>Hi all,
> I was playing around with my 2 x 3-500Z Homebrew amp and doing a
>few refinements to the plate tank circuit coil taps. I thought I would look
>at getting 24 MHz going. It's the one band that has never worked on this amp.
>
> I had no joy at all and so I think it may be a resonance at 24.9 MHz in
>the plate choke. I know that there was a quite extensive discussion on this
>reflector about plate chokes not too long ago. I didn't think it affected
>any of my gear at the time so I never involved myself in the subject too
>much.
>
>I'll try to describe the symptoms. See what you think.
>
>I have separate taps on the Pi coil for 21, 24 and 28MHz.
>
>On the 21 and 28MHz switch positions, I can apply some 24.9 MHz rf drive
>and I get an output shown on the power meter. If I do the same on the 24MHz
>position, I get plate current and grid current but absolutely ZERO output.
>
>I always suspected a poor joint or open bandswitch contact but I found
>everything ok there. I proved it by switching to the 24 MHz position and
>then applying a small amount of drive on both 21 and 28MHz. I got an output
>on both occasions.
>
>I have not tried taking it out and measuring the self resonance with the
>dip meter as yet.
[please see note below]
>I will try that next weekend if I don't drink too much beer.
>
>The choke is homebrew and stagger wound, (No I didn't wind it while I was
>staggering around drunk) supposedly to break up any possible resonances. Ha!
Perhaps the guy who came up with the nutty idea was staggering?
Apparently, he never took the time to check out his idea with a dipmeter.
>
>Do you think that the plate choke is sucking all the rf out on 24MHz?
If it was, it would ignite.
>
>If so, was there a successful conclusion to this topic when it was running?
>Should I wind a different choke and try that?
>
If there are no choke resonances within 5% or so of an operating freq.,
there should be no choke fires, Alek. If you have a problematic
resonance, removing turns is the best way to deal with the problem.
[note: HV-RFC's should be checked for resonances when they installed in
the amp.].
>Your thoughts would be appreciated.
>
>73 de Alek, VK6APK.
>
>--
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Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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