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@somis.org>
Sent: Dec 7, 2004 8:39 AM
To: kwasny <kwasny@netzero.net>
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.
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@contesting.com [mailto:amps-bounces@contesting.com]
De
la part de kwasny
Envoyé : lundi 6 décembre 2004 16:03
À : amps@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
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