[Boatanchors] 30S1 bis query

[Gary Schafer]

Hi Jim and all,

I just looked at the schematic (been a long time since last) and you are
right it does have a tuned input network. The L network however is on 10
meters and pi on the lower bands on the schematic I have. I also see a
second pi section with input and output capacitors the same on 80 meters
before the pi network.

I see that the input impedance to the tube is apparently lower than the
impedance from the input connector. The output capacitors of the pi network
(the one at the tube side) is smaller than the input side capacitor of the
pi network. That indicates that the tube is lower impedance than the other
side of the pi network.
Most grounded grid tubes have an impedance greater than 50 ohms which
affords a larger capacitor at the tube end of the network and a smaller one
on the input side.

So I would guess that the amount of capacitive reactance needed at the tubes
cathode to afford low distortion is greater than what can be used to match
the tube and still maintain a proper Q in the circuit. The special cable
length probably transforms the reactance that the exciter output capacitance
provides to a low value at the input of the 30S1. Better to have the low
reactance value at the input than have it at the exciter and maybe
transformed to a high value at the amp with a random length cable.

73
Gary  K4FMX

> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> bounces at mailman.qth.net] On Behalf Of Jim Wilhite
> Sent: Wednesday, August 16, 2006 9:29 PM
> To: boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] 30S1 bis query
> 
> > As to the 20' cable to the exciter;
> 
> > The 30S1 does not have a tuned input circuit.
> 
> 
> My diagram of the 30S1 shows a tuned input, Pi net on the upper 3 bands
> and
> L network on the lower bands.
> 
> 73  Jim
> W5JO
> 
> 
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