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Old 29th Nov 2018, 2:25 pm   #1
cernem1alt
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Default Bush DAC90A blocking capacitor location?

Got a crackly volume switch issue and the volume is loud I have been told to check the blocking capacitor, could someone point me into where this is please?
I have changed all the caps and resistors and a new audio transformer and have brought a dead set back to life just need to sort out this issue and I am done. Thanks Mike
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Old 29th Nov 2018, 2:44 pm   #2
kalee20
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Default Re: Bush DAC90A blocking capacitor location?

A noisy volume control can be caused by excessive DC on the volume control, caused by a leaky coupling capacitor. But not in the DAC90a, where the design does inherently put DC on the control, albeit just a few volts, and nothing to do with a bad capacitor.

It's a new control you'll need.
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Old 29th Nov 2018, 2:54 pm   #3
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Default Re: Bush DAC90A blocking capacitor location?

Or take the control apart and carefully clean the track and metal centre contact. Dont rub the carbon track hard or you may wipe away the carbon.
Then put a thin smear of grease on the track and the centre metal contact where the centre wiper makes contact.
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Old 29th Nov 2018, 5:08 pm   #4
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Default Re: Bush DAC90A blocking capacitor location?

Found a replacement from Bowood electronics so will give that a go
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Old 29th Nov 2018, 6:37 pm   #5
Graham G3ZVT
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Default Re: Bush DAC90A blocking capacitor location?

Changing all the capacitors and resistors seems unnecessarily heroic. Perhaps you meant a limited number of components recommended for replacement.

Any such list should have included the output grid coupling capacitor 0.01uf circled below.
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Old 29th Nov 2018, 7:14 pm   #6
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Default Re: Bush DAC90A blocking capacitor location?

Generally a waste of time changing all the resistors. Even if the originals are slightly off tolerance, changing them will make little or no difference. Valve radios are very forgiving (with a few exceptions) with resistor values.
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