kills the aerial circuit.

SB

 
Posted : 28/07/2011 2:28 pm
 Anonymous
(@anonymous)
Posts: 16844
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i wounder if you have checked the agc circuit r1,r7,and c17 (trader 1365)
rob t

 
Posted : 08/08/2011 8:23 pm
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