The AM Forum

This book was recently given to me by Bob, W3NE.  It's another one of Frank Jones great works.  It has 86 pages and is quite comprehensive.  Like the ARRL handbooks, some great Ad's appear in the back section.  Hammarlund was touting 310 degree bandspread for the newly introduced HQ-120.  Bud introduced the model XC-25 kit which was a 25W output rig covering all bands from 160 thru 10 meters.  Frank Jones advertised his HM-170 transmitter which ran 75W on AM and 100W on CW.  Of coarse it was cathode modulated!  I wonder how many HM-170's are still around?

Joe, W3GMS   

   I would sure like to find a copy of that Jones work for my radio
   book shelf.   Always was a fan of that method of generating AM.

   As I recall one of the transformer manufactures had a cathode
   mod transformer in their product line.

    Joe, would you consider a full scan of it?  I bet there are others
    out there who would appreciate it as well...

Joe,

I always thought the Jones books were better than the league books as far as contruction of equipment was concerned. While the league books focused mainly on the rules, operating procedure, and getting someone licensed; the Jones books showed you how to build a rig and get on the air.
Jones sold off many of his construction projects to hams, usually in the classified section of Radio magazine. The Jones tx my OM and I have is a perfect example. The man who bought it saved the original magazine which had the ad in the back. Also saved were all the follow up correspondance between him and F. Jones. In my opinion, that is worth more than the rig. I'll bet the rig in that book was a one of a kind or only a handful were ever made, log in scrap heap.

Ralph,

Stancor made a cathode modulated rig with an 807 modulated by a 6v6.

Mike

As I recall, some of the multi-match modulation transformers instruction sheets included tap connections for use with cathode modulators.

That was real cathode modulation.  The pseudo-cathode modulation you often see in more recently published articles, consisting of a low plate resistance audio power tube in series with the cathode of the final amplifier stage, is not really cathode modulation; it is a form of control grid modulation.  The tube acts as a variable cathode resistor, so the final is grid modulated via variable cathode bias.

Real cathode modulation uses a split transformer winding in a configuration that applies a combination of grid bias and plate modulation.  Depending on the amount of audio power available, adjusting the ratio of grid to plate modulation allows the available audio power to fully modulate the final to 100%.  The efficiency is higher than  with pure grid modulation, but lower than with pure plate modulation.  The actual efficiency is a function of the ratio of grid to plate modulation.

Near-100% plate modulation with as small amount of grid modulation using the  cathode modulation circuit should improve modulation linearity over pure plate modulation, basically working the same as applying a small percentage of modulation to the driver stage along with the plate modulated final, as for example, the circuit in the Gates BC-1T and series that follow.

I have several of the RADIO magazines with articles written by Frank Jones or Ray Dawley concerning cathode modulation.

Kenyon also made cathode mod transformers.

See catalog page attached.

If this book isn't still under copyright, it would be great if someone could scan it.

Dave

Frank C. Jones, was considered to be the guru of all things cathode modulation!


Mikey, Stancor also made a cathode modulated rig using an 812 for a final, IIRC it used a pair of 6L6s for modders. Derb used to have one, pretty kool little rig!

I also have this book in my Frank Jones collection, along with various handbooks from the 1930's and 1940's.  It covers the technical aspects of cathode modulation with very good detail. I like the back cover which provides info on cathode modulating a pair of 810's.

I have a CM-16 cathode modulation transformer that I found at a hamfest years ago. Maybe I'll get around to using it in some future transmitter project.  It's on my list.

73 Jerry W1ZB

A good example of holding on to a rare vintage part you happened to find.  If you had thrown it out after a year or so because you didn't have any immediate use for it, you would likely never find another one, and there would be one less of those hard-to-find transformers left on the planet.

Mike,

I totally agree about Frank Jones and his great contributions to our hobby.  Each of the various handbook have there place, but he was very focused on the practical aspects of building.  Like Jerry, I have several of his Handbooks as well.  I had heard that before about him selling the rigs he built and in some cases they were the prototypes.  That's great that you and your Dad have an example of his work along with all the documentation that supports it.  What a find! 

It would be nice to learn more about Frank Jones himself.  The history behind these guys is usually pretty interesting.   

Joe, W3GMS   

The two pre-war gurus:

Frank Jones;

http://www.vomarc.org/history.html


George Grammer;

http://www.oldqslcards.com/3AIH.pdf

73DG

That Stancor rig used a pair of 6V6s as modulators. I had it in warm storage for Derb over several years.

Frank Jones was the man.

Yes, George Grammer was another great contributor.  We can't forget James Millen and all the contributions he made while at National during the 30's and then his own company after he left National.  Ross Hull was another great contributor.  The list goes on and on I am sure.  Those mentioned shared there knowledge very willingly in print and Millen in particular went on to commercial success with his legendary products.   

Joe, W3GMS