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[AMPS] Length of Anode Lead To Tuning Condenser in a Linear Amplifier?

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Subject: [AMPS] Length of Anode Lead To Tuning Condenser in a Linear Amplifier?
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Date: Sun, 22 Jul 2001 15:01:47 EDT
>From what I have been able to gather over the years, in the output circuit of 
a GG Linear Amplifier it is good practice to keep the length of the lead as 
short as possible from the Anode of the tube to the Tuning Capacitor of the 
Pi-Net output circuit, and to mount the Tuning Capacitor as close as possible 
to the base of the tube to keep ground return currents as short as possible 
from plate to grid grounding point? If that is the case then the best 
practice would be to mount a Vacuum Variable Capacitor vertically as close to 
the tube as possible without bumping into the glass chimney for a glass tube 
or bumping into the anode of an external-anode tube? With an external-anode 
tube like the 8877 the distance between them could be practically zero. Has 
anyone done any research into the stray effects of hanging a large DC 
Blocking Doorknob Capacitor in line between the Anode and the first Tuning 
Cap? I imagine depending on the construction of the DC Blocking Capacitor it 
could introduce some significant stray inductance and capacitance into the 
circuit? This effect could be greatly reduced as well as size of the Blocking 
Cap if a Ceramic Chip Capacitor assembly could be used at this point. If the 
distance in the Anode circuit were reduced to near-zero would this 
significantly raise the VHF parasitic resonant frequency of the circuit? Is 
it always easier to damp out a VHF parasitic if its frequency is raised? 
Would a parasitic suppressor still be needed? 73 Todd Roberts WD4NGG .

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