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

[Carl]

----- Original Message ----- 
From: "Frank" <frankkamp at att.net>
To: <TexasRF at aol.com>
Cc: <amps at contesting.com>
Sent: Thursday, December 22, 2011 1:32 PM
Subject: Re: [Amps] Fwd: Linear Amplifier Tuning---PROPERLY!


> TexasRF at aol.com wrote:
>
>>Hi All, it makes no sense to not peak the tune C as the last step in a
>>matching procedure.
>>
>>The tuning network is fully adjustable, allowing a match from your nominal
>>50 ohm load to what ever plate load impedance you want to use. If the tube
>>needs  2000 ohms for best efficiency and power output, it is a simple 
>>matter
>>to provide  that. But, the transformed impedance is resistive only when 
>>the
>>complete network  is resonant. The only way that can happen is when the
>>plate tune C is adjusted  last, for maximum power transfer. The complete
>>network includes all sources of  reactance, including tube output C and 
>>stray C as
>>well as the effect of the rf  choke and tank inductor and tune C.
>>
>>When you tweak the tune C for maximum output, you are making all of the
>>reactance contributors parallel resonant, leaving only a resistive load 
>>for
>>the  tube.
>>
>>Sure the plate load impedance changes when you tweak the tune C, that is
>>what is supposed to happen. Over coupling slightly is just another way to 
>>say
>> that the plate load impedance is reduced slightly. If you don't end up
>>with the  desired over coupled value, then the plate load C is not set to 
>>the
>>required  capacity and needs further adjustment.
>>
>>Operating a tube into a reactive load just doesn't make any sense in my
>>mind. It may not be reactive enough to hurt anything but how can it help 
>>in
>>any  way?
>>
>>Standing by for other view points and arguments.
>>
>>73,
>>Gerald K5GW
>>
>>
>>
>>
> That is the ticket!  Tune for max smoke at the antenna!  It works for me.
>
> I can see how you can improve IMD 2 or 3 db by agonizing over the
> "proper way to tune" but your probably already at 20 to 30 db IMD to
> start with.  That 3 db will never be noticed by anyone except the fellow
> looking at the lab equipment.


Hmmm, Im glad I dont operate near you!  Anybody with an amp with that poor a 
level of IMD
should have his license cancelled. Except for sweep tube, old tetrode, amps 
and some poorly
designed SS, IMD greater than -30 is the norm these days and better ones are 
in the -40's.

BTW, 3dB is equivalent to doubling or halving the power and if you cant hear 
that go see a hearing specialist.

Carl
KM1H