[Collins] 30S1 Screen voltage

[Dutch Maurer WB7DYW]

Of course I changed the cap and for good measure I also replaced all the output transistors...

73's Dutch WB7DYW
CCA Member #918

Success is not a place in time, it is an attitude…

--- On Sat, 1/8/11, Dr. Gerald N. Johnson <geraldj at weather.net> wrote:


From: Dr. Gerald N. Johnson <geraldj at weather.net>
Subject: Re: [Collins] 30S1 Screen voltage
To: collins at mailman.qth.net
Date: Saturday, January 8, 2011, 2:10 PM


Dutch, have you increased the value of the screen supply capacitor to 
improve its dynamic regulation? I found that made the 30S-1 at MARS 
station K4WCC have a much better punch on SSB and high speed CW.

My concern for the higher screen voltage is the output tank. Without 
changing coil taps for the higher plate current the tuning has to be 
away from the original designs, presenting a lower input impedance to 
the tube. With the Pi net that means reducing the value of the loading 
capacitor and increasing the value pf the tuning capacitor. With a fixed 
RF voltage on the input that means increasing the current in the tuning 
capacitor and the coil, increasing the circulating current. I wonder 
about the loaded Q which is important for harmonic reduction. Lowering 
the loaded Q increases harmonics, and makes tuning less critical. E.g. 
greater bandwidth.

Then changing the operating parameters of the tube will also change the 
cathode impedance and the input matching networs in the 30S-1 do show 
some impedance transformation already. Has anyone running the higher 
screen voltage adjust the input to output C ratio on those to improve 
the match seen by the driver?

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.

On 1/8/2011 7:34 AM, Dutch Maurer WB7DYW wrote:
> I run a 30S-1 with this mod on the Sunday CCA net for hours at a time and it works fine, the 4CX1000 was designed to run with 325 volts on the screens and the amp was built to handle it....
>
> 73's Dutch WB7DYW
> CCA Member #918
>
> Success is not a place in time, it is an attitude…
>
>
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