[AMRadio] Rothman Modulation

Geoff/W5OMR w5omr at w5omr.shacknet.nu
Wed Dec 22 10:24:26 EST 2004

This is a new term, for me.  So, a Googling I went.

Not much information on Rothman Modulation, but there was some.
Perhaps someone else on here can add to this?

73 = Best Regards,

Article: 101889 of rec.radio.amateur.boatanchors
From: Edward Knobloch <alias at nowhere.net>
Subject: Re: Info needed on "Taylor Modulation" from the 50's.
References: <shcin090tfr8ge013ac7b8e9sdifljiav1 at 4ax.com>
Message-ID: <J6bed.360$Ae3.55 at trndny02>
Date: Fri, 22 Oct 2004 17:06:49 GMT

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

and the reply was...


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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