Re: LF: RE: LPF for a valve based (tube based) LF amp?

["Dr. Wolf Ostwald" <df2py@t-online.de>]

Hi Chris and Clemens,
surely a Pi-circuit provides a much greater selectivity than an ordinary 
push-pull amp by itself. Which resembles a frequency multiplier.
If one does not need many bands to cater to, a so called Pi-L circuit 
does an extra 10db  attenuation of harmonics on the average. it does 
consists of a series L with output of the traditional Pi-circuit forming 
an extra selctive component with the output C , which is to ground.
All commercial RF amps by Collins Radio Corp. had Pi-L outputs. A bit 
tricky to adjust on multi band amps, but on a monoband amp its just a 
fixed inductivity.
Needles to say that an outboard 5-7-or even 9 pole Tchebycheff filter 
does much better.
I use a 3 and a 5 pole in series. Just as it was developed.
And here working on the tube amp as well.

73 de wolf  df2py