On Apr 20, 7:40*pm, Paul Keinanen wrote:
On Mon, 20 Apr 2009 11:34:49 -0700 (PDT), David
wrote:

Looking for Crystal Radio Receiver Circuits, that have a voltage
quadrupler to increase headphone volume without batteries or AC power.

I assume you are talking about a broadcast receiver for frequencies
below 1600 kHz. At such frequencies and with a typical 500 pF variable
capacitor, the impedance levels for an LC resonant circuit is quite
high.

Loading it with a crystal detector and some low impedance (30 or less)
headphone will load the resonant circuit quite heavily, reducing the
output quite heavily.

In the old days, the typical impedance of a headphone might have been
about 2000 ohms, loading the resonant circuit much less. In order to
cause a similar loading to the resonant circuit using current
headphones, you need an audio transformer with 2000:30 impedance ratio
or 8:1 turns ratio.

Paul OH3LWR

Hey OM

I know they still make 2000 ohm headphones, Philmore still makes them,
then there is a crystal headphone.
A crystal headphone you can make yourself. It''s just a crystal
microphone in reverse. I seen the QST article on how to make a crystal
microphone.

But the best bar none, is a balanced armature headphones, those things
are self powered, or so they say. And balanced armature headphones
cost an arm and a leg too.

73 OM

de n8zu

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.

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

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

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

Hi David - I think this idea will not work well for the reasons others
have already given - (a) the forward voltage drop of the diodes (2
instead of 1) which means that you must have an rf signal of around
1.2v instead of just 0.6v before you hear anything at all, and (b) the
question of the availability of power. A quadrupler will not increase
the very small amount of power picked up by the aerial.

However, all is not lost. Other enthusiasts have been at work with a
crystal set which uses a 'zero gate-threshold' FET as a form of
passive synchrodyne detector. The incoming signal opens and closes
the conducting channel of the fet at the same frequency as the signal
applied to the earphones through the channel (they are both the same
signal). This give synchronous mixing and hence detection of the rf
envelope. The advantage is that the fet has low and high impedances
in the right places (low channel impedance, high gate impedance) and
so is highly efficient.

Forgive the long posting, but here is something copied from the GQRP
Yahoo group, with references. Andy G4OEP

Hi to everyone on the list,

For those who have been following the "High sensitivity Crystal Set"
and "More ham xtal set DX heard tonight on 80m" threads on this list I
should like to share my recent experiences/observations using the
ALD110900A device as a synchronous detector/crystal receiver.

The high sensitivity crystal set was featured again in the current
Rad-Com (June 2007 edition, page 60) and the RSGB have made available
a limited number of the ALD110900A devices on a
first-come-first-served basis via RSGB sales. I obtained a small
number of the ALD110900A devices so I could compare the performance to
the 2N3819 jfet which I had been using in my version of the receiver
based on the design by David Cripe (NE4AM) in his article "Nostagia
For The Future" (Amateur Radio Today, Dec. 1995 pages 14-16) a copy of
which can be found on this web page...

http://members.wideband.net.au/gzimm...tors/FET1.html

The article referenced above was the inspiration for the more recent
article in the January edition of QST, a copy of the QST article
appears here...

www.arrl.org/qst/2007/01/culter.pdf

Observations/Comments:
I found the best results are obtained using the design described by
David Cripes (NE4AM) in his 1995 article. His use of two tapped tuned
circuits (band pass filter arangement) permits precise matching of
both the antenna and the load, both of which are vital for best
crystal set performance. In operation I found the receiver to perform
very well with resuls comparable to a BC receiver, seperation of
stations was readily achieved with good volume and loud enough for
this "deaf old coot" to be able to listen to news broadcasts etc and
understand what was being said. The antenna used is about 60 feet of
wire and a central heating system counterpoise. My receiver shares the
two 4 inch diameter coils used in the NE4AM design, it also shares the
jfet (2N3819) with gate bias as described by David in his article.

The June Rad-Com article does not seem to place enough emphasis on the
importance of matching the ALD110900A sorce/drain impedance and load
(headphones) to the tuned circuit. My opinion is that best results are
obtained with a good selection of tappings on the coil as described by
NE4AM. The ALD110900A (or jfet plus negative gate bias supply)
circuit demonstrates its superior performance over the OA81, OA91 etc
style detector circuits when detecting weaker signals. Signals which
are simply inaudible to the OAxx style detectors are rendered audible
by the ALD or jfet synchronous detector design. The ALD or jfet design
definately offer better performane for "crystal set DX for 80 Mtrs" or
other similar applications.

I note that in both the January QST and June Rad-Com articles they
used a low impedance telephone earpiece via an autotransformer for
matching. In the Rad-Com article they said that "an old pair of Hi-Z
headphones" was substituted for the low-Z earphone/autotransformer
with no noticable improvement. I can only conclude that the "old pair
of Hi-Z headphones" must have been very poor quality or had weak
magnets, in my tests substituting my pair of "old Hi-Z headphones"
into the circuit made a very significant difference. I tested several
low-Z telephone earpieces (all worked) but the Hi-Z phones (4000 Ohms)
consistently outperformed the low-Z units. Its also worth pointing out
that the difference was most notable on weaker signals. On strong
(local) signals the difference was much less obvious. I currently do
not have a crystal earphone to test with but I suspect a crystal
earphone would also outperform most low-Z earphones/matching
transformer configurations.

And finally:
I would strongly advse anyone who is thinking about experimenting with
this form of synchronous detector to first read David Cripes (NE4AM)
article as a starting point and also give serious consideration to
using a 2N3819 jfet plus adjustable negative gate bias supply in
preference to the ALD110900A device. The only significant advantage I
can see with the ALD device is that its zero Volts gate threshold
avoids the requirement for the seperate negative gate bias supply
required by the jfet arangement and thus saves a few components.

The RSGB are currently offering the ALD110900A devices for 4 UK pounds
each (including UK postage) but if you already have a 2N3819 (or
similar N-ch' jfet) in the junk box then try that first with an
adjustable negative gate supply and evaluate the circuit for yourself
before spending your 4 pounds. One additional advantage of the jfet
plus negative gate bias approach I have found is that by making the
bias adjustable (front panel control) you can improve
performance/sound quality on strong signals. The bias point for best
sensitivity and lowest distortion (on stronger signals) are not the
same so the ability to make bias adjustments "on-the-fly" is an
advantage.

Conclusion:
If you are building a crystal set for the "local" station(s) then I
see no real advantage in bothering with the syncronous detector
approach but if you want a crystal set with highest possible
performance then the syncronous detector plus tapped coils (for
matching) gives outstanding performance.

I wonder, has anyone else on this list experimented with the ALD
devices and if so what are your experiences?

73,s to all on the list.

Des (M0AYF G-QRP 9788)