[Amps] Fwd: Linear Amplifier Tuning---PROPERLY!

[Eddy Swynar]

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  


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Begin forwarded message:

> From: Eddy Swynar <deswynar at xplornet.ca>
> Date: December 19, 2011 8:32:49 AM EST
> To: amps at 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