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UL to triode mode conversion on cathode bias amp-different cathode resistors needed?

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bigwill

Member
2004-12-25 8:36 pm
UK
Quick question - I have a Radford STA15 and I'd like to try it in triode mode. It currently has KT77s in it and biases up fine. Am I right in guessing ultra linear output stages essentially act as triodes at around DC? (The screen goes to B+ through the OPT through a resistance much like connecting the plate and screen together via a resistor)

Will disconnecting the ultra linear tap force me to change the cathode resistance to retain the correct bias?

Amp schematic

http://www.freeinfosociety.com/electronics/schematics/audio/pictures/radfordsta15.gif
 

tubewade

Member
2007-06-03 8:54 pm
bigwill,

The schematic link did not work for me.

You should not have to change the cathode resistance(s) to switch from UL to triode mode. The voltage at the screens should not change from one configuration to the other and the quiescent current through the valve should be the same either way.

Best regards.
 
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