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If you collect or restore old radios, crystal sets, early scientific apparatus, vintage test equipment, military surplus, or other unique old technical items, keep me on your watch list.
This replica of the original double-tuned Heathkit CR-1 crystal radio closely follows the specifications of the authentic radio of the 1950's by the Heath Company: This clone first was thoroughly analyzed, researched, and then masterfully built by radio guru Scott Balderson in his home shop. The Heathkit CR-1 Over a period of about five years (1957 - 1962) Heathkit also sold a crystal radio set kit, the CR-1. This radio, like most, tuned the AM broadcast band from 540 KHz to 1600 KHz (kc in those days). The CR-1 is a simple kit that uses a sealed crystal diode instead of a 'cats- whisker'. Search CR-1 Crystal radio and click the oldheadphones.com site. OK, lets break this one down: I was CONSIDERING putting a jumper between the tank rotor and C-4 cold. This would isolate the det stage. The series tuning/coupling w/rotary switch to gnd seems a bit odd and 'overdone',but may be OK.
Posted by Tim On December 26th, 2010 / 17 Comments
My father built this Heathkit CR-1 Crystal Radio for me for my birthday when I was in the 5th grade, circa 1959. I helped ;0)…..
It was a magical device and it got me seriously interested in radio at an early age. I didn’t even realize that the absence of a battery was itself quite an accomplishment. It worked great – keeping me up all hours of the night trying to discover its range limits. In the process I began to learn about what could be used for an antenna, the differences between 1N34’s and power supply rectifier diodes, and why speaking into the headphones would not produce a transmitted signal into the antenna. That should work, right?
Wrong….(I learned after looking through a Heathkit catalog that that feat would require a radio TRANSMITTER! I would drool over actual transmitters in the catalog that could do this – like the DX-100 which I would eventually own).
Note the markings on the right-hand “DET” dial. That was the Detector tuning capacitor. Those little CD (Civil Defense) markings were the frequencies set aside (640 and 1240 KC) in the AM broadcast band for CONELRAD alert messages. These markings were required on all radio receivers built between 1953 and 1963, including this one. COntrol of ELectromagnetic RADiation. Measures taken by the USG to prevent Soviet bombers from homing in on our AM broadcast transmitters as the Imperial Japanese Navy did during the attack on Pearl Harbor. The transmitting sites would change every several minutes as they broadcast emergency information messages. WGBB on Long Island was such a station. A crystal radio would have been very handy at that point.
My Dad installed a Philmore Aerial Kit with its shiny stranded copper wire along the eaves of our house, using TV twinlead standoff ‘s for end insulators. I think the kit originally had two transparent glass insulators for the antenna ends which we didn’t use for some reason. This kit had the porcelain “post” insulators to hold the lead-in in place and a cool conductive strap with Fahnstock connectors at each end to feed the signal under a closed wooden window. There was also a cool copper strap with its own Fahnstock clip which went around the hot water radiator pipe in my room for a ground.
Uninsulated, shiny, stranded copper wire antennas just work better than antennas made with “regular” wire !
Heathkit CR-1 Crystal Radio N6CC
Fun times – I still have the CR-1 and it still works great although the “chicken head” tuning knobs and headset are not original. I’ve built a lot of crystal radios but this one still works the best; due to careful antenna – diode – headset impedance matching.
The Fox Hole Radio
“If it’s stupid – but works – it isn’t stupid” Murphy’s Laws of Combat
During WWI, WWII and later conflicts, many GI’s built “Fox Hole Radios” to listen to news, music, Tokyo Rose, Axis Sally, Lord Haw Haw and probably Hanoi Hannah too. Although the enemy propaganda was laughable, those stations attracted GI’s with their popular music pumped out by powerful radio transmitters. The BBC, Radio Australia and US Armed Forces Radio Stations would carry news from home, music and the all-important sports scores. These Fox Hole radios did not require batteries – they were powered by the signal from the distant radio station as collected by the receiver antenna. They were built and used during the time spent in the “Wait” part of “Hurry up and Wait”. Often in a fox hole. If you were there, you know.
