Grids are typically not damaged by too much current at the frequency of
operation since tuning for max electrons out does not leave enough
electrons to damage the grid. Instead, grids are usually damaged by
parasites at a frequency where they can not pass through the low-pass
Pi-net tank circuit.
On Feb 9, 2005, at 10:21 PM, Bob Maser wrote:
Full smoke out the door with an eye on the grids is the best way to
tune a GG amp. KISS in full force.
Bob
----- Original Message ----- From: "Rob & Terri Sherwood"
<rob@sherweng.com>
To: "R.Measures" <r@somis.org>; "Donald Kessler" <ki6sz@earthlink.net>
Cc: "amps-contesting.com" <amps@contesting.com>
Sent: Wednesday, February 09, 2005 10:20 PM
Subject: Re: [Amps] Two quick loading questions
I have always been puzzled by the "maximum smoke" tuning
recommendations of some amps, AL-80A or B, for example.
A single 3-500Z in linear service is rated at 400 mA plate current.
(350 mA in class C).
When I used to run a Measures/Kessler modified TL-922A (pair of
tubes), I tuned it as follows:
800 mA on the plate and 150 mA on the grid for SSB. If I was running
CW, I tuned it for 200 mA on the grid.
It was very easy to adjust the plate tuning for a grid current peak,
as opposed to trying to see a broad plate current dip.
When tuned for the 800/150 mA conditions, the amp was very linear at
800 mA, and would saturate at something approaching 900 mA.
I always monitor my amps with a Tektronix scope, and set the RF
envelope at 6 divisions at the above plate/grid current conditions.
With a modest amount of speech processing to control the peaks from
the exciter, it is easy to see the linear flattop a bit above the 6
scope divisions.
Set the drive on the exciter to peak the amp at 6 divisions, and I am
completely confident I have a clean signal.
Without a scope, it is difficult to know how hard to drive the amp.
The ballistics of analog meters is all over the map. My Alpha 76PA
was very different from my TL-922A meters. My present Alpha 99 and 89
amps, even with LED metering, are not peak reading devices. In these
two Alpha examples, if the power output is set for 1500 watts key
down, the LED meters read about 800 watts on voice peaks.
R.Measures wrote:
Tuning for max P-out with max-drive is more important than looking
for a dip.
On Feb 9, 2005, at 12:39 PM, George KB2Z wrote:
I'm sure I'm not the first to ask. I have searched in the archives
and did not find a solid answer. I apologize up front and am not
trying to waste anyones time. The directions from different
manufacturers dont seem to answer one way.
As I read the loading instructions for gg hf amps, (2x3-500) they
should be fully loaded at full power then the loading increased 5
to 10% to lower the Ig and help stabilize the output. This seems to
be where it gets confusing for me.
1) After increasing the loading 5 to 10%, should the plate be
re-dipped?
2) If drive is reduced from 100 to 50W, should the plate be
re-dipped.
Thanks in advance, George KB2Z
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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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