A 1960’s Astatic D-104 Mic in the 21’st century – a real baby boomer

I made a pass through my basement to see what “valuable radio artifacts” (some call it junk) I could unearth.  I discovered a couple of Astatic D-104 Microphones.  (See more old Mics).  These Mics were made a long time ago and Astatic has a rich history going  back to 1933.

Here is a bit of history from the Wikipedia on Astatic and the D-104

Introduced in 1933, the Astatic model D-104 was popular for its high frequency response which resulted in very intelligible audio.

Its high output voltage was characteristic of crystal elements and its high impedance allowed for direct grid input. The early D-104 mikes used a 1″ thick case and have a large ID tag along with tapped holes for “ring & spring” mounts. The case thickness was reduced in April 1937 and smaller tags were then used and the ring holes eliminated. The “grip” switch stand (“G” Stand) was introduced in January 1938 but didn’t become popular until much later. The early “G” stand bases were gloss black with metal ID tag.

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 until 2001, when production ceased, 68 years after the first D-104 was offered. [4]

The D-104 is often used by CB radio hobbyists and vintage amateur radio enthusiasts as part of their operating activities.

I bought the D-104’s about 5 years ago for use with my collection of vintage Kenwood (see them) and Heathkit (see them) radios.

It Worked the last time I used it !!

Once unearthed I found that one of the D-104’s worked and one did not.  “It worked that last time I used it” is a familiar phrase well known by all  who attend hamfests or flea markets.  At a hamfest or flea market the seller wants to dispose of items in the most expedient way possible.  To say that it worked the last time they used it is a good use of plausibility deniability for the seller (but bad for you the buyer).  If you’re a seller, don’t test the item.  Ignorance is bliss… and this blissful strategy could make a fast sale.  If you are a buyer, don’t forget to ask the seller about the 30/30 guarantee – 30 feet or 30 seconds.  Doubtful you will get any more than this.

But, both D-104’s really did work that last time I used it.  Really, no kidding. So I have plans for both of these D-104 microphones.  Use one.  Gut one and find out why it doesn’t work – (stay tuned for a posting on this)

The D-104 on a modern radio – the Yaesu FT-7800

The Astatic D-104 was designed in the age of tube radios which require a high impedance microphone.  High impedance is usually 5,000 – 10,000 ohms.  Modern solid state radios generally want a microphone of about 600 ohms impedance.

Would the Astatic D-104’s work with my modern Yaesu FT-7800 dual band VHF/UHF radio?   (read my review of this radio)

Nothing like giving it a try.

Spit and Bailing Wire

Since I was not sure if it would work I jury rigged a setup using a terminal strip, alligator clips, a telephone extension cable, and some paper clips.  It took about 10 minutes to set this up.

On the FT-7800 side…

The FT-7800 uses a modular 6-conductor cable to connect the Mic to the radio.  This is also known as a 6-conductor telephone extension cable.  You can get this at Wal-Mart for a few dollars.  I already had one on-hand which just encouraged me more to do this experiment.  I cut the 6 foot cable in half.  Stripped the wires and attached then to one side of the terminal strip. The D-104 connections would be on the other side.

On the Astatic D-104 side…

Since I did not want to mess with the 4 pin Mic connector already on the Astatic D-104 (wired for my vintage Kenwood radio’s) I found that a bent paper clip fit nicely into the attached Mic plug.  Attaching alligator clips to the paper clips would allow me to easily experiment with different connections to the terminal strip

Making the connections of the FT-7800 to the Astatic D-104

I got a Mic writing diagram from the FT-7800 manual.  It couldn’t be easier to feed audio into the Yaesu FT-7800 and key the radio.  It only takes three connections.  On the FT-7800 Pins 6,5, and 4 are PTT, Mic, and Ground respectively.  Short PPT (6) to Ground (4) to key the radio.  Feed Audio into Pin 5.  That’s it.  Simple.

You can see the connections below and some notes.

So, what’s the bottom line

Before I hooked up the Astatic D-104 power mic people told me I had “low audio” on my Yaesu FT-7800 using the stock mic.  Using the D-104 on the Yaesu FT-7800 made a world of difference.  On-air reports told me to “turn it down”.  One person told me that listening to the D-104’s he thought he was required to “stand at attention” – now hear this.  Very loud.  I was able to adjust the Mic gain of this amplified Astatic D-104 with the help of several on-air personalities on a local repeater.

So, A++ for the 1960’s Astatic D-104 on the Yaesu FT-7800.  It really is a  “boomer” from the 1960’s.  Even though it’s a high impedance mic in a low impedance world of modern radios it works very well “as is”.

Perhaps if you have a D-104 resting somewhere try it on a modern radio.  My results were unexpectedly great.

Resources

Notes

1. There are a number of versions of the Astatic D-104.  Some are amplified and some are not.  Some have five conductors in the Mic cord and some have three conductors.  Both of my D-104’s are amplified with 3 conductors (Mic(White), Black, Red, and Shield).  Shield is ground which is also chassis ground on the D-104
2. The Ft-7800 provides +9v on pin 3.  You might be temped to use this to power the D-104.  Not sure that is a good idea – more on this later.
3. On the inside of the D-104 there is a slide switch.  One side is marked E and the other side is marked R.  Despite what you might hear from CB folks these do not stand for E(cho) and R(everb).  They stand for Relay and Electronic.  In the R position pressing  PTT connects Red and Black (as in “relay” connection).   In the E mode when the PTT is pushed Red is pulled to ground; otherwise Black is pulled to ground.  In the setup below, the switch is set to E and the Red wire is connected to the FT-7800’s PTT Pin(6).  Pushing PTT on the D-104 takes pin 6 to ground and keys the FT-7800.
4. With the gain set to 3/4 on the D-104 on-air reports say that’s as loud as they can stand.

Here is the setup.  Click to enlarge.  Note the Mic Wiring diagram on the sheet.  The FT-7800 uses a 6 pin modular plug (NOT an RJ-45).  Although more than three connections are made to the terminal strip on the FT-7800 side only three connections are needed – Audio in, PTT, and Ground.  Pin 3 (red wire) is +9V from the radio (measured as 8.9V).  One would be tempted to use this to power the D-104 thus eliminating the need for the 9v battery in the base.

More stuff

https://frrl.files.wordpress.com/2012/01/adapting-the-astatic-d104-mic.pdf

History of Astatic – http://www.west-techservices.com/p15.htm

Try it on the ICOM 706-MKIIG – http://www.qsl.net/w8cwe/d104/d104.html

Mic connections and manuals for lots of radios – http://www.qsl.net/g4wpw/date.html