The radio could be built from basic scrap, with the exception of the earplug or earphones; those could be liberated from that enemy tank or aircraft wreckage. That perforated Messerschmitt or Betty could also be a source for the necessary wire for the antenna tuning coil and antenna. The radios were built by the young GI’s who just knew how to make such things. They were the equivalent of today’s techno-geeks and computer hackers (but not the modern kid who thinks “communications technology” is poking their finger at the screen of a Chinese-made iPhone. I’m not interested in those things, but I digress).
This was early 20th century technology and any self-respecting GI was up on it. The omnipresent Ham Radio operators in the Signal Corps probably helped, applying their skills of the day.
I built the Fox Hole Radio described below after a friend produced a WWII Red Cross package containing razor blades among other common items. These were the “Blue Blade” type that had a blue oxide finish, and that finish, in contact with an ordinary pencil “lead”, made a point-contact rectifier. This served the purpose of the “crystal” and “cats whisker” of early crystal radios; it permitted current coming in from the antenna to flow in only one direction. This served to “build up” the antenna signal to a level that could be heard in the earphones by a process known as “detection”.
An attached coil of enamel-insulated wire wound on a piece of bamboo acted along with the antenna wire capacitance to produce a tuned circuit, tuned approximately to the radio frequency band of interest. Experiment with the circuit – you can “short out” coil turns with the paper clip tuning tap; better yet, you can just connect the tap to the razor blade/earphone circuit instead, a more common configuration. This one is REAL basic – but impedance matching and having a healthy signal are the keys to performance.
All that was then required was a long piece of wire for an antenna (that barbed wire fence with wooden posts or a length of infantry telephone “commo wire” was perfect). Plus a ground connection consisting of a metal tent stake or bayonet stuck into the moist soil.
Field improvised ground connection
Above: A typical improvised “ground” connection. A metal tent stake pounded in the ground, kept moist. Here, grounding a PRC-25 radio set. You get the idea.
A few other bits such as a safety pin, a piece of bamboo, plastic water bottle, glass bottle or toilet paper cardboard tube for the tuning coil form. Then a piece of wood from that ammo crate for a chassis, a few screws, thumbtacks or nails and a paper clip to make a “tuner”. In the presence of a strong signal and/or a good antenna it is hard to make this type of circuit not work! The below photos illustrate the basic idea.
Above: The Fox Hole Radio built with a WWII-era “blued” razor blade and pencil lead for the detector. Note the bamboo coil form and the paper clip attached to a cork used to slide along the coil turns to tune the radio. The orange wire goes to the antenna, the black wire to ground. This is the “Deluxe Model” with spring-clips for the external connections.
Fox Hole Radio spring-loaded pencil lead N6CC
Above: Showing the detail of the safety pin used to hold the pencil lead against the razor blade. The copper wire connects the “lead” to the safety pin and the antenna circuit. This assembly functions as the “Cat’s Whisker” of classical crystal radios. My cat was especially appreciative of this alternate design.
Fox Hole Radio – pencil lead and razor blade connection N6CC
The radio is adjusted for best signal by moving the pencil point to different spots on the razor blade to find the “sweet spot” where rectification takes place. (The signal will sound louder). Then adjust the paper clip tuner along the coil turns (put on as many turns as you can – 100 +) to tune and optimize the signal you want to hear. It’s a bit trial-and-error to produce a good signal and it depends a lot upon the height and length of your antenna, the quality of your ground connection, the frequency and local strength of your target station. Or by just getting lucky. (“Chance favors only the prepared mind” – L. Pasteur)
You can also tune the radio by changing the inductance of the coil – make its inductance bigger for lower frequencies by inserting an iron bolt into the bamboo coil form. Or make it tune higher frequencies by reducing the coil inductance by inserting a piece of brass – that .50 Cal machine gun cartridge works just fine. Improvise, adapt, overcome. This radio will also hear local AM voice radio transmitters like those used throughout WWII and beyond for military communications. If they are close enough, you don’t even have to tune the radio! They come in perfectly clearly. These Fox Hole Radios radios were undoubtedly used clandestinely in POW Camps by very brave people. If you had a Fox Hole Radio, you were the Go-To GI for the straight skinny; you actually KNEW what was going on.
