I know the BBC video on Youtube.
A Q of 22.5 or 20 is not necessary unless the lead length to the tune cap is
too long and stray C too high.
Here I would use a small vacuum variable with minimum C of 2-3pf, mounted
for minimum stray C vertically and close to the tube.
Then a Q of 15 is possible with a simple Pi, L= 330nH, C2 250pf type vac C.
L wound with 1" or less wide copper strap of course, works well even on 2m.
Fine tuning is not required, only when tune C is omitted.
An L-Pi circuit is always possible as well.
73
Peter, DJ7WW
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of jim.thom
jim.thom@telus.net
Sent: Freitag, 2. Dezember 2022 17:32
To: amps@contesting.com
Subject: Re: [Amps] 10 KW CCS ON 6M...USING THE 3CX-6000A7... PART 12
<With smaller vacuum caps, closer to the grid and only 2" separation between
<them, Q could be much lower and more L for a proper coil might be used.
<73
<Peter
## it still won't work with a vac tune cap with a minimum of 5 pf. (51 mhz)
Q= 21.5
C1= 6.9 pf
L= .22 uh
C2 = 237 pf
1.125" OD copper tubing would still be required. Trying to wind a .22 uh
coil
would be an absolute bitch, and no way to easily tweak it's value.
Circulating current through the coil would be slightly less, but still sky
high, at a whopping 71 amps. A 2" wide strap coil would work, and far
easier to wind, but a bitch to fine tune. You don't get the 'proximity
effect'
with strap coils, since it's like 2 x knife edges facing each other. Strap
coils work good on 12 /10 m.
Ok, let's say you had a magical cap that went down to ZERO pf.
Q-20
C1 = 3.2 pf
L = .23 uh
C2 = 219.6 pf
To be practical, using a vac cap with a min of 5 pf, a Q = 22.5
would have to be used. 5 pf min C vac caps are NOT easy to locate. The 10
pf
min C vac caps are readily available..but then u are stuck with a Q=24-25.
Why use a Q = 22.5 when a Q=12 can be used, just by the addition of the
2nd inductor.
The beauty of the semi circle inductors is.... their length can easily
be tweaked shorter / longer. Shortening is dead simple, one end undone,
1/4"
cut off, then repunched with the ropey whitney hand punch, then
re-terminated.
On one of the 100kw AM SW broadcast pa's in the UK..on u-tube, they used the
same idea, but heavy tubing. They used lock down quick release latches at
each end, to quickly swap inductor's. The U shaped inductors were used on
15 mhz and higher freqs. Tubing coils were used on all lower freqs.
Jim VE7RF
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