[Milsurplus] [MMRCG] NAVY MAK and HY1269 part two!

[Robert Nickels]

On 5/24/2019 2:54 PM, Ray Fantini wrote:
> I will be searching for the mythical Heising Modulation Reactor. 
> Anyone got any suggestions or ideas?

It's not too mythical, Ray, WRL used Heising modulation in all the Globe 
Scouts because it would save a bit of money to use one 6L6 in a 
single-ended modulator with a simple choke vs a pair and a more 
expensive mod transformer.    No reason it can't be scaled up but 
usually isn't in ham gear at least because the cost advantage goes away 
above about 50 watts or so.

Heising modulation draws a constant-current from the power supply, 
essentially you're just swapping it between the modulator tube and the 
PA tube - when the modulator tube is "on" it draws current away from the 
RF stage, and when it's off the RF stage current rises.   Brilliant - 
but that's pretty much how Ray Heising rolled - he had over 100 patents 
including the Class C RF amplifier as well.

The Heising choke has to be able to pass the DC current and it needs to 
have enough inductance, which is where knowing the value of the original 
inductor would make things easy.    But it's not rocket science - the 
worst case is you won't have sufficient modulation.    When I was 
building a small AM transmitter I found this article in 73 Magazine to 
be the most helpful because it reduces the selection process to a single 
chart:

https://www.americanradiohistory.com/hd2/IDX-Short-Wave/archive-73-idx/idx/60s/73-magazine-02-february-1962-OCR-Page-0030.pdf#search=%22heising%22

It's easy to see that you'll be looking for a choke in the 5-10 Hy range 
that's capable of several hundred milliamps, a much easier thing to find 
than, say, an ART-13 plate transformer (I'm looking!)   Incidentally, 
the author is Jim Tonne, whose name is familiar to anyone who uses the 
popular "Elsie" filter design software, or his Class E design tool.   
He's still around and still doing good technical work.   W8JI also has 
written a lot about Heising modulation, just google it.

Hope this helps - the schematic was too tiny to make out the details, 
tube types, etc, but if you can find a suitable choke you should be in 
business.   Neat rig!

73, Bob W9RAN