A dog tag will also work instead of a blued razor blade but the blade seems to work better. Hmmm, I bet the blueing on that .45 caliber pistol magazine would work too. Semiconductor valence electron band-gap energy physics at work here. You need a high impedance earphone to convert the electrical signals to sound and the high impedance insures that the phones won’t load down the circuit. Eight ohm stereo phones or modern “ear buds” won’t work – but then again, they weren’t around in WWII…
The WWII Gillette company produced Blued razor blades for the war effort. Interestingly enough, if you look at one of those, it includes a small arrow printed on each side of the blade, ostensibly to indicate the way to insert it into the razor. (The blade used in this Fox Hole Radio was not made by Gillette).
Gillette manufactured these blades and then voluntarily magnetized them for use by POW’s as a field-expedient magnetic compass. When suspended by a thread, the arrow pointed North. (“The Escape Factory”, Reference 6). That would be politically incorrect in today’s “woke” Gillette.
Emergency Radio Receiver:
Since crystal radios have minimal parts and the ones required can be very small, it is possible to build a really small emergency radio. It compromises “tunability” for compact size and of course, no batteries required. Actually, the largest part is the plastic spool that the antenna is wound on. That spool contains 50 feet of #34 enameled wire for the antenna. The longer the antenna, the better! (If your antenna stayed up all winter, it’s not big enough). The earphone is larger than the radio “set”. See below
The basic circuit:
The above circuit is very simple. It consists of a parallel LC tuned circuit where the inductor is a 1/2 inch diameter toroid wound with about 55 turns of small gauge “Kynar” wire-wrap solid copper wire. Enamel insulated magnet wire will work fine as well. With this particular toroid, 55 turns produces about 12 microhenries. The antenna is connected to one end, ground to the other. The parallel “tuning” capacitor is a random 0.005 microfarad disc capacitor found in my scrap pile. A 1N34A germanium diode (anode) is connected to the antenna end of this parallel combination. A high impedance crystal earplug is connected between the diode cathode and ground.
Since these crystal earplugs look like a very high resistance in parallel with a capacitance, this capacitance will charge up to the peak diode voltage and then stop the earplug current flow. (Not an issue with high impedance magnetic earphones commonly used. Eg: The Heathkit CR-1) To prevent this, place a 47K resistor across the earplug to drain off this charge. The resistor costs a little signal but it’s necessary; value not critical. A potential gremlin, easy to overlook. (The Razor Blade foxhole radio did not need this discharge resistor. I believe the “reverse leakage current” back through the improvised diode effectively discharged the earphone capacitance through the coil).
The LC circuit is resonant at around 650 KC with these values but I used a “junk box” toroid with unknown permeability. Experiment with the toroid, number of turns and capacitor to see what you have and how many turns are required to get to the broadcast band. Nothing is particularly critical. Just make sure you use a germanium diode like a 1N34A due to its lower forward voltage drop as compared with a typical silicon diode (improves sensitivity for weak signals). “Tuning” is very broad due to the overall simplicity and design compromises to make it as small as possible. The LC ratio is not remotely optimum, circuit “Q” is unknown but it is simple, built with what I had, and it works! The internet is full of crystal radio circuits – explore and experiment! Last time I searched for “Crystal Radio” Google returned 63,000,000 results!
Below is the same radio after being “field-hardened” by inserting it inside some heat-shrink tubing to protect it. The diode and resistor are tucked inside the toroid “hole”. The yellow disc capacitor is visible. You can see the small size and this is perfect for keeping inside my pocket emergency kit. Mine is fixed-tuned at about 650 KC; you could build it to prefer any frequency but it is really “broad band” by nature.
In the San Francisco bay area I can clearly hear KGO, KCBS and KNBR (810, 740 and 680 KC respectively) during the day and primarily KGO and KNBR at night as some stations must reduce transmitter power at sunset. Operation is simple: Unwind the antenna wire and toss it up into a nearby tree with a small weight on the end. Keeping it vertical works best since the AM transmitters are vertically polarized but it works in any position. Of course, performance depends upon your proximity to AM radio stations, their power output, their frequency separation from each other, the length of your antenna and your ground connection etc.
