[Amps] 10 KW CCS ON 6M...USING THE 3CX-6000A7... PART 12

[jim.thom jim.thom@telus.net]

<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

## Did u read my previous note?
" 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

The issue is the anode to grid C is already 34.5 pf...which rises to a
whopping 43-44-45 pf
when tube plugged into the grid ring.  The extra  C is from the proximity
of the lower anode fins to the chassis below em.   We can only get the  C
tune cap so close to the output of the plate block cap assy....like 1".
Any inductance between the plate block cap assy and C1 tune cap will not
harm anything, if fact it will then start the beginning of a L-PI network.

Toss in any stray C from rear or side wall or top lid, or anything else u
can think of, and it just gets worse. Even just 1-2 pf will screw it up.
 I already tried the design, mocked up on a new blank chassis, using just a
conventional PI network, no side walls, no top lid...and virtually zero
length between anode and input to plate block cap assys...and  almost zero
length between output of block cap assy..and C1 tune cap.  Then various
inductor configs for uh between tune and load caps, moving the load cap
each time to minimize lead length.   And both caps mounted vertical.

"works"   BUT tank Q is sky high.(20). That was using a cap with a 5 pf min
C.  Never even seen or heard of a cap with a 2.5 pf min C.  Even with a 2.5
pf min C cap, Q would only reduce to 19.  And still too high.  We said piss
on this, and went to the L-PI network. Ok, now Q is exactly 11... with zero
effort required..and using a cap with a 10 pf min C.

I gave up on PI nets for 15, 10, + 12 m.....and also 6m.  Sure, they
will..'work', but Q is too high, coil gets too hot, narrow bandwidth etc.
The L-PI is easy to design, and real easy to get working correctly.  I
find  5 pf min C caps are extremely rare and hard to find.  The typ caps
have a 10/12 pf min C..and easy to source.