>
>I have acquired a Spectraphysics Laser amp case with 2x4CX350 (presumeably in
>good condition) and I'm about to embark on a rebuild job for 6 meters.
>My current design plan (based on input from several club-members) is as
>follows:
>The two tubes in parallel, grounded grid2; -300V cathode;
This means the grounded screens are relatively pos. 300v with respect to
cathodes. To obtain optimal SSB output, one needs 400v on the screens.
// 4CX350s have a delicate screen. Be sure that the screen potential
is derived from a string of zeners biased through a resistance connected
to the anode supply. The resistance should be carefully chosen to allow
no more than150% of the typical screen current. . A heavy duty screen
supply can destroy a 4CX350 is seconds.
>This is variable -30 to 300v
>grid1 bias; 2400V (350mA) EHT (40uF/2500V MP cap.); tuned input with 6-10 dB
>attenuator, pi-tank.; various control and interlock electronics and
>startup/inrush timing.
>
>I have seen several (triode) designs using 20KV doorknobs, wouldn't about 5KV
>suffice?
RF current rating is a considerable consideration.
>
>HV transformer and HV Cap. are in hand, and pretty much defines the supply
>performance parameters.
>
>I hope to see some ... 1 KW PEP in SSB. ....
Not likely with reduced screen potential.
Other Comments:
- Use a 20 ohm or so 20w glitch resistor in series with the hv source.
- For optimal stability, connect a few hundred ohm RF term. resistor
between the grid and the cathode (approx. 500pF cap. in series). Use
minimum inductance leads.
- Avoid grid current like the bubonic plague
>
- later, Peter
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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