[Amps] grounding grids

[Gary Schafer]

Joe,

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


> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
> Behalf Of Joe Subich, W4TV
> Sent: Friday, July 31, 2009 12:51 AM
> To: 'Jack Shirley'; amps at contesting.com
> Subject: Re: [Amps] grounding grids
> 
> 
> 
> >
> > The answer is:
> >
> > to provide -2db negative feedback. This was done to match the
> > output power of the TR-3 and TR-4.
> 
> At what frequency since the impedance between the grid and
> common (ground) changes by a factor of nearly 10:1 between
> 3.5 MHz and 29.7 MHz?  What other steps were taken to hold
> the -2dB feedback constant across the operating range?
> 
> 73,
> 
>    ... Joe, W4TV
> 
> 
> 
> > -----Original Message-----
> > From: amps-bounces at contesting.com
> > [mailto:amps-bounces at contesting.com] On Behalf Of Jack Shirley
> > Sent: Thursday, July 30, 2009 11:00 PM
> > To: Thomas Carlsson
> > Cc: amps at contesting.com
> > Subject: Re: [Amps] grounding grids
> >
> >
> > The answer is:
> >
> > to provide -2db negative feedback. This was done to match the
> > output power of the TR-3 and TR-4.
> >
> > Also of note; it was the first 3-400/500 amp to have tuned
> > input circuits,
> >
> > The output circuit was designed to match a 2 : 1 SWR at all
> > impedance's and phase angles.
> >
> > He also designed the MN-2000 which will match a 5 : 1 SWR at
> > all impedance's/phase angles.
> >
> > At one time they were getting L-4s in for service which had
> > the pi wound grid chokes where the windings were " slammed
> > together" .. This was from plasma arcs inside the tube going
> > thru the grid. He called EIMAC about this  and they said when
> > the 3-500z are being  vacuumed sealed, they put high voltage
> > on all the terminals to burn off the metal whiskers which
> > form during the process. Eimac said " guess we will have to
> > let them burn off longer " . After that the problem went away.
> >
> > The cost of a 3-500 was 24.50 then.
> >
> > Any other questions?
> >
> > 73 Jack N8DX
> >
> > On Thu, Jul 30, 2009 at 10:00 PM, Thomas Carlsson
> > <thomascarl at gmail.com>wrote:
> >
> > > Interesting addition: LK-500 and its brothers have Grids direct to
> > > Ground, no components. Cathode resistor only 0.15ohm/3W. SB220 and
> > > L4(B) both 1ohm in cathode and they have the same grid
> > components, on
> > > schematics I have the RFC and C's are copies of each other. 73,
> > > Thomas, PY2ZXU/SM0CXU
> > >
> > >
> > > On Thu, Jul 30, 2009 at 8:25 PM, Jack Shirley <jcshirle at gmail.com>
> > > wrote:
> > >
> > >> I looked at the various 3-400 and 3-500 circuits in the
> > Eimac Amateur
> > >> Service Newsletters and did not find this mentioned anywhere.
> > >>
> > >> If the SB-220 and L4 use the same grid circuit, I could ask the
> > >> engineer who designed the Drake L-4 as I know him personally.  Any
> > >> interest?
> > >>
> > >> 73  Jack N8DX
> > >>  On Thu, Jul 30, 2009 at 6:48 PM, Ward Silver <hwardsil at gmail.com>
> > >> wrote:
> > >>
> > >> > > perhaps somebody with an SB-220 and a spectrum
> > analyzer needs to
> > >> > > do an IMD profile using each grid circuit and SEE which one
> > >> > > produces the cleaner output.
> > >> >
> > >> > What?!  And ruin a perfectly good thread?
> > >> >
> > >> > 73, Ward N0AX
> > >> >
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> > >
> > >
> > >
> > > --
> > > Thomas, PY2ZXU/SM0CXU
> > > Member of the PW2D Team
> > >
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