[Amps] grounding grids

[Bill W5WVO]

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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