[Amps] Question for the tetrode experts

[Vic K2VCO]

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 at 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 at 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/