The antenna is connected to the red wire, the black wire is connected to “ground” (however switching those connections works just fine). Ground could be a metal tent stake or a knife stuck into wet soil, another piece of wire laying on the ground, the proverbial “cold water pipe”, that barbed wire or chain link fence – anything metal in contact with the Planet. In regions where the ground conductivity is very poor (desert, rocks) you can cut the antenna wire in half and connect half to the red wire, the other half to the black wire making a dipole with the radio in the middle. That’s it. Stick in the earphone and you are in business. Plus, you don’t have to “turn it off” when you fall asleep!
Making it tunable is easy but that requires a rather large variable capacitor and “knob” and even in that case, it is still pretty broad in its tuning range. I chose to keep it small and simple and use my ear-brain to do the tuning. Actually it is pretty easy once you are “tuned in” to the specific program you want to listen to. To Tune in a different one, just change your concentration! Works better than it “sounds”.
You could make it completely waterproof (less the earphone) by squirting a small blob of clear silicone “liquid nails” or hot glue into the ends of the heat shrink tubing to fully encapsulate it. Simple, no-frills and effective with design tradeoffs to minimize complexity and size. Perfect for emergencies when everything is “out”.
Another fun exercise is to demonstrate these radios for your local youth groups. In that case, you can also have them play with the basic Foxhole Radio circuit but with using alternate detector materials rather than the razor blade or a germanium diode.
In the early days of crystal radios, galena (lead sulfide) crystals were found to be effective as a semiconductor when probed with the Cats Whisker. (I need a smaller Cat’s Whisker!)
Have the kids try various minerals from your handy-dandy minerals collection assortment or rocks they find locally. Some work, some won’t.
Crystal Radio Experiment with galena
Galena works well, or try iron pyrite (iron sulfide – or “fools gold”). That mineral also works.
Experimenting with crystal radio detector minerals
After connecting the mineral to the Foxhole Radio tuning coil, have the kids probe the surface of the mineral with one wire from the earphone. When they hear a radio station, eyes LIGHT UP! WOW! Fun.
Any future Engineer or Scientist worthy of the title will quickly reveal themselves via their ensuing curiosity.
©Brooke Clarke, N6GCE1800s Crystal Radio Description
A Crystal Radio by Brooke Clarke
Freed-Eismann Radio Speaker FE-50
Baldwin Speaker Driver
Heathkit CR-1
Dummy Antenna & Load
Related
A Crystal Radio by Brooke Clarke
Freed-Eismann Radio Speaker FE-50
Baldwin Speaker Driver
Heathkit CR-1
Dummy Antenna & Load
Related
Pat Pend adjustable Crystal assembly |
1800s Crystal Radio Description
I think this is a home made crystal radio (Wiki) from about 1800 (?). The 'Foote Phila. Pat Pend' is an assembly that has a Geltina crystal in a lead holder, but it has a threaded rod out the back. On the front panel there is a knob that turns a threaded rod with a Berrillium copper spring that can be adjusted so that it touches various spots on the crystal. I was able to adjust it for 2 volts and 0.9 volts (reverse and forward at 1 mA) using a Fluke 87 DMM.On the upperleft corner of the front panel is the ANTENNA connection. The bottom left terminal is GROUND.
On the right lower corner are the PHONES terminals (lower one is ground).
On the right lower corner are the PHONES terminals (lower one is ground).
The wire appears to be bailing wire or some other Iron wire, not copper.
The front panel terminals use an 8-32 threaded pinch screw with the threaded portion 5/16' long..
I'm looking for 3 of these.
I'm looking for 3 of these.
Circuit
From ANTENNA to PHONES is the diode.From ANTENNA to GROUND is a coil, where the upper 10 position switch sets coarse taps and the bottom 10 position switch sets fine taps.
From PHONES hot to PHONES ground is a 20 mmf capacitor that looks like a Copper bar with something wrapped around it and maybe some shim stock sandwidched between two thin wood boards.
