Hi Alek...
If your plate choke were absorbing even 100W I believe it would quickly
become hot enough to smoke. Another possibility - maybe - a choke impedance
consisting of a low value of effective series reactance and also relatively
low effective series resistance (i.e., near a high Q series resonance?) at
your op freq could CONCEIVABLY make it impossible to tune the tank close
enough to get significant output.
This is pure speculation; I don't recall having seen such a situation,
where the choke screwed up tuning but didn't overheat. But it seems
conceivable. Ian? Tom? John? Carl? Anybody experienced this?
73, Dick
-----Original Message-----
From: Alek Petkovic [SMTP:vk6apk@faroc.com.au]
Sent: Monday, June 01, 1998 6:49 AM
To: amps@contesting.com
Subject: [AMPS] No 24 MHz
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. 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!
Do you think that the plate choke is sucking all the rf out on 24MHz? If
so, was there a successful conclusion to this topic when it was running?
Should I wind a different choke and try that?
Your thoughts would be appreciated.
73 de Alek, VK6APK.
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