Shawn,
Thanks for your comments.
The 4CX1000 on 2m that I saw in the 1990 ARRL Handbook pg. 31-57 uses
a 680 ohm 2W resistor for swamping in the grid bias (R1).
I have no other choice (for mechanical reasons) than to go this route.(using
a swamping resistor as opposed to neutralization). I have had fair luck
using a swamping resistor in the past, just I dunno on 432...
Thanks,
Walter
At 06:55 AM 9/30/97 +0700, you wrote:
>AT this frequency you might be better off trying to use the screen to give
you the isolation from plate to grid.
>Several broadcasters do this with big tetrodes on the FM band. There is a
design using a 4CX1000 on 2M in
>one of the handbooks that uses this approach. It complicates the metering
and power supply setup but it can
>work.
>
>The swamping resistor doesn't always work. We had a devil of a time
getting a 4-1000 to settle down at 6M.
>Turns out the problem was a resonance from the plat tune cap thru the plate
to the grid. The resistor actually
>helped it, at 110Mhz. We fixed this one by using a stainless steel strp
from a hose clamp, the slots added a
>small amount of inductance that swamped the 110Mhz energy real nice. Grid
resistors are more for matching
>than helping stability, at least in my experience. They do help but they
are not the end all fix.
>
>
>
>On Tue, 30 Sep 1997 09:36:55 -0400, 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
>>
>>
>>
>>--
>>FAQ on WWW: http://www.contesting.com/ampfaq.html
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>>
>
>
>de Shawn
> N7LQ (formerly WB7TDI)
>
>DM09dn & DN01fa
>
>
>
--
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