Headphones
In the same lot as this radio there were two pair of headphones.
Federal Telephone and Telegraph Co., Buffalo, N.Y., U.S.A. Type 53-W, 2200 Ohms.
The other pair is marked with a 'M' on the center of the back and the number 1000 is stamped on the coil inside.
Federal Telephone and Telegraph Co., Buffalo, N.Y., U.S.A. Type 53-W, 2200 Ohms.
The other pair is marked with a 'M' on the center of the back and the number 1000 is stamped on the coil inside.
A Crystal Radio by Brooke Clarke
This radio was made in the late 1960s or early 1970s. This was during a time when I was spending a lot of time with the Boonton 160 Q meter and making a number of coils. The cardboard box has suffered from both the time and having stuff on top crush it.
With a 100 foot long wire this receiver picked up all the AM broadcast stations you would hear on a regular table radio. The best way to tune is first set the tank where the station will be then peak the antenna circuit. There's a small amount of interaction between the antenna circuit and the tank, but not a lot.
KGO, which is the San Francisco 50 kW clear channel station, would drive a loudspeaker so ear phones were not needed.
Freed-Eismann Radio Speaker FE-50
This speaker came with what I think is a nice Neutrodyne radio and a few battery eliminators. It's composed of a driver and an exponential horn. The driver is made by Dictograph (patent 1668509). It weighs about 15 ounces, you definitely would NOT use a pair of these for earphones, way too heavy. But that may be part of why it works so well. When used with the above crystal radio it provides enough volume from a strong station to hear on the opposite side of the room. Probably made under patents (see below): 1563500, 1621845 & 1668509 so probably made 1928 or later. The label on the back of the box reads:The Freed-Eismann Radio Speaker FR-50
caption under photo of speaker sitting on top of radio:
The NR-6 and the FE-50 Radio Speaker.
This Radio Speaker is equipped with a reproducing unit which does not require any adjustment at all. Do not under any circumstances tamper with the unit. The Radio Speaker should preferably be placed directly on top of your receiver as shown in the accompanying figure. In connecting up this Radio Speaker for the first time, it is important ot get the polarity of this Radio Speaker correct. Try the Radio Speaker with it's leads connected to the telephone plug (or the receiver binding posts) in one way, then disconnect and reverse the Radio Speaker leads. In one of these positions the signal may be clearer and louder than in the other. Leave the Radio Speaker permanently connected with the connetions giving best results. In the event you should ever obtain a persistent howl, it may be due to:
1- A defective detector tube.
2- Run down B Batteries.
3- Acoustic resonance.
Occasionally, if a Radio Speaker is placed in a small room or in a room in which the reflection of sound is very great, a sustained howling may be produced, and this may be overcome by separating the Radio Speaker from the receiver by putting a small piece of cardboard under the Radio Speaker to raise it from contact with the top cover of the cabinet, or it may be necessary to remove the Radio Speaker from the top of the set and put it on a table alongside the set. The guarantee on this Speaker does not hold if serial number of bottom of cabinet is in any way defaced.
FE50FreqResp.avi Video of frequency response. about 200 to 3000. Can hear 1 kHz with 80 mv input. DC resistance of input is 4 k Ohms. P = V*V /R = 0.08 * 0.08 / 4000 = 1.6E-6 watts or 1.6E-3 mW or 28 dB below 1 mw or close to 1 micro W.
An exponential horn (Wiki) is the best way to match free space to the driver.
caption under photo of speaker sitting on top of radio:
The NR-6 and the FE-50 Radio Speaker.
This Radio Speaker is equipped with a reproducing unit which does not require any adjustment at all. Do not under any circumstances tamper with the unit. The Radio Speaker should preferably be placed directly on top of your receiver as shown in the accompanying figure. In connecting up this Radio Speaker for the first time, it is important ot get the polarity of this Radio Speaker correct. Try the Radio Speaker with it's leads connected to the telephone plug (or the receiver binding posts) in one way, then disconnect and reverse the Radio Speaker leads. In one of these positions the signal may be clearer and louder than in the other. Leave the Radio Speaker permanently connected with the connetions giving best results. In the event you should ever obtain a persistent howl, it may be due to:
1- A defective detector tube.
