>
>Saturday 10th October 1998
>
>Hello all
>
>I enjoyed a visit to Rich Measures AG6K web-site - thanks for
>the interesting info. Rich. (I also enjoy this reflector when
>you guys can't agree on something!)
>
>Thinking about neutralising a tetrode for 1.8-30MHz use, I
>noted the method proposed by Rich (disconnect the tank cct.
>and terminate with non-inductive R equal to the load impedance,etc)
>- I was wondering if the simpler method (which I've only used
>once with a 2 x 4CX250B amp. for 144MHz) would give as accurate
>a setting ?
>The method is to feed 2-3W of, say, 21MHz RF, INTO the 'RF output'
>connector (with the HV and G2 supplies off, but filament and G1 bias
>'on' and the T/R coax relays activated), then adjust the
>'Neutralising' variable capacitor for minimum RF voltage developed
>across the input (grid) tuned circuit ?
>(I'm not sure if the G1 bias should be 'off' or 'on')
>
The grid bias potential does not seem to matter. // As I see it, the
problem with trying to neutralize by feeding the RF signal backwards is
that there is no way of tuning the grid's roller inductor to resonance.
This is not insignificant because the grid must be resonant Before
zeroing in the neutralization adjustment -- the reason being that the
grid roller-L provides the essential 90 degree phase shift supplement to
the 90 degree phase shift through the anode's capacitive. voltage
divider, thereby producing the needed 180 degree phase shift.
- later, Chris
Rich. Measures. Web site: www.vcnet.com/measures
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