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Vespasian 20th November 2006 02:21 AM

Stromberg Carlson ASR433 Question
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

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

HollowState 20th November 2006 03:37 AM

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.


Vespasian 20th November 2006 04:15 AM

:checked: Thanks Victor ;)

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