re: Alpha type toroidal input circuit
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A follow up comment regarding the addition of
the series R and a UF Diode in parallel with the
tube cathodes in an Alpha type input circuit.
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It's obvious the opinions vary quite a bit about the
input toroidal transformer, terminated with a
resistor network paralleled with the tube cathodes.
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Although not the best circuit, I thought the
approach a unique idea that IMO does work to
obtain the expected results. I have not used this
layout in an rf amplifier, but I have used it to solve
some problems in very reactive NMR probes with
great success. A while back you might remember
my inquiries about the Maxcom Antenna unit, which
ends up being a similar type circuit. Practical
solutions work and this circuit is very adaptable
to other applications.
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The addition of the series R and UF Diode would
probably not be just plug & play into an existing
Alpha type input circuit. Someone with the time,
patience and test equipment will have to try and
make it play without grief.
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I have tried and used the toroidal input xmfr to a
swamped R& LC circuit with much success. A
classic layout is the 4cx250 circuit shown on the
sonic server. It does require band switching..
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thanks to all who replied
cheers
skipp
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> From: "Steve Thompson" <g8gsq@qsl.net>
>Steve asked:
>". Has the shunt diode idea been tried in practice?
> Did it work above 10MHz? If yes, please let me know
> which brand and part # was used."
> In the late 50's, I think it was W6JAT, who worked for
> Eimac that published a circuit of a shunt diode across the
> input circuit of a 3-1000 amp, using a 6X4. The diode did
> not have a series R, although it would have an internal
> impedance. Circuit was claimed to work fine. I always had
> a big question mark about it.
I can imagine it working with a vacuum diode. No minority
carriers and storage time etc. I've no idea what capacitance
a power rectifier tube represents.
Steve
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