Hooking up Output Transformer Crystal Radio Plans Help!! Help!!!

[Capoot]

You will probably be disappointed in your crystal radio's ability to drive a
speaker even with an optimal transformer. The transformer will allow you to
use commonly available 32 ohm stereo phones. Hook up the phone jack so that
the phones are in series. While your ohmmeter will not measure impedance,
it will give you an indication of which windings are high and low. Use the
highest resistance pair for the input and the lowest for the speaker or
phone. Power transformers are optimized for 60 cycles but will operate at
audio frequencies. Use the lower resistance filament winding for the phone.
Crystal earbuds were by far the best transducers that I ever used on my
sets. No transformer needed and plenty of volume even with minimal or no
antenna. Hook up two in parallel. Mouser has them (25CR025, 25CR035,
25CR060) for $2.03 each.
http://www.mouser.com/catalog/616/948.pdf
I had a lot of fun playing with crystal set circuits in my youth. A great
introduction to radio/electronics.
Ray

 

[John Woodgate]

I read in sci.electronics.design that Spehro Pefhany <speffSNIP@interlog
DOTyou.knowwhat> wrote (in <[email protected]>)
about 'Hooking up Output Transformer Crystal Radio Plans Help!!
Help!!!', on Wed, 31 Dec 2003:

Ignoring the impedance matching issue, would they be as efficient as a
modern rare-earth magnet "Wallkman" type earbud?

I've never had occasion to compare them, but I could if I get a round
tuit. My impression is that the high-impedance phones are a lot more
sensitive.

 

[Jeff Goldsmith]

It's possible to drive a speaker if you live in the strong local
field of a trasmitter. I used a double-tuned antique loose coupler and
detector with my 80 meter dipole as the antenna and had two volts DC of
detected carrier. Capacitor coupled to a twenties vintage horn speaker
and my local 1000 watt station on 1030 made a decent amount of sound.

Just the one nearby (4 miles away) station had enough level to hear
out of a speaker.

With just the loopsticks or a typical strung-out antenna, no. With a
large antenna and good tuned circuits and detector, yes, but a nearby
local station only.

Jeff Goldsmith

 

[N. Thornton]

It's possible to drive a speaker if you live in the strong local
field of a trasmitter. I used a double-tuned antique loose coupler and
detector with my 80 meter dipole as the antenna and had two volts DC of
detected carrier. Capacitor coupled to a twenties vintage horn speaker
and my local 1000 watt station on 1030 made a decent amount of sound.

A 1920s horn speaker will almost certainly be moving iron rather than
moving coil, and these are very much more efficient. Mine makes a
racket on less than 0.1 watt.

If the OP is determined to drive a speaker I would suggest:
1. using a much larger speaker, as 2.5"ers are usually low efficiency
2. making a horn speaker using a moving iron earpiece from an old dial
phone

But realistically, I think a crystal set driving a speaker is most
optimistic. It might have been done once, but in most cases youre
lucky just to get very quiet earpiece reception. A lot of crystal sets
never receive anything.

Your set will have no noticeable selectivity, you will simply hear
whichever station is strongest. Crystal sets are unselective at best:
your voltage doubler and transformer arrangement will kill what little
selectivity there was.

The fussing over using an airspaced tuning cap is pointless, modern
plastic sheet ones are fine. A lot of crystal sets work with no tuning
cap at all, since theyre barely tunable anyway.

The thing about air spaced caps dates back to the 20s when some sheet
dielectric variables had Qs as low as 1, and thus got a very bad name.
This problem disappeared a very long time ago.

You can also make your own tuning cap using foil and oiled paper, with
a thumb screw controlling the compression. Variometers are probably
easier though.


Rare earth magnets in earpieces may help some with efficiency, but
moving coil is still an inefficient technology. Moving iron is better
in this respect, and crystal better still. We use moving coil for its
superior sound quality, the price is low efficiency.


BTW, I'm wondering whether a battery L Cs and neon could be used to
amplify things a bit, does the neon have a neg R range at af, or is it
flip flop only? Anyone know? I dont have the relevant graph.

