[AMRadio] Rothman Modulation

Patrick Jankowiak recycler at swbell.net
Wed Dec 22 19:16:15 EST 2004

I would like to know more, here's all I ever found.


From: StephenTetorka at cs.com
Subject: [AMRadio] AM space

Hello All:

It is my observation that there is a goodly amount of 'open' 
space from 14.3 to 14.35 MHz. most of the time.

Conditions are not favorable as 75...but having ample 'elbow 
room' sure feels good.

Would it be worthwhile to consider an AM gathering location there?

PS: anyone familiar with Rothman AM modulation?

Happy Holidays,

Mike Baker <k7ddmjb at qwset.net> wrote:
Hello to all.
When I was a kid I recall reading something in an old CQ/73/QST
magazine about a modulation method for AM called Tayor 
Modulation.  It was sort of a precursor to controlled carrier and 
used a seperate modulator tube hooked up sort of in parallel to 
the final amp and usually was the same tube type.  There was no 
modulation transformer like in typical class B High level 
modulation schemes.

Hi, Mike

You are thinking of "Rothman Modulation" April 1952 CQ.
(Which I can't find).  If I recall correctly, controlled
carrier screen voltage for the finals was derived from the rf 
output carrier power.  I remember a picture of an outboard box 
with a couple of 6Y6 style tubes (perhaps it was a single 6Y6 and 
a rectifier tube), modulating a pair of 813's.

Ed Knobloch

Article: 101890 of rec.radio.amateur.boatanchors
From: "COLIN LAMB" <k7fm at teleport.com>
References: <shcin090tfr8ge013ac7b8e9sdifljiav1 at 4ax.com> 
<J6bed.360$Ae3.55 at trndny02>
Subject: Re: Info needed on "Taylor Modulation" from the 50's.
Message-ID: <zZbed.4367$KJ6.1794 at newsread1.news.pas.earthlink.net>
Date: Fri, 22 Oct 2004 18:05:19 GMT

Hello Ed:

My wife says I have so much crap I could not possibly find 
anything - but I walked right to the shelf where the April 1952 
CQ magazine was.

You are therefore batting 1 for 3, since you got it right on the 
outboard chassis, but wrong on the 6Y6 style tube.  However, when 
you get to be our age and have forgotten more circuits than the 
younger hams have ever read about, that is not that bad.

Anyway, there were two different circuits shown.  A 100 watt 
mobile modulator using a 6X4 rf rectifier with a 6SN7 modulator 
tube, and a fixed station modulator for up to 1000 watts uisng an 
80 rf rectifier, a 6SL7 speech amp and a 6CD6 modulator tube. 
Since the 6CD6 tube has a plate cap, it does not look like a 6Y6. 
  The 6BQ6 and 6BG6 can also be used.

I have a number of 6CD6 and 6BG6 tubes and never could figure out 
what to do with them.  This is the answer.  Build dozens of 
Rothman modulators.

I think later that year and into 1953, you could buy an 
"efficiency Modulator" using this system.  They claimed 70% 
efficiency, which was much better than the 52% efficiency of high 
level plate modulation.

And my wife thinks I cannot find things.  Ha.

73,  Colin  K7FM


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