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CCS Mu output question

Posted by DanK tubes (A) on March 5, 2017 at 15:17:09

Hi all,
I have a question about the Mu follower output of a cascade CCS.

The Mu output should be able to drive a low impedance. What if you were to take a low current driver tube, say a 12ax7, and load it with a cascade CCS. The 12ax7 should not be able to drive the miller capacitance of a big triode, like a 300b. But, can the Mu-output, on top of a 12ax7, drive 300b?

I've copied some notes from Gary Pimm below. (Thanks Gary!).

Thanks,
Dan


"Using a CCS as a combined CCS and mu follower

When an n-channel mosfet is used for a CCS we have an opportunity to get a second function almost for "free". The output signal can be taken from the source of the lower mosfet instead of the plate of the triode. Refer to the schematic above to see the circuit detail of where the signal is taken from.

When driving output triodes or interconnect cables that are high capacitance loads, this arrangement works very well. The driving triode is isolated from the load capacitance to maintain constant current operation at high frequencies and the next stage is driven from low source impedance."

--Gary Pimm
pimmlabs.com

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