Hi Guys,
Obviously this is a VERY interesting question, & one which I really & truly
believe that not much thought is given to by the amplifier-using / designing
community, judging by the e-mails that I received...
I've received a total of FOUR responses re. the need / desirability (if any) to
"re-tweak" the plate tuning control after slightly over-coupling the loading
capacitor during the tune-up procedure. Of these four, I got the distinct
impression that two were rather non-committal at best, one stated that the
tuning capacitor should be re-peaked, and the fourth stated that no, the
advanced loading should be the final step...
Interesting! And I thought that I was the one who was confused! Hi Hi
~73~ de Eddy VE3CUI - VE3XZ
***********************************************************************************************************************
Begin forwarded message:
> From: Eddy Swynar <deswynar@xplornet.ca>
> Date: December 19, 2011 8:32:49 AM EST
> To: amps@contesting.com
> Subject: Linear Amplifier Tuning---PROPERLY!
>
> Good Day All,
>
> A stupid question to many, no doubt, but one that I'd like some clarification
> on, at long last...
>
> Specifically, anything that I've read in different literature & in on-line
> write-ups regarding the proper tuning of grounded-grid linear RF amplifiers
> makes note of one, final step in the tune-up procedure: specifically, one is
> to reduce the plate loading capacitance (and thereby slightly over-couple the
> amplifier to its load) such that power output is lowered by some 5-10%...
>
> Correct?
>
> Yet, nowhere is this instruction followed by anything advising one to
> subsequently "re-peak" the plate tuning capacitor in kind, as I instinctively
> always do (force of habit, I guess).
>
> Is it a requirement to do just that, i.e. to tweak the plate tuning after
> this deliberate over-coupling...? Have the authors of these write-ups simply
> assumed that that is, indeed, the case, & have therefore not made specific
> reference to this process...? Or does one truly advance the loading capacitor
> to lower output---and then leave well enough alone...?
>
> I ask this because I am finding that the tuning requirements of my homebrewed
> 2x813 kilowatt can be VERY exacting: improperly adjusted, & the keying from
> it on CW can sound inordinately hard---almost clicky. I'd like to do things
> right with it, both for the sake of the tubes, as well as for others on the
> band who might be operating close to my frequency...
>
> Thanks in advance,
>
> ~73~ de Eddy VE3CUI - VE3XZ
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