[Amps] Pi-L network

zl1aih at ihug.co.nz zl1aih at ihug.co.nz
Thu Mar 29 14:01:51 EST 2007


Tom said:
>It's pretty tough and very expensive to obtain the perceived 
harmonic advantages of a pi-L in the real world of 
multi-band amps. It's much cheaper to do it other ways.<
So why did so many professional continuous coverage QRO amps (7.5kW
and up) go to the trouble of a pi-L then?
I know of at least 4 different manufacturers who did so....
73
Peter W6/G3RZP this week>

I'm working on a JRC-510 transmitter - 1.6 to 30mHz continuous, 5kW out, passive 
grid-driven AB1 tetrode.
It uses a Pi-L network (switched fixed capacitors, roller inductors, auto-tune) - the 
manual states >50dB harmonic/spurious suppression.

>Tom said:    Do you partition or shield the L coil from the main tank 
coil and tube leads??>

The JRC-510 has a vertical partition between the tube and Pi section, and the L 
section - very serious shielding.

Another amplifier here, Sunair GL-1900 -1.6 to 30mHz continuous, 1 kW out 
passive grid-driven AB1 tetrode - Pi-L network (vacuum C, switched L, vacuum C, 
roller L, auto-tune) also has a shield between the tube/Pi inductor/capacitor section 
and L2 and C2.

I assume that the shielding was to eliminate any unwanted coupling between the 
two L networks.  

73, Ken ZL1AIH





 


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