Gerald,
I have only tested so far on 40 meters. There are no fixed capacitors in the tank on this
band...but there is a ferrite choke across the output. I'll check to see if the choke is
heating.
I didn't notice a big change in plate current -- I will check this also.
On 11/7/2013 4:46 PM, TexasRF@aol.com wrote:
Vic, what frequency? Does the plate current drift?
Screen current is extremely sensitive to the degree of loading adjustments.
Could it be
that there is a capacitor on the output side of the plate tuning circuit that
is heating
due to rf and changing value?
Does the amplifier act the way you described on all bands?
73,
Gerald K5GW
In a message dated 11/7/2013 5:16:12 P.M. Central Standard Time,
k2vco.vic@gmail.com writes:
I've finally applied full drive to my 4CX1000A amplifier. Here is what
I'm
seeing:
I have tried two tubes, both pulls. In one case I can run about 1kW
out, and
with the other, maybe 1200. What happens when I try to push past this
point
is this: when I hold the key down for 10 seconds or so, the screen
current
starts to drop, then goes negative, and when it hits -35 mA the screen
trip
circuit kicks in. I haven't seen even a flicker of grid current.
The screen circuit is well-regulated at 325v, so this isn't case of
runaway
caused by increasing voltage. What it seems like to me is that the
screen is
heating up and the secondary emission is rapidly increasing. Screen
current
before this happens is reasonable, 20-25 mA, so I am not exceeding its
rating.
I have a couple more tubes to try, but I have a bad feeling that I am
going
to end up buying a new tube if I want 1500 watts from this.
Do the experts think my diagnosis is correct?
--
Vic, K2VCO
Fresno CA
[1]http://www.qsl.net/k2vco/
References
1. http://www.qsl.net/k2vco/
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--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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