[Heathkit] Heath Warrior as an AM amplifier

[Carl]

----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: <heathkit at mailman.qth.net>
Sent: Tuesday, January 17, 2012 11:52 AM
Subject: Re: [Heathkit] Heath Warrior as an AM amplifier


>
> ----- Original Message ----- 
> From: "James M. Walker" <chejmw at buffalo.edu>
> To: <heathkit at mailman.qth.net>
> Sent: Tuesday, January 17, 2012 7:11 AM
> Subject: Re: [Heathkit] Heath Warrior as an AM amplifier
>
>
>> Or a classic case of "YOU CAN'T GET THERE FROM HERE" !
>> Strange!
>> Jim
>> WB2FCN
>
>    Linear amplfiers were used for many years by broadcast
> stations. One characteristic of these transmitters is low
> plate efficiency. A Class-B linear will have, in principle,
> no plate current in its quiescent state, i.e. no signal, and
> about 66% with maximum signal. When used for AM the carrier
> is there all the time and is well below the maximum output
> of the amplifier so its efficiency for the carrier is quite
> low. Since even processed speech and music has a high ratio
> of peak to average level the average or "all day" efficiency
> of AM linear amplfiers was not much better than the
> efficiency for the carrier only. While these transmitters
> had good signal quality the low efficiency made them
> expensive to operate especially since most high power
> transmitters required lower level linear amplifiers as
> drivers. There began to be a demand for something better.
> One answer was the Dougherty circuit of Western Electric,
> which had something like 65% all-day efficiency but was hard
> to keep tuned up and had rather high distortion. Other
> manufacturers began to offer plate modulated transmitters.
> These had fairly high efficiency but required expensive
> modulation transformers. There were modifications of the
> original Dougherty circuit that substantially improved its
> performance, particularly the ones patented by James O.
> Weldon, of Contenental Electronics. Transmitters of this
> type are currently made. Another approach was the pulse
> modulated transmitter (forgotten the inventor), capable of
> very high efficiency, this is the basis of the transmitters
> made by Harris, and I think now by others. There were some
> other approaches but amateurs has switched to SSB before
> these became available. The high efficiency linears have no
> advantage for carrier suppressed signals so are not found in
> ham gear.
>     Using a linear amp for AM is a throwback to the 1930s.
> A good deal of technical literature of the time covers
> broadcast transmitters using them and may be of interest.
>
>
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com
>


Many SWBC stations use AM linears today at the 100KW and up level.

The old 500KW WLW flamethrower of the 30's was a linear final but they had 
their own cooling pond outside the building for thos water cooled finals.

Today a linear makes very good sense considering the cost of owing and 
electricity of a complete modulator deck and low level stages (Plus mods to 
convert a linear to Class C) unless you can score a surplused AMBCB TX and 
convert to a few ham bands.

A BC-610 with the mod preamp/driver is another consideration. There is also 
the T-368 which was the next generation. Both are widely used today on ham 
bands.

Carl
KM1H






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