The answer is in the Heath Manual, if I could figure out how to cut
and paste from a pdf file I would have included it.
It's on page 83.
Now if you agree or don't agree that's another thread !!
73, Dick, W1KSZ
> To: lists@subich.com; alexeban@gmail.com; amps@contesting.com
> From: audioguy@charter.net
> Date: Wed, 29 Jul 2009 22:10:39 +0000
> Subject: Re: [Amps] grounding grids
>
> So why did Heath do it then? (Chokes et al)
> Inquiring minds want to know
> 73, --jim
>
>
> Sent from my BlackBerry® wireless device from U.S. Cellular
>
> -----Original Message-----
> From: "Joe Subich, W4TV" <lists@subich.com>
>
> Date: Wed, 29 Jul 2009 17:49:20
> To: 'Alex Eban'<alexeban@gmail.com>; 'Ham-amps'<amps@contesting.com>
> Subject: Re: [Amps] grounding grids
>
>
>
>
> > From an RF point of view, the grid is grounded and well,
>
> The Grid is far from "well grounded." With 220 pF in series,
> the grids are above ground by 25 Ohms (Xc) at 28 MHz and 206
> Ohms (Xc) at 3.5 MHz (the design operating range of the SB-220)
> ignoring the Xl of the long and thin leads on the capacitors
> and the effects (including distributed capacitance and internal
> resonances)) of the RF chokes.
>
> 25 to 200 Ohms is far from "well grounded" and an opportunity
> for oscillation at some frequency. For a more rigorous analysis
> see: http://www.w8ji.com/vhf_stability.htm
>
> Again, placing ANY impedance in the grid portion of a "common
> grid" circuit is an invitation to instability and the impedance
> of all grid connections should be minimized. Eimac's air system
> sockets even include slots to allow the shortest possible strap
> connections from the grids to chassis.
>
> 73,
>
> ... Joe, W4TV
>
>
>
>
>
> > -----Original Message-----
> > From: Alex Eban [mailto:alexeban@gmail.com]
> > Sent: Wednesday, July 29, 2009 1:29 PM
> > To: 'Bill W5WVO'; lists@subich.com; stevengrant98@yahoo.com;
> > 'Ham-amps'
> > Subject: RE: [Amps] grounding grids
> >
> >
> > ...the key to the stability is the capacitors! From an RF
> > point of view, the grid is grounded and well, since
> > capacitors work well at 6 meters.
> > Alex 4Z5KS
> >
> > -----Original Message-----
> > From: amps-bounces@contesting.com
> > [mailto:amps-bounces@contesting.com] On Behalf Of Bill W5WVO
> > Sent: Wednesday, July 29, 2009 7:58 PM
> > To: lists@subich.com; stevengrant98@yahoo.com; 'Ham-amps'
> > Subject: Re: [Amps] grounding grids
> >
> > Joe Subich, W4TV wrote:
> >
> > > While the 3-500Z and other older glass tubes don't have
> > > as much gain as the newer external anode tubes, the
> > > principle is the same. If there is enough gain and the
> > feedback is of
> > > the correct phase the tube will oscillate. Placing any impedance in
> > > the "grounded" grid of a common grid circuit increases -
> > not decreases
> > > - the chances of oscillation.
> >
> > How would you characterize, then, the design of the SB-220,
> > where the 3-500Z
> >
> > grids are grounded through RFCs and bypassed by dsk ceramic
> > caps? Particularly
> > since this particular amplifier has been converted to 6m use,
> > but the grid
> > components are still originals from the HF version.
> >
> > Would this amplifier be more stable with the grid pins
> > directly grounded to
> > chassis?
> >
> > Bill W5WVO
> >
> > >
> > > 73,
> > >
> > > ... Joe, W4TV
> > >
> > >
> > >
> > >> -----Original Message-----
> > >> From: amps-bounces@contesting.com
> > >> [mailto:amps-bounces@contesting.com] On Behalf Of Steven
> > Grant, W4IIV
> > >> Sent: Wednesday, July 29, 2009 10:45 AM
> > >> To: Herzog; Ham-amps; Bill Fuqua
> > >> Subject: Re: [Amps] grounding grids
> > >>
> > >>
> > >> This was used on newer tubes (3-500Z - ect) to raise the
> > resonance of
> > >> the grid to control parasitics. It is not needed for older tubes
> > >>
> > >> STEVEN GRANT W4IIV
> > >>
> > >> --- On Wed, 7/29/09, Bill Fuqua <wlfuqu00@uky.edu> wrote:
> > >>
> > >>
> > >> From: Bill Fuqua <wlfuqu00@uky.edu>
> > >> Subject: Re: [Amps] grounding grids
> > >> To: "Herzog" <herzog@frontiernet.net>, "Ham-amps"
> > >> <amps@contesting.com>
> > >> Date: Wednesday, July 29, 2009, 9:28 AM
> > >>
> > >>
> > >> Maybe to measure individual grid currents?
> > >> That would be the only reason I can think of.
> > >> 73
> > >> Bill wa4lav
> > >>
> > >> At 08:35 PM 7/27/2009 -0400, Herzog wrote:
> > >>> RE: > >Hi.
> > >>>>> This has probable been asked before on this group,but... Is it
> > >>>>> good practice to physically tie the grids to ground via one
> > >>>>> connection,or via low value resistors and decoupling
> > capacitors. I
> > >>>>> was
> > >> going to go for VHF
> > >>>>> practice and go for direct grounding,but would like
> > >> some comments before
> > >>>>> progressing this project.
> > >>>>> 73`s Jon
> > >>>
> > >>> REPLY:
> > >>>
> > >>> I'm curious - what would be the reason for using resistors and
> > >>> decoupling caps?
> > >>>
> > >>> 73, Bill W6WRT
> > >>> ===========================
> > >>> Herzog proffers a reason, to be able to measure the grid current.
> > >>> _______________________________________________
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> > >>> Amps@contesting.com
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> > >>
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> > >>
> > >>
> > >>
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