[Boatanchors] 30S1 bis query

[Jack Taylor]

One source I discussed the 30S1 input cable length situation with was of the
opinion it was an old broadcast transmitter 'trick' to improve output
linearity.
The cable length is determined by wrapping a coupling loop around the
outside of the cable and, driving a scope.  He didn't specify but I assume
one looks for the 'best' audio waveform when adjusting cable length and
with the transmitter keyed.  I've not tried this so can't comment
one way or the other.

Gary thanks for reminding me to revisit the value of the screen supply fuse.
I've installed a 1 amp slow blow and so far it's holding.  As a guess I'd
say
the cause of the fuse blowing and the various relay contacts sticking could
be traced back to the intermittent contact of the bias pot wiper which
allowed
zero bias to the 4CX1000A.  This in turn caused excessive plate (and
probably screen) current to flow when in the SSB position.

73 de Jack  --  N7OO

----- Original Message ----- 
From: "Gary Schafer" <garyschafer at comcast.net>
To: "'Jim Wilhite'" <w5jo at brightok.net>; <boatanchors at mailman.qth.net>
Sent: Wednesday, August 16, 2006 7:09 PM
Subject: RE: [Boatanchors] 30S1 bis query


> 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
>