[Amps] .82 ohm

[Colin Lamb]

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 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.  

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.  

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.

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
>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
>

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

_______________________________________________
Amps mailing list
Amps at contesting.com
http://lists.contesting.com/mailman/listinfo/amps