For the OP, once youve got audio I'd suggest considering a carbon
amplifier. They give excellant amplification, at least excellant in
quantity terms.


Regards, NT

 

[Jeff Goldsmith]

Your set will have no noticeable selectivity, you will simply hear
whichever station is strongest. Crystal sets are unselective at best:
your voltage doubler and transformer arrangement will kill what little
selectivity there was.

I don't think the doubler is needed because there is only so much
energy from the signal. The doubler changes the optimum impedance but
not the amount of energy available.

The fussing over using an airspaced tuning cap is pointless, modern
plastic sheet ones are fine. A lot of crystal sets work with no tuning
cap at all, since theyre barely tunable anyway.

A double tuned loose coupler gives a decent amount of selectivity. I
would certainly not characterize it as barely tunable. This could be
true of simpler crystal receivers with only one tuned circuit.
With a large, old loose coupler and two 43-plate variable condensers
(primary in series, secondary in parallel) my 1000 watt local station on
1030 was not stopping me from listening to 850 KOA Denver and 820 WBAP
Dallas (whichever was stronger) with an audio amplifier. I would say
the selectivity was such that you would hear the strongest station of
five or six channels while tuned to 830KC.


Jeff Goldsmith

 

[Robert Baer]

A 1920s horn speaker will almost certainly be moving iron rather than
moving coil, and these are very much more efficient. Mine makes a
racket on less than 0.1 watt.

If the OP is determined to drive a speaker I would suggest:
1. using a much larger speaker, as 2.5"ers are usually low efficiency
2. making a horn speaker using a moving iron earpiece from an old dial
phone

But realistically, I think a crystal set driving a speaker is most
optimistic. It might have been done once, but in most cases youre
lucky just to get very quiet earpiece reception. A lot of crystal sets
never receive anything.

Your set will have no noticeable selectivity, you will simply hear
whichever station is strongest. Crystal sets are unselective at best:
your voltage doubler and transformer arrangement will kill what little
selectivity there was.

The fussing over using an airspaced tuning cap is pointless, modern
plastic sheet ones are fine. A lot of crystal sets work with no tuning
cap at all, since theyre barely tunable anyway.

The thing about air spaced caps dates back to the 20s when some sheet
dielectric variables had Qs as low as 1, and thus got a very bad name.
This problem disappeared a very long time ago.

You can also make your own tuning cap using foil and oiled paper, with
a thumb screw controlling the compression. Variometers are probably
easier though.

Rare earth magnets in earpieces may help some with efficiency, but
moving coil is still an inefficient technology. Moving iron is better
in this respect, and crystal better still. We use moving coil for its
superior sound quality, the price is low efficiency.

BTW, I'm wondering whether a battery L Cs and neon could be used to
amplify things a bit, does the neon have a neg R range at af, or is it
flip flop only? Anyone know? I dont have the relevant graph.

For the OP, once youve got audio I'd suggest considering a carbon
amplifier. They give excellant amplification, at least excellant in
quantity terms.

Regards, NT

A neon bulb can be biased in the negative resistance region and become
rather sensitive to radiation (RF, light, ionizing particles), and as
such can be used as an amplifier (similar to one of the uses of Esaki
diodes AKS tunel diodes).

 

[Robert Baer]

A 1920s horn speaker will almost certainly be moving iron rather than
moving coil, and these are very much more efficient. Mine makes a
racket on less than 0.1 watt.

If the OP is determined to drive a speaker I would suggest:
1. using a much larger speaker, as 2.5"ers are usually low efficiency
2. making a horn speaker using a moving iron earpiece from an old dial
phone

But realistically, I think a crystal set driving a speaker is most
optimistic. It might have been done once, but in most cases youre
lucky just to get very quiet earpiece reception. A lot of crystal sets
never receive anything.

Your set will have no noticeable selectivity, you will simply hear
whichever station is strongest. Crystal sets are unselective at best:
your voltage doubler and transformer arrangement will kill what little
selectivity there was.

