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Cathode Windings

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Hi ,

I salvaged a pair Fisher output transformers with tertiary windings to be used as cathode windings .The outputs are 4300k CT primary winding , 280 ohm CT tertiary primary winding and 16 , 8 ohm secondary at about 30 watts and is slightly larger than Dynaco ST 70 transfomers .I am wanting to use these with PP 5881 or 6CA7 in triode mode using the cathode windings .Will i have to stick with cathode bias or is a seperate bias supply practicle . Would a driver PCB such as a Posiden or Triode electronics MK4 have enough gain to drive the output using the cathode feedback windings .I'm open to driver curciut sugestions the only circuit i have found that use cathode windings like this is the Quad II and the Fisher model 80AZ .
http://www.ampslab.com/vintage_fisher80az.htm

Mark
 
With both plate to screen (Triode Strap) and cathode Schading
in effect simultaneously, your output stage voltage gain may be
very very low. You are going to need a really big drive signal.

Drive of that magnitude might venture into grid conduction.
I would suggest you simulate in LTSpice before committing.
Will providing that current cause the very distortion you wish
all this local feedback to prevent?

Might want to keep your options open for a Pentode or UL
screen strapping. If you are going with strong local feedback
into the cathode...

Remember the work of OHSchade(RCA 1939). This sort of
feedback makes almost the same curves as Triode anyway.
 
kenpeter said:
With both plate to screen (Triode Strap) and cathode Schading
in effect simultaneously, your output stage voltage gain may be
very very low. You are going to need a really big drive signal.

Drive of that magnitude might venture into grid conduction.
I would suggest you simulate in LTSpice before committing.
Will providing that current cause the very distortion you wish
all this local feedback to prevent?

Might want to keep your options open for a Pentode or UL
screen strapping. If you are going with strong local feedback
into the cathode...

Remember the work of OHSchade(RCA 1939). This sort of
feedback makes almost the same curves as Triode anyway.


hey-Hey!!!,
The grid-cathode drive requirements are the same in any of these topologies, including the unity-coupled McIntosh. The large voltage is seen grid-ground, but that becomes a driver capability issue, not a power final grid current problem.
cheers,
Douglas
 
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