It seems quite unlikely that 120 watts would blow the .82 ohm shunt. Oter
forces were at work (Parasitics likely). I often looked at the grid current
but never actually used the reading for anything. Its the readings on the
plate side that make the difference. The Grid current is what it is. Maybe
it could be useful in the one time tuning of the input circuit but even then
one can look at the output. But when that .82 goes, it can take out the
meter. Short is a good idea, and remove the short if you ever need to
monitor grid current, assuming you put another .82 in there. Mine is blown,
meter survived. Replacing it with wire! --Mike, WV2ZOW
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
Behalf Of R.Measures
Sent: Tuesday, December 07, 2004 11:39 AM
To: kwasny
Cc: amps@contesting.com
Subject: Re: RE : [Amps] .82 ohm
On Dec 7, 2004, at 7:24 AM, kwasny wrote:
>
> ----- Original Message -----
> From: "R.Measures" <r@somis.org>
> To: "hermans" <on4kj@skynet.be>
> Cc: <amps@contesting.com>; "'kwasny'" <kwasny@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.
>
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