2- Run down B Batteries.
3- Acoustic resonance.
Occasionally, if a Radio Speaker is placed in a small room or in a room in which the reflection of sound is very great, a sustained howling may be produced, and this may be overcome by separating the Radio Speaker from the receiver by putting a small piece of cardboard under the Radio Speaker to raise it from contact with the top cover of the cabinet, or it may be necessary to remove the Radio Speaker from the top of the set and put it on a table alongside the set. The guarantee on this Speaker does not hold if serial number of bottom of cabinet is in any way defaced.
FE50FreqResp.avi Video of frequency response. about 200 to 3000. Can hear 1 kHz with 80 mv input. DC resistance of input is 4 k Ohms. P = V*V /R = 0.08 * 0.08 / 4000 = 1.6E-6 watts or 1.6E-3 mW or 28 dB below 1 mw or close to 1 micro W.
An exponential horn (Wiki) is the best way to match free space to the driver.
331 s/n stamped in bottom wood in addition to the name plate s/n. | |
Dictograph Patents
967747 Transmitter Mouthpiece, O.F. Falk (Dictograph), Aug 16, 1910, 381/344 - better shape to transfer more sound energy1356634 Rheostat for Telephonic Insruments, Henry Koch (Dictograph), Oct 26 1920 - for hearing impaired users
1361590 Telephone Transmitter, Henry Koch (Dictograph), Dec 7, 1920, 379/428.01 ; 191/12.2R; 439/18; 439/30 - passenger to chauffeur
1372437 Telephone Switch Seperator, Henry Koch (Dictograph), Mar 22, 1921, 200/275 ; 200/1TK; 200/237; 379/325 -
stamping insulators for lever switches instead of turning them of screw machines.
1501670 Winding Machine, Henry Koch (Dictograph), Jul 15, 1924, 242/437.4 - Electromagnet Winding Machine 1501694 Signal System for Telephones and the Like, F.H.N. Wohlers (Dictograph), Ku; 15, 1924, 379/171 ; 340/825.41 - Intercom system
1545585 Extensible Cable Unit, Henry Koch (Dictograph), Jul 14, 1925, 191/12.2A
used for telephone cord boards to retract the cord or for a telephone cord between a wall and the phone
1545627 Cable Support, F.H.N. Wohlers (Dictograph), Jul 14, 1925, 200/61.14 ; 191/12.2A - used for telephone cord boards to retract the cord or for a telephone cord between a wall and the phone
1548325 Telephone Receiver, Henry Koch (Dictograph), Sug 2, 1925, 381/417 - strain relief looks like what's used for headphones1551722 Telephone Signal Device, F.H.N. Wohlers (Dictograph), Sep 1 1925,
379/102.07 ; 200/1TK - Intercom switch and indicator
Heathkit Radios For Sale
1551723 Transmitter, F.H.N. Wohlers (Dictograph), Sep 1 1925, 381/180 -
improved carbon ball transmitter where it can survive dropping. probably for passenger to chauffeur or Dictaphone use.
1563500 Loud Speaking Receiver Unit, Henry Koch (Dictograph), Dec 1 1925, 381/433 ; 381/411 - designed to fit the horn of a phonograph
copending application 628709
Has the appearance of this unit
1579369 Battery Carrier and Connector, Henry Koch (Dictograph), Apr 6, 1926, 429/99 ; 192/110R - Has the appearance of this unit
improved battery holder for a couple of 'F' (?) dry batteries. Prior art holders used flexable wrap and filler or could not be reused because the battery had gone dead and swollen up. Looks like the same batteries as used for the Moxley - Light Weight Railroad Lantern.
1621845 Loud Speaking Telephone Receiver, Henry Koch (Dictograph), Mar 22, 1927, 381/411 ; 381/340; 381/396 - Old Heathkit Radios
designed for use with radios where there is voltage and current in addition to the AC audio signal.
