[Amps] 4CX1500 QSK

[Mark Hill <g4fph@mjha.co.uk>]

Rich,
Karl-Arne,

Many thanks for the suggestions.  Having looked at the circuits for the 
amplifier section, I think leaving the screen Voltage present at all times 
and switching the grid bias would be easiest.  Prompted by your circuit 
idea Rich, I have dug out a suitable power FET and OPTO that should handle 
switching duties.

Rich, it seems as though this particular TX /amplifier has been optimised 
for very low IMD at the 1 kW level - probably because there were lots of 
them in close proximity to one another.  The manual quotes IPs as better 
than -36 dB on either of two tones (CCIR 326-2).  The operating parameters 
seem to be taken more or less straight from the Eimac data sheet for the 
valve.  I noted you point about the valve being capable of producing more 
Watts.  I may try just a few more Volts on the screen out of curiosity, but 
the low IMD probably betters my triode units and will be good for local rag 
chews and digital modes.

Karl-Arne, the Collins sounds like an interesting unit.  I hope I don't 
come across one at a bargain price - it would be terrible to have to choose 
between a lovely wife and a 'tube with handles'!

Regards.

Mark.


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