[AMPS] Tuned Input Circuit Q

2 2@vc.net
Tue, 9 Oct 2001 12:09:05 -0700

>> You, Rich, and Eimac like pi networks.
>No, I "like" ANY network that provides a low impedance from 
>cathode to ground for harmonics of the drive frequency at the 
>cathode of the tube.  It doesn't matter what that network is, as long 
>as it bypasses the cathode for harmonics of the plate current 
>waveform and isolates harmonics generated in the tube from the 
//  By omitting the aforementioned four-letter word that begins with "R", 
you might have gotten a less verbose answer. 
>> Creative Electronics, RF Power Products, ETO-Alpha. myself, and others like
>> parallel or T networks. 
>That doesn't make it a good choice! Just look at IMD in reviews of 
>amplifiers (and transmitters), and you will see how little attention 
>people pay to building clean systems.
//  The FCC's Paragraph D says that splatter in a ham-band should not go 
beyond the band edges, so why make ham stuff as clean as possible?  

>While parallel networks are often just as good, T networks are 
>really a very poor choice. They are a system begging for less-than-
>obtainable IMD or efficiency.
>You have two basic flavors of T networks, and while one type is a 
>low-pass and will reduce harmonics appearing back at the exciter 
>none of them do a good job of ensuring that cathode doesn't pump 
>around with harmonic energy.
>If you have to use three components and a DP switch, you might 
>as well do it the most reliable way no matter what you "like". You 
>never know what cable length and exciter someone will use.

//  In other word's, Ameritron/MFJ's expert sorta likes low-pass 
Pi-networks when a Z-transformation is needed -- i.e., the g-g tube's 
cathode isn't 50-ohms.  

>73, Tom W8JI


-  R. L. Measures, 805.386.3734, AG6K, www.vcnet.com/measures.  

FAQ on WWW:               http://www.contesting.com/FAQ/amps
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com