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Old 6th Sep 2010, 11:27 am   #21
G8HQP Dave
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Default Re: Bush AC31 Shortwave performance

Was the 22K an early repair - perhaps before leaving the factory? When it was 22K the set might have just worked, or maybe only checked on MW/LW. Someone was short of stock of the correct high wattage 10K, so put in what he had?
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Old 6th Sep 2010, 10:18 pm   #22
AlanC
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Default Re: Bush AC31 Shortwave performance

It's an interesting point. There has in the past, in other theads on this forum, been some dispute over the data given in the Trader sheets. Having said that, I'm inclined to think that with short superhets, each component value will have been optimised to extract every last dB of gain, in order to make the most of the two active stages in the RF/IF side. This would be a compelling reason why 10K is actually correct. Perhaps we'll never know why I had 22K in mine. I'd be interested to know what resistor is in the R5 position in Howards set though... next time you're inside it!!

Thanks for your help, Dave. Much appreciated.
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Old 6th Sep 2010, 10:42 pm   #23
G8HQP Dave
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Default Re: Bush AC31 Shortwave performance

10K sounds more plausible than 22K. The main function of this resistor is to stop the oscillator triode from overheating if it is not oscillating, as then it may have no negative grid bias. On the other hand, it should not drop too much HT during normal operation. FWIW it is 10K (R6) in the Pye P45 too.

I'm glad it is all sorted now.
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Old 6th Sep 2010, 10:49 pm   #24
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Default Re: Bush AC31 Shortwave performance

I'd be surprised to see a big body/spot/tip resistor in this position in an early 50s set, so like Dave I suspect it may have been a 'repair' at some stage. By the 60s these radios had little value and often received dubious repairs from tinkerers.
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Old 6th Sep 2010, 11:17 pm   #25
Leon Crampin
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Default Re: Bush AC31 Shortwave performance

The 10k Ohm smoothing resistor in a DAC90A is a "body, tip, spot" job. I think this type of identification survived for longer in the high wattage carbon comp types.

Leon.
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Old 7th Sep 2010, 11:25 pm   #26
howard
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Default Re: Bush AC31 Shortwave performance

Quote:
Originally Posted by AlanC View Post
.......... I'd be interested to know what resistor is in the R5 position in Howards set though... next time you're inside it!!
........ Dave..........
Hello Alan,

Resistor R5 (as in Trader sheet 1066) in my AC31 measured 31k ohms. According to the Bush service manual this resistor should be 10k ohms or in later sets 22k ohms. Mine is a later model as it has a tone control on the back so I've just replaced it with a better 22k ohm resistor of the same long carbon type. It made no noticeable difference to the performance of the set.

Howard
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Old 10th Sep 2010, 9:32 pm   #27
Phil G4SPZ
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Default Re: Bush AC31 Shortwave performance

For what it's worth, I have a 1948 Bush AC91 which is the most sensitive and stable receiver on short waves that I have ever restored.
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