The best AM receiver

Answering the question of "What's the best AM receiver/tuner I can
get" is contingent on your definition as to what "best" means. If you
want the best quality audio from local stations with a good antenna
and ground, the old crystal radio is still the best.

For the uninitiated, a "crystal radio" has nothing to do with a
crystal in the modern sense, the resonant piece of quartz used to
define frequency in RF circuits including most every computer in
existence. Crystal tuning for receivers and transmitters goes back to
the twenties or thirties, but in this context we mean a crystal
detector,i.e., a semiconductor diode, called a "crystal" because in
the old days it consisted of a fine wire poked onto a chunk of lead
pyrite or some other rock so that the wire or needle and rock formed a
semiconducting PN junction. The actual tuning is done with LC
circuits, traditionally made from a coil wound on a Quaker Oats
container or similar. With a good antenna and ground, you could pick
up enough RF so when the modulated signal was detected it would
directly drive a pair of the old high impedance watchcase headphones.
No battery was needed: it worked for free. All the energy used to
drive the diaphragms of the headset came from the transmitter, tens,
hundreds, perhaps under ideal conditions thousands of miles away.

A surprising amount of energy can be had this way. Within a few miles
of a 50 kW daytimer or clear channel station, enough actual power can
be developed-with the right RF and output matching- to light a
flashlight bulb and certainly a LED. In fact, Klipsch used to have a
demonstrator radio that would drive the midrange horn of a Klipschhorn
or similar and provide a surprisingly loud signal in the room. At
night one could listen to several stations in most cities almost as
loudly as a nine-volt-powered transistor portable could play, and with
better fidelity.

Of course, with enough power, an inadvertent crystal set can be
accidentally assembled with humorous consequences-such as the elderly
couple who complained that when Howard Stern was on the local station,
sounds surprisingly resembling penis, vagina, and Baba Booey would
emanate from the tub of their washing machine-or tragic ones such as
the occasional premature dynamite explosion on a road project when
some trucker with a 'foot warmer' keys his trusty CB rig.

A crystal radio, then is a passive, tuned-radio-frequency RF tuner. If
the output were plugged into a good high impedance amplifier, the
result is audio amplified as loud as we want it, just like any other
line level audio source. In the beginning days of high fidelity, the
RF coil houses like Miller introduced passive AM tuners that were
nothing more than the old crystal radio. Because of the gain in a good
preamp and power amplifier, you got good results in many cases with
only a small antenna. Sensitivity and selectivity were not of the
highest order, but with a good local station without much
interference, the fidelity was superb. And, it still is. These passive
AM tuners can still be found fairly cheaply or you can build one
yourself, like generations of boys did in the past.

If on the other hand, you want broadcast band overall DX capability,
you can either buy a serious communications receiver, or the next best
thing-an old car AM radio converted to work at home. By the end of
WWII, car radios were generally better radios than their domestic
counterparts. They had to be, because of the environment they worked
in. This was true until AM functionality came to be regarded as just a
legacy as compared to FM performance around the early 1980s, at which
time they cheapened the AM sections of the radios.

You want an AM only set for best Am performance. Either tube or solid
state sets will work fine, but avoid like monkey plague the GM hybrid
radios with 12 volt plate supply tubes and transistor output. Avoid
Wonderbar or other auto tune radios: in fact a non-push-button set is
best if you can find one made by Delco, Philco Ford or other Big 3
supplier. Avoid most aftermarket or foreign radios: the only ones any
good are Blaupunkts or Beckers worth a lot to VW or Mercedes buffs.
Overall, I think Delcos are the best. YMMV.

Needless to say, avoid ones with tape players, CB radios or the like.
The cheapening started before digital came out, so avoid digital units
entirely. You want either a 1947-1955 tube set or a 1964-1975 or so
solid state one.

In the case of the solid state set you just need a 12.6 volt DC
supply. These can be bought or built. It does not need to be regulated
but it should be pretty quiet.

Tube sets can be run the same way, but it's inefficient. Instead,
remove or disconnect the stock vibrator, power transformer and
rectifier and provide a B+ supply with a conventional HV transformer,
diodes and filter caps. You will also need a 6.3 or 12.6 volt heater
supply of course. Generally, the limiting sonic factor is the stock
output transformer, which you will want to replace with a larger and
heavier one for a single ended amp using whatever tube is in there,
usually a 6V6.

Most of the pure tube sets are for 6 volt supply, meaning they'll have
6 volt heater tubes, but some were 12 volt for the few cars and trucks
that were 12 volt before the hybrid and full transistor sets came in.
Usually those just have a different power transformer and use 12
versus 6 volt heater tubes. In some cases they seriesed the heaters on
the small signal tubes and just used a 12V6, or used other odd
arrangements. Almost always the filaments were run directly off the DC
supply though.

Johnson VIKING VALIENT

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