[Amps] grounding grids

Wed Jul 29 17:20:13 PDT 2009

Oh the torture... For usn's that don't have the SB-220 manual, anyway.

Or, come to think of it... do I? This might require a romp through the 
stacks. That usually turns something up, although rarely what I started 
off looking for. ;-)

73,
Jim, N7CXI

RICHARD SOLOMON wrote:
> 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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