I was taking IMD and other measurements long before the Internet got
popular. Ive also made the results available enough times on amplifier
forums the past 15 or so years that I would have thought it would have sunk
in by now. Instead the subject keeps coming back over and over again. Even
my first wife learned faster!
For the SB-220, IMD is 2-3dB better with the grids as designed by Heathkit.
A small part of that may be the 100W less output affecting the PS regulation
which isnt that good to start with. Going to 330 uF caps in the PS helps a
bit. CDE 330uF 450V 105*C 381LX series fit perfectly into the existing
blocks. Going to 75K equalizers adds another bit less current drain.
Adding an attenuator in the RF path between the input network and the tube
further reduces power but a 10 Ohm 10W resistor that is non inductive at 10M
is hard to come by and 2W carbons are not exactly growing on trees these
days nor are they resistance stable with RF over time. Using MOX resistors
adds some inductance that has to be tuned out on 10-15M and that is a PITA
and not worth the effort IMO.
Carl
KM1H
----- Original Message -----
From: "Fuqua, Bill L" <wlfuqu00@uky.edu>
To: "Carl" <km1h@jeremy.mv.com>; "Herzog" <herzog@frontiernet.net>;
"Ham-amps" <amps@contesting.com>
Sent: Sunday, August 02, 2009 12:13 PM
Subject: RE: [Amps] grounding grids
It is very helpful to question what has been done in the past so we can
learn from it.
Making real measurements helps also. I did not see the details of your
experiment
but comparison with directly grounded grids and the original circuit in the
same amplifier
would be useful. I have not seen all the email exchanges on this subject
and I may have
missed the details.
I after my emails are downloaded to my office computer I can't view them
with my home
computer.
73
Bill wa4lav
________________________________________
From: Carl [km1h@jeremy.mv.com]
Sent: Sunday, August 02, 2009 10:38 AM
To: Fuqua, Bill L; Herzog; Ham-amps
Subject: Re: [Amps] grounding grids
Mine is to leave things alone after performing the PM and other improvements
I mentioned earlier.
I get a kick out of a small minority always thinking they are better than
the design engineers. Yet when it comes to providing more than talk the
silence is deafening.
I also mentioned earlier that my spectrum analyzer tests showed a small IMD
improvement with the grids as built. My testing covered 80 to 6M. This was
later confirmed by Jacks report from the Drake L-4 designer.
Carl
KM1H
----- Original Message -----
From: "Fuqua, Bill L" <wlfuqu00@uky.edu>
To: "Herzog" <herzog@frontiernet.net>; "Ham-amps" <amps@contesting.com>
Sent: Sunday, August 02, 2009 12:24 AM
Subject: Re: [Amps] grounding grids
> The question we should ask now what are our preferences in grounding
> grids.
> Mine is as direct to ground as possible with the least series impedance.
>
> 73
> Bill wa4lav
> PS Has the gentleman trying out the 4cx250Bs in grounded grid (control
> grid connected to cathode) gotten any results?
> I would like to know how it turned out.
>
> 73
> Bill wa4lav
>
> ________________________________________
> From: amps-bounces@contesting.com [amps-bounces@contesting.com] On Behalf
> Of Herzog [herzog@frontiernet.net]
> Sent: Saturday, August 01, 2009 6:44 PM
> To: Ham-amps
> Subject: [Amps] grounding grids
>
> RE: What makes you think that the impedance between the grid and
> common changes by a factor of 10:1 between 3.5 and 29.7 MHz?
> 73
> Gary K4FMX
> =============
> That is a red herring. Because the frequency ratio is about 10 to one
> is the answer.
> This begs the question as to whether the impedance is enough to care
> about, and cap or inductive, or a series resonance. Such wonderful
> considerations are why we can discuss this matter after over 50 years.
> Wil
> _______________________________________________
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> Amps@contesting.com
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