The fussing over using an airspaced tuning cap is pointless, modern
plastic sheet ones are fine. A lot of crystal sets work with no tuning
cap at all, since theyre barely tunable anyway.

The thing about air spaced caps dates back to the 20s when some sheet
dielectric variables had Qs as low as 1, and thus got a very bad name.
This problem disappeared a very long time ago.

You can also make your own tuning cap using foil and oiled paper, with
a thumb screw controlling the compression. Variometers are probably
easier though.

Rare earth magnets in earpieces may help some with efficiency, but
moving coil is still an inefficient technology. Moving iron is better
in this respect, and crystal better still. We use moving coil for its
superior sound quality, the price is low efficiency.

BTW, I'm wondering whether a battery L Cs and neon could be used to
amplify things a bit, does the neon have a neg R range at af, or is it
flip flop only? Anyone know? I dont have the relevant graph.

For the OP, once youve got audio I'd suggest considering a carbon
amplifier. They give excellant amplification, at least excellant in
quantity terms.

Regards, NT

*** To the OP:
That transformer is not really what is called for, but it is useable;
the Xformer should be 20K input Z.
Been too long to remember how it goes; use the highest resistance tap
for input.
One must load one winding in its rated impedance, then measure the
others at 1KHz.
If you have a lot of fine wire, it could be done, but i do not have
any equations for audio transformers, only line power transformers.
An audio tranformer uses a different "steel" core, and the laminations
are thinner and sometimes are of varying thicknesses, to handle the wide
frequency range involved.
If one could get rather thin laminations from a power transformer (say
one rated for 400Hz or higher), then wind as if one was going to use it
for (say) 50Hz, the result would not be too bad, especially for a
"home-brew" job.
How the primaries and secondaries are placed, along with using "pi" VS
"linear back and forth" etc will also affect the overall frequency
response, leakage inductance and inter-winding capacitance.
Refer to the RCA Radiotron Designer's Handbook for details.
"W" does, in fact, mean "watts"; what you have is a 70.7V line
transformer for public address systems,and is not really for this
application.

 

[John Woodgate]

I read in sci.electronics.design that N. Thornton <[email protected]>
wrote (in <[email protected]>) about
'Hooking up Output Transformer Crystal Radio Plans Help!! Help!!!', on
Thu, 1 Jan 2004:

For the OP, once youve got audio I'd suggest considering a carbon
amplifier. They give excellant amplification, at least excellant in
quantity terms.

You'd have to explain what you mean by 'carbon amplifier'. It's not one
that has been severely overheated. Do you have a source of carbon
microphones? The old telephones are extinct in UK unless you rob a
museum.

 

[James Meyer]

With a large, old loose coupler and two 43-plate variable condensers
(primary in series, secondary in parallel) my 1000 watt local station on
1030 was not stopping me from listening to 850 KOA Denver and 820 WBAP
Dallas (whichever was stronger) with an audio amplifier. I would say
the selectivity was such that you would hear the strongest station of
five or six channels while tuned to 830KC.


Jeff Goldsmith

Back in the late 50's I was listening to Radio Moscow's english language
shortwave broadcasts with a crystal set connected to a three transistor audio
amplifier. I was in central North Carolina at the time.

I was impressed, to say the least. Then I found out that Russia was
probably using the total output of their national electrical grid to power their
transmitters. Still, it's probably a record DX reception.

Jim

 

[James Meyer]

A neon bulb can be biased in the negative resistance region and become
rather sensitive to radiation (RF, light, ionizing particles), and as
such can be used as an amplifier (similar to one of the uses of Esaki
diodes AKS tunel diodes).

A "Radio News" magazine article published in the 40's detailed many
different crystal detectors. One was a carborundum crystal. Some experimenters
related their experiences with them and noted that they performed quite a bit
better with a battery, probably around 3 volts, in series with the crystal.
There was speculation at the time that there was actual amplification of the RF
signal going on as well as rectification.

