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| Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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26th May 2017, 11:52 pm
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Nonode
Join Date: Aug 2007
Location: Walsall Wood, Aldridge, Walsall, UK.
Posts: 2,874
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"Wheatstone Bridge" Hum Cancellation!
Hi!
I think this technique originiated from Australia as an alternative method of residul-hum cancellation in inexpensive receivers to avoid the use of expensive chokes, high-wattage-resistors, and the need to have the h.t. output from the rectifier no more than the absolute minimum needed for the output valve! It's based on "Wheatstone Bridge" techniques, and has the advantage of not needing an O/P transformer with a tap on it! Altho' shown for an a.c. only receiver, it can be used for an a.c./d.c. type power pack, but care needs to be taken not to accidentally interpose the heater-chain current in the -h.t. lead bias resistor - this is ensured by lifting the bottom-end of the heater-chain from chassis, directly returning it to mains N via the on/off switch neutral-pole, then connecting the bias resistor from there to chassis. I attach the paper the idea came from! Chris Williams
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It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed! |
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