On Apr 24, 7:35*pm, Bill M wrote:
David wrote:
On Apr 20, 1:34 pm, David wrote:
Looking for Crystal Radio Receiver Circuits, that have a voltage
quadrupler to increase headphone volume without batteries or AC power.

On my original post i was, and still looking for a quadrupler circuit,
not information on why it does not work.

Sorry. *Frankly I've never seen one but I guess you could lash something
together easy enough. *May try asking over at the Rap-n-Tap forum. *If
anybody knows of one that group would surely know.

Rgds,
Bill


Greetings; I just happened upon this discussion while searching for
more crystal set information. I've tinkered with "free power" sets
back in the seventies, and am currently an experimenter/collector with/
of vintage radio. It is possible to build voltage triplers and
quadruplers for crystal radio, but it isn't practical. No one does it
since it doesn't work very well. Pretty crappy.too much loss in
diodes Waste of time. BUT, certain full wave set-ups DO work and
work quite well. There has been much engineering and engineer-speak
concerning crystal radio. Much SPICE work, much analysis's, many
mathematical equations. But there appears to be a paradigm going on
that makes it verboten to consider the lost cycle. Standard crystal
sets (and those that use several detector diodes in parallel like the
schottky 2380) are half wave rectifiers. What about the other half of
the Electromagnetic wave? Half the potential power of the radio wave
is gone, wasted. It can be recovered and utilized. But it must be
done correctly. At any given cycle the current must flow through one
diode, and only one (I'm considering multiple diodes in parallel as
one here). So bridge rectifiers are out. Triplers and quads are
out. You can use a coil with a center tap, essentially two half-wave
rectifiers, each one detecting half the signal. Another way that
works is making a half-wave voltage doubler. Imagine a standard
crystal diode set-up; tank coil on the left, diode at the top with
cathode line to the right facing the 'phones, and the anode end facing
left towards the coil. Now add a fairly large capacitor, mica or low-
loss metal film or poly inserted between the diode's anode and the
coil. The system still works as a standard crystal set; except for a
little capacitive reactance, the signal passes along as usual. Now
picture a second diode with it's cathode end connected to the
connection between the capacitor and the first diodes anode. Again,
this setup works like a standard crystal radio, when the cycle is
positive. But now, when the cycle turns negative, instead of the
negative cycle being blocked by the first diode and being wasted, the
negative cycle is "shorted" out by the second diode, and goes to
ground. Shunted to ground, but not wasted. The capacitor now has a
charge on it equal to the RMS value of the wave times the square root
of 2, or 1.414. It's been charged. Electrons are piled up on the
right hand side of the capacitor, towards the anode end of the first
diode. Now when the signal swings positive again, the electrons of
the signal pass around through the negative/ground side, through the
'phones, through the cathode end of the first diode, and out the anode
of the first diode, where they encounter the capacitor. It doesn't
exactly work like this, but this is a good way to get the picture.
Anyway, the electrons going out the anode end encounter the capacitor
where electrons are piled up/stored on the capacitor's plate facing
the anode end of the diode. The two charges combine, nearly doubling
the power.
Try at least a 1000 (.001 uf) picofarad capacitor. Some folk use 5000
or a .01uf. You should still use a filter cap across the 'phones,
like about 500p.
I've seen where people have built such a circuit, and claim it's no
good. One such circuit only had a 30p capacitor. Of course it didn't
work! There's nothing new about this type of voltage doubler that
makes use of the other half of the wave. There's nothing new about a
full-wave rectifier using two diodes (one for each wave cycle) and a
center-tapped coil. it's been published back in the early 20th
century. With a good antenna you can drive a high-impedance speaker!

wrote:

What about the other half of
the Electromagnetic wave? Half the potential power of the radio wave
is gone, wasted. It can be recovered and utilized. But it must be
done correctly.


Hi tack. I've seen you on some of the other forums.


No disagreement in that you can recover the other half and add things
together. I offered the full-wave centre-tapped coil as an example.

But that only works for humble 'local station' circuitry.

How can we do the same thing for low-level/high selectivity circuits? I
dunno. The predominant thinking is that you get the voltage 'gain' by
going to the moon with hi-q rf circuitry which is at odds with a bunch
of diodes configured as a multiplier because of the loading factor. Or
having some other mass of wire on the same coil form. Kills the Q and
consequently kills off the voltage gain.

Now if a guy has enough room...I'm only being partly facetious...to have
tuned circuit A separated far enough away from tuned circuit B (or C or
D) he could probably find a way to combine them. A good hi-q circuit
might require 12 inches plus of physical isolation. I've not seen
anybody approach it that way . Probably because the expense and effort
of multiple tanks is mitigated by less effort on a good single tank.


Crystal sets remain to be a fascinating 'open book' for experimentation.

-Bill