First triode bridge self oscillating converter?
The following US patent from 1925 by Jackson Pressley shows a Super-Heterodyne Frequency conversion circuit with one triode.
The oscillator energy is isolated from the antenna circuit with a cancelling bridge circuit, as was commonly done with FM self oscillating triode converters in the 1950's.
Is this the first known Self-oscillating bridge converter (selbstschwingende additive Mischstufe)?
A later US patent by Maurice Philips adds an RF preamp with Miller capacitance neutralization implemented at the Loop antenna. This neutralization is similar to the Rice method. The Miller neutralization using the loop antenna also serves to cancel any residual Local Oscilator energy that was not completely cancelled by the oscillator bridge.
I became aware of the Pressley patent from a mention in an article about Super heterodyne oscillators of the 1920's by Richard T Ammon in the April 2009 Vol 50 #2 issue of the Antique Wireless Association (AWA) Journal.
Is this Pressley's circuit which was called Autodyne?
To me it looks similar to the Tropadyne principle insofar as both are feeding the RF to a "cold" (center) tap of the oscillator tuning coil.
In ARC, July 2000, p.5, Clyde Fisk is mentioned as the inventor of the Tropadyne. But there are no data whether a patent was filed and when.
Fitch proposed the Tropadyne as an improvement to both the basic Autodyne and the Second Harmonic Autodyne.
These are in US patents 1,667,513 and 1,762,221. These would therefore be in about 1928 and spanned the Philips patents.
Such circuits and the complex refexing employed to minimise the tube count whilst retaining sensitivity, were good examples of inventiveness unlike the "brute force" multi-tube superhets of the subsequent decade!
(Ref J T Bernsley 1937)
The article from ARC (Antique Radio Classified) July 2000, that you mentioned is available on-line at:
The title of the article is "The Mighty Superhet" BY BILL CORKUTT.
This good article covers Bill's personal experience with some superhet designs from the early 1920's in the triode era.
The patents listed in this thread are also freely available with a simple number search from Google-Patents at:
I am an ARC subscriber (also author about superhets there...) since 20 years... and collected all the paper issues. Great periodical, I love it!
I just didn't have the time now to search for patents . Thanks for the hint.
Hello Konrad, good to know about yet another area of your expertise.
I am starting to find the early superhet era quite fascinating, with creative originality.
A quick search turned up this page listing a definition for all the ___dyne names that came up in the tube era. The page is owned by Rainer Steinführ a.k.a. "Wumpus", apparently not a RM member.
In the original German:
For a translation, just paste this URL into Google-Translate.
I looked for your article contribution to Antique Radio Classified ARC at
I found your letter to the editor of ARC at
with the offer of an article for publication,
I would very much like to read that article, and I think the forum audience would too. Can you please direct us the approriate link?
no problem: the article "Early Home-Brew Superheterodynes"
is in ARC vol.19, March 2002, No.3, pp. 9-11.
Unfortunately I cannot find a www link. But pics can be seen of the USA example
and the French one here.
There is something else on the topic in ARC:
- Chris Cuff, The Superhets of the 20s - Part I;
"The Popular Mechanics Superheterodyne Eight",
ARC vol.8, Oct.1991, No.10, pp.8-10
- Chris Cuff, The Superhets of the 20s - Part II;
"The Samson Super-kit",
ARC vol.9, May 1992, No.5, pp.10-12
I love these monsters....