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

[B. Smith]

Be very careful when extracting the 813 from its socket, the tube socket 
connections are very fragile and break loose from the ceramic.
k4che

On 3/14/2023 6:02 PM, Mack McCormick wrote:
> 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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