[Milsurplus] Suggested tuning for ART-13 into a 50 ohm antenna on 75M?

[Mack McCormick]

Ken,

These are all excellent thoughts and I too have arrived at the same
conclusion that the probable cause is a weak 813. I have others to test.

The PS is stiff with low ripple. I completely rebuilt it for my friend.
1100 VDC, 400 VDC, and 27.5 VDC. All very stiff and pure.

Let me swap out a couple of 813's and I'll report the results back here.

Thanks again/

73,

Mack
W4AX
https://www.qrz.com/db/w4ax


On Tue, Mar 14, 2023 at 2:13 PM Kenneth G. Gordon <kgordon2006 at frontier.com>
wrote:

> 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
>
>
>
>
>
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