[Patrick Turner]

Bret Ludwig wrote:

Using one choke as a first element is almost unheard of. Usually you
have two chokes, a "swinging" and a "smoothing" choke. These are two
different parts. Their combined weight and cost is usually more than
the power transformer.

The swinging choke and smoothing choke indeed make a nice PS usually
for clean supply to HV gear, such as a transmitter or class AB modulator
using tubes like the
813, 211, 845, 1606 etc.

The caps don't need to be huge C value, and can be sealed 20uF paper in
oil rated for
1,000V or more. The LCLC arrangement is then essential for a smoothed
supply
where we are using 866 rectifiers and low value C.

Such gear has never ever been bought by home users of hi-fi gear.
Many radio amateurs would be familiar with such choke input techniques.


Best source of information for small apps (under 1 kW) is the ARRL
Radio Amateur's Handbook from the AM ham era. Overseas resources like
RSGB, often superior to ARRL or W6SAI on some subjects, do not cover
this too well because high power AM was mostly exclusive to wealthy
hams who bought factory rigs outside the US.

A friend of mine here bought an 800W capable AM transmitter as ex-army
surplus gear
in about 1962, and he still has it. It has 813 PP output, and lots of
807s within, plus
LCLC type PSU.

As a thouroughly illegal ham using this he found he could reach around
the world
using his shed roof as the antenna. He posed as VK211, which was the
callsign of a guy who'd died
just before be began his pirating which went on for years without anyone
detecting anything,
although the PMG did get supsicious.
The PMG ( commumications authority ) once went searching for the origin
of the this high
power signal but he watched with amusement as the direction finding van
drove right past his house,
unable to indicate direction, because the signal totally overloaded the
gear they had.
He worked for the PMG, and knew what their capabilities were....


All AM ham transmitters over a few watts, or almost all, used high
level plate modulation. An audio amplifier, standard in all respects
but one, of approximately half the key-down CW power of the
transmitter was used. The change was the output transformer which was
an air gapped unit like a SE unit because the plate current of the
transmitter flowed through its primary.

And maybe saturable reacatnces were used... all rather quaint....

Patrick Turner.