Cathode Followers and Pass Tubes

[denny9167]

It would be interesting to take a reading to some old papers. I found myriads of data from old papers freely available on the net. The most juicy IMO is one from Hunt and Hickman "On Electronic Voltage Stabilizers" from 1939. Its the oldest I could find and many future literature makes reference and take concepts from it. I suggest to take a reading: it is very deep and explanatory.

Another one is "Basic Theory and design of Electronically Regulated Power Supplies" by A. Abate Proceedings IRE July 1945.

Still more on "Stabilized Power Supplies" M. G. Scroggie, Wireless World october 1948.

One more is "Design of Electronically Regulated Power Supplies" by Ben Penners and W. Davis Radio, feb. 1947.

Sounds like interesting reads.

 

[denny9167]

Under heavy load the grid of the passer needs to be pulled up close to the cathode.
So for example a 6AU6 or whatever is used, its plate resistor needs to go to a much more +ve place.
In common designs that is often the raw DC out of the Rectifier/Filter combo.
Some designs pull that up even further.

Some volk try running the subject plate to the regulated +ve lead. Sometimes in such designs
the regulator locks up & refuses to start.😱

I quite agree, I nearly always tie the load/current source resistor of the control tube driving the pass to the unregulated side!

 

[denny9167]

I've been using this US Navy manual for along time for understanding regulated power supplies, but it deals with many other curcuits as well, some solid state also.

US Navy Handbook

https://www.dropbox.com/s/5yrxb472uw9w9cv/NAVAER1615191.pdf?dl=0

 

[v4lve lover]

I'm not too fond of the added complexity of a cathode follower to drive pass tube grids, for normal tubes that have non-existent grid current its much easier to use a 5-10mA CCS with a frame grid construction pentode error amplifier like EF184 or E83F. Current source loading allows for higher gain, and none of the drawbacks of multiple tubes.

If you use a high impedance current source like a PNP cascode fed from the single wave rectified pass tubes heaters, you can get amazing results.


If you want to do something with cheap tubes, you can use two PCF80 one as a long tailed pair with 85A2 reference, feeding a pentode half VAS and use the second triode for follower duty. You would need a 0A2 reference tube to keep the cathode of the pentode VAS at +150V

Heaters for the PCF80 would be referenced to +200V or so to keep all the heater isolation within spec for up to 350V output voltage.