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In Reply to: RE: 845 Interstage A2 Question posted by danlaudionut on September 06, 2014 at 06:55:41
Dan,
Your bank balance must be "fat". Good interstage "iron" is EXPENSIVE. Tubelab's "PowerDrive" solves the positive grid current problem economically.
BTW, the idea was developed for an 845 setup. ;>)
Eli D.
Follow Ups:
Read the benefits of a CCS in the plate. What about an LM334 at the cathode instead?
Agree with Eli, it seems like a lot effort & $$$ with the IST. See Andrea's design here.
Edits: 09/06/14 09/07/14
You will need to provide a stable negative bias supply, and that's it. You can choose to have a regulated or unregulated supply, and the only thing that really matters is that it must start simultaneously with the main power supply.
The grid current is coming from the main power supply, because as you approach 0V the grid starts drawing more current which at 0V becomes "important" and as the grid is driven more positive, it will draw more current.
Now in order to drive the control grid positive, you will need to be able to drive it with some power, which translates into voltage swing and current swing into a given load (the load is the control grid).
You should check the 845 datasheet for exact details on g1 current for a given positive voltage. The 300B will certainly be able to drive the 845, but exact details depend on the grid current for the wanted swing, the transformation ratio of the interstage transformer, and thus the operating point chosen for the driver tube.
Once you know the necessary operating point, you need to make sure your interstage transformer can handle that much current.
http://rh-amps.blogspot.com/
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