Hi Luca, (please include your call sign in your postings)
You asked:
"Hello All
I am a new comer this mailing list ,
I would like to know : How to figure the correct inductance value of HV
PLATE CHOKE , there is a relation whit the PLATE INDUCTOR value ?"
Many thanks in advance
73 Luca
First, there is no direct relationship between the plate inductor's
value and the plate choke's value other than incidental reasons (such as
tank circuit current flow, etc., determines the gauge of the choke's
winding).
You didn't specify the ham bands you're interested in, but the situation
is as follows, all according to my own experiences and studies:
The choke's inductance value per se actually is of secondary importance.
It is the self-parallel-resonances of the choke's windings which are
able to present extremely high effective impedances to the tank circuit.
Intermingled with these desirable parallel resonances are destructive
series resonance modes. These must be avoided for use in any ham band
you want to operate on. They cause hot spots--literally high
temperatures--to develop in portions of the choke's windings, due to
high circulating currents in those portions. Moreover, the frequencies
of all these resonances are affected by the proximity to surrounding
objects, mainly the tank enclosure walls.
So, it usually gets down to experimentation, trial and error and past
design successes. Many choke construction articles have been published
in QST, etc., over the years. I will give you details now of my own
perfected design. I use it from 160M through 10M. The choke form
(teflon, etc.) is 1-inch diameter. The wire gauge is #24 enamel/cotton.
The cotton looks so good, and coil dope soaks right in! The over-all
winding length, end to end, is 4-inches. But the winding is in 3
segments or sections, each separated by a full 1/4-inch.
The windings are in progressively shorter lengths, with the longest at
the "bottom" (because it 'looks right' that way!). This choke handles
1500 watts in common styles of ham amp designs.
Remember, it is not easy. (In JFK's moon landing speech, he said, "We do
this because it's hard"). I own a commercial amp now in which the choke
developed a hot spot when used on 17M. I redesigned it. Alpha amps
resorted to using a band-switched plate choke in some models, because of
the difficulty involved in covering many ham bands with a single choke.
Hope this helps some. I don't think there is an actual, practical
formula to accomplish this job.
Good luck and 73,
Roy K6XK
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