By David - K3DAV
First let's cover a little history of the Astatic Microphone and it's brilliant inventors.
In 1930, a couple of ham radio operators named, Creed Chorpening, W8WR (later W8MJM), and F.H. Woodworth, W8AHW, were trying to come up with microphones that had the quality necessary for their ham radios. They had a friend named Charles Semple. Semple had been experimenting with Rochelle salt crystals. Semple demonstrated some crystal pick-ups, Chorpening and Woodworth both recognized that the crystal microphones provided excellent quality audio and would be perfect for use on their ham radios. As a result, Chorpening and Woodworth created and opened "The Astatic Microphone Laboratory, Inc." in Youngstown, Ohio in 1933. Semple was hired as general manager to manufacture and market the first line of D-104 Crystal Microphones. They soon came out with a complete line of crystal microphones, followed by crystal phonograph pickups and recording heads for manufacturers of commercial tape recording equipment.
In 1944, Astatic moved their operations to Conneaut, Ohio. During World War II, Astatic designed, and manufactured several kinds of electronic equipment. They included, under-water sound detection or Sonar devices, and hydrophones for the U.S. Navy under direct contract. Astatic perfected and produced a Static Discharger for dissipating static electricity which accumulated, due to friction in flight, on wing surfaces, fuselage and tail assemblies. Astatic also designed and manufactured coaxial cable connectors that were used exclusively by both the US Army and US Navy for Radio, Radar and Sonar connections.
After World War II, Astatic Microphone Laboratory became The Astatic Corporation. Currently, the company is located in Solon, Ohio and offers microphones and audio accessories to the professional, commercial, and installation audio industries. The Amateur & CB product division of Astatic was sold to Barjan, LLC, a major mobile communications product distributor.
Introduced in 1933, the Astatic model D-104 was popular for its high frequency response which resulted in very intelligible audio.
The original D-104 was the stand with the famous Astatic "Grip-to-talk" key bar down the side of the neck. It only used the crystal mic element without an amplifier. Its high output voltage, which was characteristic of crystal elements, and its high impedance (50,000 to 100,000 ohms), allowed for direct grid input to older tube radios. The "Grip-to-talk" switch stand ("G" Stand) was introduced in January 1938 but didn't become popular until much later. The D-104 continued in production with little change until the 1960s when a solid-state amplifier was added to the "G" stand. In 1976, an eagle and shield was added to the rear cover to commemorate the US Bicentennial. Other variations appeared from time to time such as...
They are all the same exact microphone using the same crystal element, same key switch, and the same 2 transistor preamp in the base. Only the outside shell was painted differently to appeal to the tastes of millions of Amateur and CB radio operators worldwide. My favorite is still the D-104 Special, aka "The Black Special. I still have mine and it is working fine.
The "G" Stand stood for Grip to talk switching in the neck. The "UG" Stand was later known as the "Universal Grip" switching. The "TUG" Stand is for "Transistorized Universal Grip" stand when Astatic added the preamp in the base. The "TUP" is for the Transistorized Universal Push" stand after they added a bar on the base that could be pushed down to transmit. The bar changed how the electronic switch was made. The old G, UG, and TUG stands had the actual switch in the neck. The top of the side mounted bar pushed in on the switch to activate it. When Astatic added the push bar in the base, a new switching device was invented to replace the switch in the neck. The switch was now located on the preamp board in the base, and the base bar pushed down on it to activate it. The side grip bar now has a mechanical rod in the neck that pushes down on the base bar internally.
Astatic later made the D-104M6B. A hand held mic for mobile use. It did not use the famous crystal mic element. It used a dynamic element that rivaled the quality of the original D-104. That was due in part to the FET transistor preamp inside. The M6B is probably the best sounding hand mic anywhere.
Sadly enough, an era had ended when Astatic ceased production of the D-104 forever in 2001, 68 years after the original D-104 was made. The D-104 was always, and still is an icon of quality radio audio. It is a status symbol of pride and prestige when displayed on or near the operators radio equipment. But there are still hundreds of thousands of D-104 mics still in use today. I still use my Black Special on my Icom 706MKIIG.
For use on many of today's ham radios, a small modification needs to be made to the D-104. Some Ham Radio manufacturers design their mic audio circuits to use the higher outputs of Electret Condenser mic elements. Electret's have an FET transistor built into them as a preamp. That little transistor needs power to make it work. So the radio manufacturers insert 7.5 volts DC directly onto the audio wire to power the Electret element. The 7.5VDC from the radio will not hurt the D-104 amp. The amp circuit design has a capacitor on the output side that blocks the voltage on the audio line from the radio. So that it not an issue to worry about.
The D-104 has a much higher audio output level than any electret element. This problem can be solved with one little resistor in the mic. Take the bottom off the D-104, and locate the WHITE wire from the coiled mic cable. Unsolder the white wire from the tab or the amp board. Insert a 33,000 ohm resistor in the audio line. The color code for a 33,000 ohm resistor is 3 orange stripes on the resistor. Solder one side of the resistor to the point on the tab or amp board where the white wire WAS soldered. Then solder the white wire to the other side of the resistor. Wrap a little electrical tape around the solder point where the white wire is connected to the resistor to prevent the wire from shorting out against the bottom plate or any other point in the mic. Then put the bottom back on. The resistor simply cuts back the high output of the D-104 preamp.
Leave the audio level control on the bottom of the D-104 turned all the way down, (Fully counterclockwise). Turn the mic gain control on the radio to the half way point. Put the radio into either one of the SSB modes. As you key-up the D-104, start turning up the audio level gain control on the D-104 and speak normally about 4 or 5 inches away from the mic element until the power meter starts to hit it's peak power most of the time, but not all of the time. Then stop adjusting, and do not touch the level control on the D-104 again. If you ever need to increas your audio, only use the radio's mic gain control to add what your need. When the right audio level is found, you will be surprised at the quality of audio the D-104 can produce. Especially on FM. And SSB audio will be clean and strong enough to drive the finals to full power without distortion.
NOTE: The 7.5 VDC that some manufacturers insert directly onto the audio line, will not power the D-104 at all. The battery or another power source is still required to power the D-104 amp. Continue reading below for an alternative power source to eliminate the battery.
Battery Elimination Modification
This modification is only for ham radios and will not work with CB or illegal Export CB radios.
Most ham radios have one pin on the mic jack that is used exclusively to provide 8VDC at around 5 to 10 milliamps. This 8VDC is provided to trigger relays, or low current power for any external device that may require it. Check your radio's owners manual to find the correct pin number that carries the 8VDC. Different brand name radios use a different pin number for this purpose.
This 8VDC pin has more than enough power to run the pre-amp board in the D-104. Unplug the D-104 from your radio, remove the bottom plate and remove the battery from the D-104. You can use any unused wire in the D-104 mic cord such as the YELLOW wire. At the mic plug end, solder the yellow wire to the correct pin that provides the 8VDC from the radio.
Now inside the D-104, solder the yellow wire to the same spot on the amp board where the (+ RED) wire from the battery clip is soldered. Then wrap some electrical tape around the battery clip to make sure it does not touch anything in the mic. There is no need to add a ground wire to the battery clip as the D-104 amp is already grounded to the radio through the audio shield wire. Only the 8VDC wire is necessary.
You are done. Put the bottom plate back on the D-104 and operate as usual. The 8VDC will now replace the battery and power the pre-amp in the D-104.
If you have any questions about this article and D-104 mics, please feel free to email me at firstname.lastname@example.org