Don has it right, but it depends upon how new the D-104 is. The versions made the last 20 years or so, using the same D-104 high-impedance crystal element we hooked to our tube transmitters half a century back, now has a transistor amplifier/impedance matching unit in the base. If your unit has a base plate in the stand that takes a battery, you have one of the newer units designed for modern rigs.
The schematic of the D-104 amplifier and a nice graph of what a great communications microphone frequency response curve looks like are at the Astatic site: http://www.astatic.com/cb/d104.htm It should be pretty simple to duplicate if you have one of the older mics. Just about any NPN transistor can be used (2N2222, etc). Ron AC7AC -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of W3FPR - