Pentode Cascode CCS

[croccodillo]

Ciao,

I just built this solid state CCS, and now it is under test.
Q1 and Q3 form a CCS, with a current from a minimum of 0,8 mA@30V (between Cathode and GND) to a maximum of 1,3mA@600V; the current is needed to feed in the correct way the LM336-5 regulator, that needs not less than 0,6mA and not more than 10mA.
The 5V across IC1 are then used to feed the Q2 device, a P mosfet: at its source pin, then, you'll have about -1V than Cathode pin.
The CCS current is given by the R2 value.

On the weekend I'll build a circuit like this, a parafeed stage with the upper tube used as a pentode CCS.

I'm not so skilled with tubes and pentodes, so my question is: is the upper tube connected in the right way to work as a pentode?
The B+ voltage will be of about 600V (something less), the CCS current fixed at 100 mA and the working point of the lower tube set to 300V.

Thanks in advance,
Giovanni

 

[AndreasS]

Pentode as CCS

http://www.jogis-roehrenbude.de/Leserbriefe/AndreasS-8608-VV/6808.htm

regards Andreas

 

[croccodillo]

Dear Andreas,

thanks for your answer to my post: I looked at your schematic, here,
and I have a question:
which is the +Ug2 voltage? Assuming +Ub = 600V, whih voltage should I use?

Thanks and best regards,
Giovanni Albergoni

 

[Shoog]

Thats the way I told you to do it about a month ago.

There seems to be only a few solutions to using a pentode as a CCS's, and it seems that its either this way or Gary Pimms Pentode CCS - which isn't a whole lot more complex.

When are you going to make up your mind and just build it. Only testing on the bench will tell you if the result is satisfactory.

Shoog