[ARC5] Hello Smart People: Output Network "L"

[Geoff]

If this is grid driven have you checked the neutralization?


----- Original Message ----- 
From: "Ian Wilson" <ianmwilson73 at gmail.com>
To: "David Stinson" <arc5 at ix.netcom.com>
Cc: "ARC-5 List" <arc5 at mailman.qth.net>; <milsurplus at mailman.qth.net>
Sent: Sunday, April 15, 2012 10:58 AM
Subject: Re: [ARC5] Hello Smart People: Output Network "L"


> I've seen similarly puzzling effects with an 813 in a pi network
> using an inductor with switched taps. The thing would dip weakly and
> not produce expected output. Changing to another tap close by would
> make more change than I would expect.
> 
> I have tried taking all the power away and putting a resistor to ground
> in place of the tube, then looking into the pi network with an antenna
> analyzer. These results also indicated that something was not right.
> Replacing the RF choke made a noticeable difference, and at the time
> I thought there was a resonance.
> 
> On reflection, however, I suspect that what is happening here is that
> there is a grounding problem and/or a stray capacitive or inductive path.
> Changing the pi network coil slightly changes the phase shift around the
> network and this in turn combines with the stray to produce odd effects.
> 
> This sort of effect would be cancelled out by neutralization although
> unless it's a pure capacitance that would only be effective over a small
> frequency range.
> 
> This is still a theory, but since the observed effects can't arise from a
> simple pi network, there have to be other L/C in the circuit somewhere.
> 
> 73, ian K3IMW
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