In a message dated 1/21/05 1:49:18 PM Central Standard Time,
wlfuqu00@uky.edu writes:
For an L you need the capacitance on the high-z side.
*** In this case the tube side would be the high-Z side. It would be the
plate capacitance of the tube itself.
The capacitance
should be from plate to ground
***Plate capacitance IS from plate to ground!
and the L in series with the 50 ohm
load.
***In the case I was describing it is series with the original tank circuit.
***It is basically a 2 stage impedance matching filter. Or you can
consider it a pair of back to back PI networks where the output C of the first
PI
network and the input C of the second PI network are added together as a
single
C value.
Q is the square root of the impedance ratio. You need adjustable L
and C to match on all frequencies.
**Correct in theory but not necessarily in practice!
***But if he only had that tuning problem on the highest frequency, the
solution provided by adding that small amount of inductance may work fine
because
as he switched to lower bands the added inductance would have less and less
effect on the impedance transformation ratio. Thus it would have less effect
on his ability to tune and match impedances to the new lower frequency
settings.
Oddly enough I have seen it used but when I tried it with my 4-1000 I could
not get it to work.
***The only times I have had 'significant' success with it was when the
plate to ground capacitance of the output stage was so high that I needed to
up-convert impedance to get a reasonable Q and reduce the circulating currents
in the tuning circuitry. I doubt that you had that type of a problem with a
single 4-1000.
I will revisit it some time or another. I had hoped to
use a L output on my amp and then follow with switched low pass filters
which could be use with any of my amplifiers but simplify the amp itself.
*** Then I suggest that you find yourself one of those chain driven rotary
inductors like they used to use in the old Henry amplifiers because you will
probably need one.
***Regards,
***Dennis O.
73
Bill wa4lav
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