Also includes an extension of the knob to move it outside the speaker box.
shows the beginning of the horn.
looks like this unit, except for the knob extension.
1668509 Sound Reporducing Device, Henry Koch (Dictograph), May 1, 1928, application s/n 114888, 340/391.1 ; 381/396 - Also includes an extension of the knob to move it outside the speaker box.
shows the beginning of the horn.
looks like this unit, except for the knob extension.
On the back is a 'Patents Pending' and on the front is stamped, not cast like all the other markings, 'P33881' which must be a serial number.
1647182 Telephone Receiver, Henry Koch (Dictograph), Nov 1, 1927, 381/411 - air gap between diaphragm and pole pieces.Application s/n 674601 & co-pending applications 628709 & 661596 all for Loud Speaker improvements
Heathkit Cr-1 Crystal Radio Manual
2089402 Battery Holster, S. Murray (Dictograph), Aug 10, 1937 224/624 ; 182/3; 224/902; 224/930- for carrying hearing aid battery probably made from shoulder holster for revolver
2405433 Bone Conduction Audiphone, Henry Koch (Dictograph), Aug 6, 1946, 381/151 ; 381/417 - RE23125 Bone Conduction Hearing Aid, Henry Koch (Dictograph), Jun 21, 1949, 381/151 ; 335/231; 381/162; 381/378; 381/380
uses electromagnets to move plunger that transmits sound directly to the skull.
Dictograph has many many more patents, these were chosen as being in the approximate time frame as the Loud Speaker driver. They seem to have a number of very innovative patents just in this list.uses electromagnets to move plunger that transmits sound directly to the skull.
Baldwin Speaker Driver
The FE-50 speaker driver above does not use the lever arm type movement from the Sound Powered Telephones, but it still has great sensitivity.
I got this after studying Sound Powered Telephones and the very efficient speaker elements they used. This speaker driver uses a similar if not the same drive method.
I got this after studying Sound Powered Telephones and the very efficient speaker elements they used. This speaker driver uses a similar if not the same drive method.
Both of the below patents cover the
957403Telephone-receiver, Nathaniel Baldwin, May 10, 1910, 381/418 -
1604251Telephone receiver, Nathaniel Baldwin, Oct 26, 1926, 381/418; 381/419 -
1604251Telephone receiver, Nathaniel Baldwin, Oct 26, 1926, 381/418; 381/419 -
Heathkit CR-1
Trying to understand dummy antennas to allow testing this radio and the other crystal radios.
Dummy Antenna & Load
Dummy Antenna
The IRE Dummy antenna can be made using a series 15 Ohm resistor and 20 uH coil between the signal generator and antenna terminal on the radio.A 10 Ohm resistor between the signal generator ground and radio ground that can be used to measure the input current (for calculating input impedance).
In Wireless Age Oct 1922 pg 68:
400 pf series cap, 25 Ohm series resistor, 28 uH series inductance.
RMA Dummy Ant:
Signal gen hot - parallel circuit [ one leg 20 uH, other leg 400 pf in series with 400 Ohms] then 200 pf in series - radio ant terminal
Signal gen gnd - radio gnd.
Dummy Headphones
2000 Ohm resistor (optionally bypassed with 0.01 uF)Related
Crystal Radios - general info & Q of coils
Crystal Clear: Volume 1 by Maurice L. Sievers
Crystal Clear: Vintage American Crystal Sets, Crystal Detectors, and Crystals: Volume 2 by Maurice L. Sievers;
crystal-radio.eu -
One Tube Raio - Lee De Forest patent preceeded the Armstrong patent
Crystal Clear: Volume 1 by Maurice L. Sievers
Crystal Clear: Vintage American Crystal Sets, Crystal Detectors, and Crystals: Volume 2 by Maurice L. Sievers;
crystal-radio.eu -
One Tube Raio - Lee De Forest patent preceeded the Armstrong patent
Links
The Xtal Set Society -
Wiki: Crystal radio
Gollum´s Crystal Receiver World - Crystal Set Testing
Crystal Radio section on Brooke's Electronics web page.
crystal-radio.eu -
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page created 17 Nov 2001.