On Thu, 3 Sep 1998 13:29:00 +0200 pfrenning@idc.com writes:
>
>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; 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.
The grounded grid design is viable and was used commercially by Tokyo
High Power in the ham market. However it was predominantly as a way to
dump excess drive power from the average 100W exciter.
I use a converted National NCL-2000 on 6M which uses a pair of 8122
tetrodes at 1200W out. The 8122 has very similar specs to the Svetlana
4CX400A.
I am using a swamped grid input with the addition of a small tuned
circuit to tune out reactances. The swamping resistance can be anywhere
from 20 Ohms or so up to about 200 Ohms dependent upon drive available.
With that degree of swamping neutralization is not reuired and the amp is
completely stable.
Another advantage in using a more conventional circuit is that it is
simple to include the G3SEK design screen regulator for best IMD since VR
tubes and Zeners do not have the low impedence required for ultimate
performance.
I drive the amp to full power with 15W of drive from a Down East
Microwave transverter.
>
>I have seen several (triode) designs using 20KV doorknobs, wouldn't
>about 5KV
>suffice?
Many of the 20KV doorknobs as used in ham equipment are not RF rated and
are designed for TV and industrial use. A 1000pf/5KV RF rated doorknob
will work just fine.
>
>HV transformer and HV Cap. are in hand, and pretty much defines the
>supply
>performance parameters.
>
>I hope to see some 800W key-down/1 KW PEP in SSB from the Beast.
According to Eimac that tube is rated at 385W PEP with 2200VDC and 290ma.
I would use that as a start and I would also defer to Ian, G3SEK, on the
ideal parameters in keeping with the goal of clean signals in Europe!
Good Luck
73 Carl KM1H
>
>Any thoughts and/or gotcha's from the group on this? Or links to
>similar
>designs?
>
>Best regards
>
>Peter Frenning, Program Director.
>European Internet Team
>IDC Scandinavia
>Ph.: ++45 39162237; Fax: +45 31184448
>email: pfrenning@idcresearch.com
>email(private): oz1pif@get2net.dk
>WWW(private): http://hjem.get2net.dk/oz1pif/index.htm
>
>
>
>--
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>
>
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