[Amps] .82 ohm

[R.Measures]

On Dec 7, 2004, at 9:17 AM, Colin Lamb wrote:

> Rich said:
>
> "if a g-g amplifier is tuned for max P-out, grid dissipation will 
> always be reasonable"
>
> It seems that statement includes the reasons why a grid meter is 
> desired.  Let us explore one example.  The antenna swr jumps up 
> substantially because a low flying hang glider clips off part of it.  
> The plate amplifier will no longer be tuned for max P-out.  The plate 
> current meter may be anywhere.  We do not know about the output meter, 
> however if we are watching voltage, there may be such a substantial 
> change in impedance that the voltage remains the same even though 
> loading is changed.  In that case, grid current would increase 
> substantially

This would depend on which way the feed Z went.  If the feed Z 
decreased I-grid would decrease unless the C-tune and C-load were 
readjusted.

 >
> and would be the only meter that would indicate the problem.  
> Redundancy of metering is not a bad thing, especially where operators 
> often ignore them.

An SWR meter would do the job.
>
> Even better are flashing leds that indicate excessive grid current, 
> because they are instantaneous.
>
> Another case would be where the plate choke burns out because you are 
> operating on 12 meters.  In that case, no plate current will flow, or 
> if in the cathode, only a small amount.  Hams have been known to keep 
> whistling into the mike trying to figure out what went wrong, 
> increasing their drive, while blowing their grids out.  A grid meter 
> might prevent that.

Choke fires are pretty hard to miss since the smoke plume typically 
causes a stentorian HV flashover to the roof of the RF deck.  .
>
> Besides that, how can a red blooded ham have a meter that does not 
> dance when the amp is in operation.  Sometimes I put extra meters on 
> just to watch them all work.  Some of the great transmitters have 8 
> meters.
>
8 is definitely enough.

> Colin  K7FM
>
> -----Original Message-----
> From: "R.Measures" <r at somis.org>
> Sent: Dec 7, 2004 8:39 AM
> To: kwasny <kwasny at netzero.net>
> Cc: amps at contesting.com
> Subject: Re: RE : [Amps] .82 ohm
>
>
> On Dec 7, 2004, at 7:24 AM, kwasny wrote:
>
>>
>> ----- Original Message -----
>> From: "R.Measures" <r at somis.org>
>> To: "hermans" <on4kj at skynet.be>
>> Cc: <amps at contesting.com>; "'kwasny'" <kwasny at netzero.net>
>> Sent: Monday, December 06, 2004 3:30 PM
>> Subject: Re: RE : [Amps] .82 ohm
>>
>> How would one determine if the grid current is being exceded?
>
>   --  There is no max. grid-I rating on 3-500Zs or 3-400Zs.  The max.
> grid dissipation for a pair is 40w, however, provided that it isn't
> being driven beyond the max anode-I rating of 0.8A, if a g-g amplifier
> is tuned for max P-out, grid dissipation will always be reasonable.
> The reason for this is that diverting more electron flow to the grid
> requires detuning so that less than optimal power out results.  Thus,
> when P-out is max, one can relax.
> -  The type of amplifier that requires a grid-I meter is: Class AB1
> grid-driven, not Class AB2 cathode-driven.
>
>> I have no
>> doubt that is was caused the problem with my SB-220 in the first
>> place. I
>> inadvertently drove it at full output from my exciter (110 to 120
>> watts).
>> That is when the trouble started.
>
> Whenever I tune my SB-220 or TL-922,, I fully drive it to 0.8A because
> I know that if I drive it to less anode current,  RL will decrease and
> I will have a mistune when I drive it to full PEP.
>>
>> Darryl - K5WAS
>>
>>
>> The safest thing to put in place of a kaput grid-current meter shunt
>> (R3) is a jumper wire since the meter can not could not be damaged by
>> another anomaly, and grid-current metering is of no value - either
>> during tune-up or operation.
>>
>> On Dec 6, 2004, at 12:03 PM, hermans wrote:
>>
>>> What about putting 4 x 330E (0.6 W) in //?
>>>
>>> Jos on4kj
>>>
>>> -----Message d'origine-----
>>> De : amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]
>>> De
>>> la part de kwasny
>>> Envoyé : lundi 6 décembre 2004 16:03
>>> À : amps at contesting.com
>>> Objet : [Amps] .82 ohm
>>>
>>> I have been working on my SB-220 which had a parasitic oscillation. I
>>> have installed the parasitic oscillation kit but stilll have not been
>>> able to find a 2 watt .82 ohm resister which blew. Where can I get
>>> that
>>> resister? I live in the Ft Myers area and we have absolutely NO
>>> electronic part stores here. The closeist one is in Sarasota which is
>>> 60
>>> miles away. I would like to get a few of thest resisters by mail if
>>> possible.
>>>
>>> Thanks, Darryl - K5WAS
>>
>> Richard L. Measures, AG6K, 805.386.3734.  www.somis.org
>>
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>>
>>
>>
>
> Richard L. Measures, AG6K, 805.386.3734.  www.somis.org
>
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>
>

Richard L. Measures, AG6K, 805.386.3734.  www.somis.org