[Amps] grounding grids

RICHARD SOLOMON w1ksz at q.com
Wed Jul 29 15:54:01 PDT 2009


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 at subich.com; alexeban at gmail.com; amps at contesting.com
> From: audioguy at 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 at subich.com>
> 
> Date: Wed, 29 Jul 2009 17:49:20 
> To: 'Alex Eban'<alexeban at gmail.com>; 'Ham-amps'<amps at 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 at gmail.com] 
> > Sent: Wednesday, July 29, 2009 1:29 PM
> > To: 'Bill W5WVO'; lists at subich.com; stevengrant98 at 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 at contesting.com 
> > [mailto:amps-bounces at contesting.com] On Behalf Of Bill W5WVO
> > Sent: Wednesday, July 29, 2009 7:58 PM
> > To: lists at subich.com; stevengrant98 at 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 at contesting.com 
> > >> [mailto:amps-bounces at 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 at uky.edu> wrote:
> > >>
> > >>
> > >> From: Bill Fuqua <wlfuqu00 at uky.edu>
> > >> Subject: Re: [Amps] grounding grids
> > >> To: "Herzog" <herzog at frontiernet.net>, "Ham-amps" 
> > >> <amps at 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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> > >>
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