Walter Dail wrote:
>
> Hello All,
> I have a question regarding using a grid swamping resistor
> on a tetrode amp. I have been building a twin cavity amp for
> 432 Mhz using a 4CX250B tube. I understand that instead of
> neutralizing a grid driven amp a grid swamping resistor may be used.
> These are found in all the handbooks, etc. showing 2m amp
> schematics. However, in the 1985 ARRL Handbook, page 32-8,
> "A Tetrode UHF Amplifier" it does not show such a resistor
> in the input compartment. They are using 10W drive also.
> But I noticed in the grid PS they have a 100 ohm 2W resistor in the
> line that feeds the grid bias. Is this what they are using? What gives?
> Is the Handbook wrong and a grid swamping resistor should be added?
>
> Comments please,
> Walter Dail -KT4JA
Hi Walter,
I have built several of those type amps using the 4cx250 tubes. The
handbook is correct, you will not need a swamping resistor. However I
recommend using good mechanical construction in isolating the output
from the input. I have had folks bring me amps that they built and
wonder why just waving their hand over the RF deck causes the tuning to
change..I am serious. I am no doctor but have to believe this could be a
serious health hazzard. Its a little harder to keep the RF contained at
432 so exercise caution.
Ron W4WA
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