[Amps] Question for the tetrode experts

[Jim W7RY]

What band?  Are you using padder capacitors on the loading cap?

73
Jim W7RY

On 11/7/2013 3:14 PM, Vic K2VCO wrote:
>     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?