[Amps] High C out

[Dennis12Amplify at aol.com]

In a message dated 1/21/05 1:49:18 PM Central Standard Time,  
wlfuqu00 at 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