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In Reply to: RE: CCS posted by PeterI on May 14, 2015 at 08:13:21
It takes roughly 30 V. to operate a CCS. Additional volts are needed to "track" the I/P signal. Now, consider the potential at which the LTP cathodes "sit", in both Poinz's "Musical Machine" and a Mullard circuit.In the "Musical Machine", the cathodes "sit" a few volts above ground. The negative rail is needed in order for things to work. The grids "sit" at 0 VDC.
OTOH, in a Mullard circuit, the cathodes "sit" a few volts above where the voltage amplifier's plate "sits". Remember, the grids of the LTP's triodes "sit" at the same potential as the voltage amplifier plate they are DC coupled to.
BTW, before Poinz went to the CCS tail load, he too used a resistor. The negative rail was also necessary in that situation.
Eli D.
Edits: 05/14/15Follow Ups:
This number is very dependent on the actual CCS in question. I could think of some that would operate with much less (LM334) or potentially much more (pentode CCS).
The battery biased, depletion-mode MOSFET CCS operating envelope is dependent on how many batteries you use. With 3x 3.3v LI button cells, 15V is about the minimum it should ever see under maximum signal condition.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
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