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.
Does anyone know/recall where I can get printed information about this
method and its application or why it was not more activly used?

Thnx in advance... Mike Baker K7DD

Mike Baker 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.
snip

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.

73,
Ed Knobloch

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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[quote=COLIN LAMB]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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Hello Colin,
Your call sounds very familar to me. I think we may have either worked before or exchanged information. Anyway, I couldn't help but respond to your comments about "Rothman" modulation. A little while ago I acquired an original "MarMax" Rothman modulator # KW52 that is supposed to modulated a full killowatt final. It's even in it's original box from Harrison Radio in NYC. Fortunately it came with full documentation which differes somewhat from the article in the January 1952 edition of QST. I'm probably going to use it with a pair of 813's or 4-250A's. What I find interesting is that it's connected in series with the screen circut and takes the place of screen B+ in the supply, and uses a single #80 tube to be inductively coupled to the tank circut, though they recommend hardwiring it to the chassis near the swinging link. I plan on trying it out to see how well, and "if" it works.

Best Regards,
Joe Cro N3IBX