[AMPS] 4-400 operation parameters and such
Tue, 5 Aug 97 19:21:18 -0700
>I'm further along in my building of my first grid driven amp and could
>use some input.
>Could someone give me some idea of what voltages I should be looking at
>and maybe the currents as well.
>I have the parts to build a solid 4100 volt supply which is CCS at 750
>mils. Have tested it and all seems well.
>Running 600 mils with a pair of 4-400's is well within plate current
>specs and will give me about 2400 input ( not considering any E drop due
>Any suggestions what to run for screen Voltage? I can do 400-500 volts
>easy with parts I have.
A screen supply of 750v to 800v is good for Class AB1 linear service,
especially with 4.1 kV on the anode. The problem with using lower screen
V is that the peak emissive capability of the 4-400 cathode can not be
realized without driving the tube into the (non-linear) grid current
region. Perhaps you could use a fullwave v doubler to secure the higher
voltage. (It takes little avg. screen current for a pair of 4-400s.)
>How about grid bias?
around 135v of bias for operate, 200v for cutoff. Using a grid term. R
of 50 ohms, you would need a driver that can produce 185w. Using a grid
term. R of 200 ohms, driven through a 1 to 4 step-up (bifilar)
transformer, you would need about 50w of drive.
- For best stability, I would directly ground the screen terminals and
connect the screen supply between the fil. CT (cathode return) and
chassis-ground. A grounded screen circuit is shown on my Web site:
There is also an electronic-switched Class AB1 grid bias supply and a
short-circuit proof regulated screen supply. .
R. L. Measures, 805-386-3734, AG6K
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