[Amps] SB-220 bias question

[DF3KV]

Circulating current is not increasing because drive is reduced, but because
Q is increased (L remains the same) by tuning for lower output at higher
voltage.

73
Peter

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Bill, W6WRT
Sent: Sonntag, 30. August 2009 17:16
To: amps at contesting.com
Subject: Re: [Amps] SB-220 bias question

ORIGINAL MESSAGE:

On Sun, 30 Aug 2009 10:12:31 -0400, "Joe Subich, W4TV" <lists at subich.com>
wrote:

>If you change the network by changing the plate load impedance 
>as you do when you run 1000 watts in the high voltage position 
>the VALUES of the capacitors must change since the value of the 
>inductor is fixed.  

REPLY:

There is your fundamental error. Simply by reducing the drive (without
retuning), you DO NOT change the impedance the network presents to the tube.
The
impedance is the same and the Q is the same. Only the amount of energy fed
to
the network changes, and of course the efficiency. Basic physics.

You can easily prove this for yourself. Tune up at max power, measure any RF
voltage or current anywhere in the output network, including the antenna,
and
then reduce the drive. The RF voltage and/or current will decrease linearly
with
the reduction in drive. That's why they call them "linear" amplifiers. 

To insist that circulating current INCREASES when drive is reduced is utter
nonsense. Period.

73, Bill W6WRT


_______________________________________________
Amps mailing list
Amps at contesting.com
http://lists.contesting.com/mailman/listinfo/amps