Jim

 

[James Meyer]

I read in sci.electronics.design that N. Thornton <[email protected]>
wrote (in <[email protected]>) about
'Hooking up Output Transformer Crystal Radio Plans Help!! Help!!!', on
Thu, 1 Jan 2004:


You'd have to explain what you mean by 'carbon amplifier'. It's not one
that has been severely overheated. Do you have a source of carbon
microphones? The old telephones are extinct in UK unless you rob a
museum.

Two single-edge razor blades mounted in a block of wood with their edges
pointed up and a piece of carbon from the inside of a "lead" pencil laid
perpendicular across the edges, will create a very usable carbon mike. Make
electrical connections to each blade, of course.

Jim

 

[Jeff Goldsmith]

I've used bias with good affect on some detector diodes, and others it
gives no improvement. My connection has been a battery with 2.2 meg
resistors from each terminal connected to the diode for a small forward
current.

Jeff Goldsmith

 

[- - Bill - -]

You'd have to explain what you mean by 'carbon amplifier'. It's not one
that has been severely overheated. Do you have a source of carbon
microphones? The old telephones are extinct in UK unless you rob a
museum.

The old military "sound-powered" headphones seem to be the best
recommendation by the serious xtal radio enthusiasts. Here's some links
for further reading.
http://www.webex.net/~skywaves/SoundPwr/soundpwr.html
http://www.webex.net/~skywaves/xtalset102/headsets.htm

In regard to "selectivity", you can go nuts and make a very selective
xtal set. A friend of mine in suburban LA has logged 20-odd stations
and heard as far away as San Francisco and Utah.
Back to the original question, its difficult to get anything other than
a strong local thats going to drive any sort of speaker without further
amplification.

-BM

 

[Brenda Ann]

Back to the original question, its difficult to get anything other than
a strong local thats going to drive any sort of speaker without further
amplification.

But if you have that strong local, it is quite fun. I accidentally created a
crystal set with a voltage doubler when I was 13. We had a 5000 watt station
about half a mile away, and this thing drove a 6" speaker directly off the
detector quite well. I had to cover the speaker with a blanket, etc. to keep
my dad from yelling at me to turn it off.

While I was working on the new transmitter building for 50,000 watt KKSN AM
in Portland, OR, I wanted to listen to the radio at the worksite... needless
to say, this was very problematic in such a high RF environment.. so I
brought from home an old 12" two-way speaker, a home made loop antenna, and
a 1N4003 diode.. you can guess the rest..

 

[[email protected]]

Lo again,

I am the one who started this thread and first of all, I want to thank
everyone for their replies. Some fantastic info. The whole reason I
wanted to build this set was because I thought it would drive a
speaker with no amplification or power. I had dreams of listening to
Art Bell at night without a set of headphones or a earphone stuck in
my ear. I think I may have put too much faith in the authors dreams.


http://hibp.ecse.rpi.edu/~john/xtal.html

From the authors description I was thinking it was using two seperate
detectors to detect both sides of the AC radio wave and then adding
them togther to get twice the output of a regular crystal set. From
reading some of the replies, I take it that it won't quite work out
that well.

I am still going to build the set. I have a good long wire antenna
and am hoping the circuit will work. I am also going to be getting a
real output transformer like the author specified in the plans in the
next week or so. I have had very good results with single loopstick (
Inductively tuned) sets in the past. Most of the time I don't even use
a variable capacitor to tune my sets, just a 100pf fixed. I am not
sure why I have such good luck with ferrite loopsticks. If you vary
the inductance or the capacitance of the tank circuit it seems like it
should give the same results (right?!). I have been able to get 10+
stations during the day and even more at night with pretty plain jane
designs using just a ferrite loopstick to tune them. The sets I build
with a 365 pf air variable and a tapped air coil don't seem to work
nearly as well. Only problem ferrite loopsticks are tough to find. I
have a few and I just recycle them. Anyone know a source for these
little buggers??! If anyone has a bunch they want to sell, please
email me.

I build plans from books but most of my inspiration comes from these
two web pages.

http://www.thebest.net/wuggy/

http://www.schmarder.com/radios/crystal/index.htm

It is a very fun pastime. I still dont understand much of what I
build but I am trying...Thanks again for everyones help in this
thread.

