6922 as a CCS, a question ?

[Eli Duttman]

FWIW, a pentode makes a better current sink than a triode.

Wiring 1/2 a 6922 as a cathode follower and loading it with a CC 6AU6 should accomplish your near unity gain goal nicely. A stack of 3X red LEDs will take care of 6922 biasing needs. Use a B+ rail of approx 175 V. You will set the 6922 Ib to 3.5 mA. Cap. couple the 6922's cathode to the O/P. Wire a 1 MOhm resistor across the O/P RCA jack's terminals.

Use a 1.2 KOhm cathode resistor on the 6AU6. Connect the "legs" of a 1 MOhm pot. between B+ and ground. Connect the wiper of the pot. to the 6AU6's control grid. Connect the 6AU6's screen grid to its plate via a 1 MOhm resistor. Ground the screen grid via a 100 nF. cap. Starting at the grounded end, adjust the wiper of the 1 MOhm pot. to yield a drop of 4.2 V. across the 1.2 KOhm cathode resistor.

Separate floating supplies for the 6922 and 6AU6 heaters are indicated. DC on the 6922 heater would not hurt.

[Eli Duttman]

Don't forget the Carbon composition stopper resistors (1 KOhm grid and 100 Ohm plate) on the 6922, regardless of the topology you settle on. The 6922 is a high gm VHF type and "loves" to oscillate.

[Shoog]

Thanks for all the reply's.
I will do some experiments when I get the time. Should be fun to get a simple tube circuit working.

Shoog