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Old 23rd Feb 2016, 11:36 am   #57
ms660
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Join Date: Apr 2011
Location: Cornwall, UK.
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Default Re: HMV 653 Broadcaster all wave.

The HT reservoir capacitor is C25 on both schematics it's -ve connection is referenced to the rectifier via the HT transformer center tap as it should be.

The receivers current draw sets the receivers bias line voltage which is developed across the 270 ohm resistor (R21 trader, R17 service mans) the current draw for practical purposes will be not far off constant in this type of receiver, hence the bias line voltage will be more or less constant. The value of the resistor that develops the bias line needs to be small compared to the value of the HT filter resistors which it is.

If there was no reservoir capacitor the rectifier would be looking at a choke input filter and the HT voltage would be considerably less than what is quoted.

Lawrence.
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