[Amps] Linear Amplifier Tuning---PROPERLY!

[Jim W7RY]

http://www.w8ji.com/loading_amplifier.htm

73
Jim W7RY


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From: "Eddy Swynar" <deswynar at xplornet.ca>
Sent: Monday, December 19, 2011 5:32 AM
To: <amps at contesting.com>
Subject: [Amps] 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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