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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Stromberg Carlson ASR433 Question

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Vespasian

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Joined 2006
#1
Hoping someone could take a minute and help me understand this Hum Balance circuit design. A 6.3vac secondary feeds the el84 heaters but also a 100 ohm pot, which feeds the cathodes.
I apologize if this is really basic stuff but everyone here has been very good to me so I'm not too shy to ask... TIA - Cheers, Ed

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.


Second pic down shows the pot, the 150 ohm resistor and the 25mfd cap to ground; The assembly is a tad messy...

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.
 
#2
Hi Ed,

Try to think of it more as the cathode potential feeding the pot. By applying a small amount of DC to the filament from the cathodes, you bring them to the same level. This is often done in lieu of grounding the pot center arm to balance out hum. This B+ could come from any source by using appropriate voltage divider resistors, but the tubes elevated cathodes simply provides a handy source.

Victor
 
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