[Boatanchors] Resonant Choke Filters (more)

[Richard Knoppow]

----- Original Message ----- 
From: "Dennis DuVall" <duvallddennis at gmail.com>
To: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
Cc: "Boat Anchors" <boatanchors at mailman.qth.net>
Sent: Tuesday, January 06, 2015 12:35 PM
Subject: Re: [Boatanchors] Resonant Choke Filters (more)


Richard,

Terman’s "Radio Engineering," 1937 Edition also includes a 
brief reference to “Tuning one of the series inductances  in 
a multi-section filter to parallel resonance….”  Also 
briefly discusses tapped choke arrangements for hum 
reduction.

Interest in these techniques goes way back apparently. A 
consequence of the high cost of filter capacity back in 
those times maybe?

Dennis D.  W7QHO
Glendale, CA

******************

     I found some discussion in the 1937 edition of Terman, 
on p.499. He shows three arrangements of tuned filters, the 
first having a capacitor across the first choke. However, in 
the text he talks about reducing ripple at a particular 
frequency and not about regulation. Is this different from 
what you saw, if so please give me a page number. Terman 
does not show these filters in the third (1947) edition.
     I also found the illustration in the third (1941) 
edition of the Radiotron. Its shown as "Fig.8" with no 
reference at all in the text but the cut line says the first 
choke is resonated at the fundamental ripple frequency.
     I can't find my 11th edition of the "Radio Handbook" in 
a box somewhere but I think is on line.  I do have a ninth 
edition (1942) which has probably the same information in 
it. The circuit is shown on p.310 as Figure.6  The caption 
is much the same as the one in the Radiotron indicating the 
choke and capacitor is made resonant at the fundamental 
ripple frequency with the warning that while the circuit 
give high attenuation of this frequency it passes more of 
the higher harmonics than a conventional filter and should 
be used with a second choke and condenser. Both Terman and 
the Radio Handbook have a brief discussion of "swinging 
chokes".  These accomplish something like the resonant choke 
in improving regulation. At one time every manufacturer of 
fairly large transformers and chokes offered swinging chokes 
appropriate for ham transmitters. The discussion in the 
Collins book I cited earlier is the only one that discusses 
the use of a resonant choke to improve regulation.
    Note that the "swinging" effect of the swinging choke 
exists in all chokes but to a smaller extent because of the 
larger air gap.
    I am sure the resonant choke has been used in other than 
Collins equipment, if anyone can cite examples I would be 
glad to know. For that matter, if anyone knows of a more 
thorough discussion of the use of resonant filters for 
regulation I would be glad of citations.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com