RE: impedence of CCS mu output

Posted by VT4C211 (A) on April 11, 2010 at 17:26:36

In Reply to: impedence of CCS mu output posted by bobbyj on April 7, 2010 at 16:55:01:

I've seen those type of mu-followers over the years, and I tried a few of them including using a pentode, with floating filament and screen supplies all regulated, various depletion mode FET's, etc. I settled on a simple circuit using a HV FET and an LM431 (which are useful up to 500KHz+).
The output is DC current, all AC is suppressed. Flat from DC -3dB to 450KHz. R1 sets plate current, here about 5mA. Set it to a linear range for the tube used. The voltage swing from a tube at low current is very wide, from B+ (from 500 - 600V) down to maybe 35V with a 6SN7 at 3mA. Perfect for driving wide swing 845, 211 and other low mu tubes .
Power output is dissipation limited by the MOS-FET. The FET should be able to handle most any kind of load, maybe even the transformer. Use a fuse in the power supply to reduce smoke formation. Add 50% margin to the voltage rating of your FET. This circuit should perhaps better be called a Current Controlled Voltage Source? I placed the components on to of the FET and attached it with insulating thermally conductive double sided tape to the chassis. A low gate charge FET also has low feedback capacitance reducing AC from the PS. C1 is not so critical, use small 10uF electrolytic or whatever. Zener diode will protect the gate and the LM431. I got the basic circuit idea from the LM431 data sheet.

Output impedance of a follower is typically Rp/u.

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Follow Ups Full Thread

Topic - impedence of CCS mu output - bobbyj 16:55:01 04/7/10 (27)

RE: impedence of CCS mu output - VT4C211 04/11/1017:26:36 04/11/10 (4)

RE: impedence of CCS mu output - dave slagle 21:18:39 04/11/10 (3)

RE: impedence of CCS mu output - VT4C211 21:29:48 04/12/10 (2)

RE: impedence of CCS mu output - Michael Koster 23:50:46 04/12/10 (1)

RE: impedence of CCS mu output - VT4C211 19:01:53 04/15/10 (0)

RE: impedence of CCS mu output - Michael Koster 22:56:52 04/7/10 (13)

RE: impedence of CCS mu output - Mike C 12:34:59 04/12/10 (1)

RE: impedence of CCS mu output - Michael Koster 10:14:57 04/14/10 (0)

RE: impedence of CCS mu output - bobbyj 11:22:37 04/8/10 (3)

RE: impedence of CCS mu output - Michael Koster 12:57:26 04/8/10 (2)

RE: impedence of CCS mu output - Satanpatiently 14:33:37 04/8/10 (1)

RE: impedence of CCS mu output - Michael Koster 08:02:47 04/9/10 (0)

Thank you for that great explanation. nt - Tre' 10:14:22 04/8/10 (0)

Michael, to split hairs... - Allen Wright 06:13:59 04/8/10 (1)

RE: Michael, to split hairs... - Michael Koster 08:11:19 04/8/10 (0)

RE: impedence of CCS mu output - Joao 23:52:51 04/7/10 (3)

RE: impedence of CCS mu output - Michael Koster 10:06:33 04/8/10 (2)

RE: impedence of CCS mu output - reVintage 05:19:52 04/10/10 (1)

RE: impedence of CCS mu output - Michael Koster 08:24:29 04/10/10 (0)

RE: impedence of CCS mu output - Tre' 17:04:47 04/7/10 (7)

RE: impedence of CCS mu output - bobbyj 18:24:37 04/7/10 (6)

RE: impedence of CCS mu output - Tre' 18:57:48 04/7/10 (5)

RE: impedence of CCS mu output - bobbyj 20:18:13 04/7/10 (3)

RE: impedence of CCS mu output - Tre' 20:40:39 04/7/10 (2)

RE: impedence of CCS mu output - bobbyj 10:15:02 04/8/10 (1)

RE: impedence of CCS mu output - Tre' 10:20:13 04/8/10 (0)

Here's a helpful calculator - Tre' 19:02:17 04/7/10 (0)

Follow Ups

RE: impedence of CCS mu output - VT4C211 04/11/1017:26:36 04/11/10 (4)

RE: impedence of CCS mu output - dave slagle 21:18:39 04/11/10 (3)

RE: impedence of CCS mu output - VT4C211 21:29:48 04/12/10 (2)

RE: impedence of CCS mu output - Michael Koster 23:50:46 04/12/10 (1)

RE: impedence of CCS mu output - VT4C211 19:01:53 04/15/10 (0)

RE: impedence of CCS mu output

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