 

[John Woodgate]

I read in sci.electronics.design that James Meyer <[email protected]>
wrote (in <[email protected]>) about 'Hooking
up Output Transformer Crystal Radio Plans Help!! Help!!!', on Fri, 2 Jan
2004:

Two single-edge razor blades mounted in a block of wood with their edges
pointed up and a piece of carbon from the inside of a "lead" pencil laid
perpendicular across the edges, will create a very usable carbon mike. Make
electrical connections to each blade, of course.

Yes, that's more or less a Hughes microphone. But for a carbon
amplifier, if it's what I think it is, you need a conventional carbon
granule microphone with a diaphragm.

 

[Keith R. Williams]

It's possible to drive a speaker if you live in the strong local
field of a trasmitter. I used a double-tuned antique loose coupler and
detector with my 80 meter dipole as the antenna and had two volts DC of
detected carrier. Capacitor coupled to a twenties vintage horn speaker
and my local 1000 watt station on 1030 made a decent amount of sound.

Just the one nearby (4 miles away) station had enough level to hear
out of a speaker.

With just the loopsticks or a typical strung-out antenna, no. With a
large antenna and good tuned circuits and detector, yes, but a nearby
local station only.

When I was in college the RF prof built a crystal set that drove
a loudspeaker rather well off a long-wire antenna to the next
building over. ;-) Indeed he got enough juice out of the air to
light an LED (more interesting than a crystal or any other diode
they tried) used for the detector and drive the speaker. The
thing was still playing (continuously) in the lab the last time I
was there (over 25 years later).

 

[Jim Meyer]

I read in sci.electronics.design that James Meyer <[email protected]>
wrote (in <[email protected]>) about 'Hooking
up Output Transformer Crystal Radio Plans Help!! Help!!!', on Fri, 2 Jan
2004:


Yes, that's more or less a Hughes microphone. But for a carbon
amplifier, if it's what I think it is, you need a conventional carbon
granule microphone with a diaphragm.

A carbon mike produces more electrical output power than the
acoustical input power. An ordinary non-amplified mike can't. A
carbon amplifier is simply a carbon mike closely coupled to a speaker
or earphone. X miliwatts of electrical power goes into the earphone,
X times the earphone efficency (25%?) of acoustic energy comes out of
the earphone and into the carbon mike, and the mike provides an
electrical output that's many more times the original electrical input
to the earphone.

A diaphram isn't really needed. Simply place the homemade mike
so that it touches the earphone/speaker. It then becomes a contact
mike. Probably even more efficient than passing the acoustic energy
through the air.

Jim

 

[Jim Meyer]

Lo again,

From the authors description I was thinking it was using two seperate
detectors to detect both sides of the AC radio wave and then adding
them togther to get twice the output of a regular crystal set. From
reading some of the replies, I take it that it won't quite work out
that well.

I'm not too sure that a full wave detector won't produce more
power than a half wave detector will.

I'll simulate both in LTSpice to see what happens.

Jim

 

[N. Thornton]

I read in sci.electronics.design that N. Thornton <[email protected]>
wrote (in <[email protected]>) about
'Hooking up Output Transformer Crystal Radio Plans Help!! Help!!!', on
Thu, 1 Jan 2004:

You'd have to explain what you mean by 'carbon amplifier'. It's not one
that has been severely overheated. Do you have a source of carbon
microphones? The old telephones are extinct in UK unless you rob a
museum.

Carbon amps were popular in the 20s, especially with crystal sets. As
a pair this was your working class radio, no valves, so the huge
expense of most radios was not there. A carbon amp is basically a
moving iron earphone mated with a carbon microphone: the thing
amplifies quite heavily, if not too faithfully. You can make one by
gluing a toothpick from a carbon mic diaphragm to moving iron earpiece
diaphragm, both removed from a 70s or ealier dial phone.

It works with no toothpick just putting them face to face, but the
toothpick will up the gain aplenty. 12v is the rated working voltage
for the mics.

Where to get them from? I dont know a supplier, I've just kept my eyes
open for scrap old phones.


Regards, NT