On 14 Mar 2023 at 5:17, Mack McCormick wrote:

>
> Ken,
>
> Thank you. I  made a typo in my original posting. I am using 2000pf not 4000pf.
>
> Mack
> W4AX

Oh. OK.

Second question: are you sure your 813 is not weak or worn out? As I read it from various
documents I have here on the ART-13, output should be around 100 watts.

You are getting 60 even with SWR at 1:1. That almost perfect SWR means to me that your
impedance-matching must be close to perfect.

And THAT sounds to me like a weak tube.

At this point, I sincerely doubt that your problem has anything to do with tuning. Yours sounds
pretty close to perfect.

Lastly, how is your screen voltage? Low screen voltage to the final can also cause low power
output.

But you know that.

I think that if I had the same symptoms you are experiencing, I would, at least temporarily,
jack up the screen voltage to see what that does. The 813 can use up to 1100 VDC screen
voltage for SOME services. If increasing the screen voltage significantly increases power
output, then the tube is weak.

I am assuming you are using an AC supply with 28 VDC, 1150 VDC and 400 VDC outputs.
Are you certain your power supply is up to snuff?

A weak driver tube could also cause your symtoms, but that would show up with low grid
current.

Ken W7EKB