Cascoding tubes

[Bandersnatch]

Originally Posted by Tony

may i know your operating point for the 6H30?

hey Tony,
It has the MOSFET gate at ~110V and is passing 15 mA at idle per triode. It is arranged as a LTP over a CCS, and I don't worry about the value of the bias; that takes care of itself. B+ is over 550V, and the MOSFET drain is ~330V( all from ground ). It can take a 6H6pi with only a slight reduction in gain and these are generally better matched section-section( not to mention being much cheaper ).
cheers,
Douglas

[dhsettim]

Originally Posted by Gary P

A variation I've tried with pentodes and will be trying with cascoded triodes in the near future is to put a very good CCS on top of the upper cascode element and connect the plate resistor to ground. The CCS provides all the current for both the cascoded triodes (or pentode) and the plate resistor. This shortens the signal path to include only the cathode resistor, the amplifying element and the plate load. The CCS provides very good power supply isolation.

For an example look at the "driver experiments" section on my web page.

Gary,
after reading your driver experiments page I had the same idea except to use a hybrid cascode as per AW. Even to using 2 or 3 MAT02 on the bottom for huge TransC. Then with a mu output impedance of circa 500R it is almost ideal to drive a 600R LCR riaa.
Cool
tim
PS AW would call this vapourware (I think)