[AMRadio] Re: AM Transmitter Advice??


Bob Deuel k2glo at jkasystems.com
Fri Feb 17 14:09:31 EST 2006


To Jim, John and all:

Jim: The URL you listed is a great site for information on the H&K type 5.
It is quite true that the H&K type 5 never went much beyond the prototype
stage and I have one of those "rare little puppies" in my collection.
However, the larger transmitting gridless Gammatrons were used extensively
in the west coast based Globe Wireless communication system built by H&K.
The complete H&K gridless Gammatron story is about a 30-page article named
"Defiance in the West, The Heintz and Kaufman Story" that was published in
the "AWA Review", Volume X, 1996. It includes pictures of all the different
gridless Gammatrons.

John: The 6AX5GT and some Raytheon 6X5WGT's have the proper plate-cathode
construction that makes them candidates for gridless Gammatron
experimentation. I can not take credit for the initial idea of using the
6AX5GT. Reed Fisher, W2CQH, first introduced the use of the 6AX5GT as an
experimental gridless Gammatron substitute in an article that appeared in
the April, 2004 issue of the "Tube Collector". I refer to both his work and
the above mentioned "AWA Review" article in my article that appears in the
February, 2006 "Tube Collector". Using the above information, I further
refined the 6AX5GT Gammatron operating conditions and developed the AM
transmitter circuit. My article documents my experimental findings and
includes the AM transmitter schematic.

In a nutshell and just enough to peak your interest into pursuing the
articles for all the details, I offer the brief description of operation:

One must reduce the heater voltage of the 6AX5GT to a point the there is a
limited flow of electrons between cathode and one of the two plates that has
been selected to act as the anode. About 15 ma. appears to be optimum in my
circuits with 75 volts on the anode. The second plate is then used as the
Gamma or control plate which is synonymous with the grid connection in a
triode circuit. Control potentials imposed on the designated Gamma plate
diverts some of the cathode to anode electron flow to the Gamma plate
therefore causing triode action.

A word of caution! Since one has a forward biased diode across the power
supply with only the cathode temperature limiting the electron flow, one
must protect the power supply from the possibility of excessive current.
Initially, I used a #47 lamp in series with the anode and the power supply.
I got tired of replacing the lamps when I was experimenting with various
Gamma currents or electron space charge buildup and resorted to a voltage
divider setup allowing 75 volts at 15 ma. from a 180 volt supply. The design
wattage of the voltage dropping resistor was selected so it could safely
dissipate the entire 180 volts in conditions when the Gammatron currents
became excessive either due to too high of a heater voltage or electron
space charge buildup.

I suggest that you visit http://www.tubecollectors.org/ for information
regarding the tube collector. I just noticed that the editor has not listed
the February, 2006 on the website yet. However, all previous issues are
currently listed. Information on the most recent issue containing my article
should be appearing in the next couple days.

Have fun experimenting ---- That is what ham radio is all about.

Bob, K2GLO     

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Jim Candela
Sent: Friday, February 17, 2006 4:09 AM
To: Discussion of AM Radio
Subject: RE: [AMRadio] Re: AM Transmitter Advice??


John,

    Check this out:

http://uv201.com/Tube_Pages/heintz-kaufman.htm


Jim
WD5JKO

--- John Coleman ARS WA5BXO <wa5bxo2005 at pctechref.com>
wrote:

> OK BOB!
> 	You got my attention. Explain more.  I hope I'm not
> a sucker
> here.  I have seen and extremely low mu amplifier
> circuit (common
> cathode) made by reverse biasing the plate of a
> triode and forward
> biasing the grid where output is taken from the grid
> and input is on the
> plate.  So I know that weird stuff does exist.
> 
> John, WA5BXO
>  
> 
> -----Original Message-----
> From: amradio-bounces at mailman.qth.net
> [mailto:amradio-bounces at mailman.qth.net] On Behalf
> Of Bob Deuel
> Sent: Thursday, February 16, 2006 6:05 PM
> To: 'Discussion of AM Radio'
> Subject: [AMRadio] Re: AM Transmitter Advice??
> 
> Hello Larry and all:
> 
> Larry's tongue in cheek comment employing 866's as a
> linear amplifier
> tube
> prompted me to contribute the following: Certain
> full-wave rectifiers
> can be
> configured to amplify or oscillate. I have built
> audio, Hartley and
> Simpson
> oscillators using only 6AX5GT's full-wave rectifiers
> as the sole active
> device. These were displayed at 2004 Mid-Atlantic
> Antique Radio Club
> Meet
> and actually won a Blue Ribbon.
> Late last year I built an AM transmitter consisting
> of a Hartley
> oscillator
> modulated by an AM modulator using only 6AX5GT
> full-wave rectifier tubes
> as
> the active devices. No solid-state magic, just
> simple full-wave
> rectifiers.
> The basic concept is that of the Heintz and Kaufman
> gridless Gammatron
> circuits. The transmitter was set up for the
> broadcast band and works
> fine.
> It has been publicly demonstrated a couple times now
> and a write up
> including the circuit was published in the February,
> 2006 issue of the
> "Tube
> Collector" magazine which is the bi-monthly magazine
> published by the
> Tube
> Collectors Association, Inc. It is fun to make
> full-wave rectifiers do
> more
> than just rectify.
> 
> Bob, K2GLO   
> 
> -----Original Message-----
> From: amradio-bounces at mailman.qth.net
> [mailto:amradio-bounces at mailman.qth.net] On Behalf
> Of ne1s
> Sent: Thursday, February 16, 2006 10:36 AM
> To: Discussion of AM Radio
> Subject: [AMRadio] Re: AM Transmitter Advice??
> 
> Donald Chester writes: 
> 
> > 
> >> Assuming one is going to build a linear, and so
> putting aside other 
> >> issues
> >> such as linear vs plate modulation, why do you
> think it makes a 
> >> difference
> >> what tube is used? Are you referring to running a
> linear at greater
> than
> >> legal limit?.
> > 
> > Well, go ahead and try building a legal limit
> linear that runs a pair
> of 
> > 807's in the final. 
> > 
> 
> Yeah, or a pair of 866As.... 
> 
> Sorry (the devil made me do it). 
> 
> 73,
>  -Larry/NE1S
>
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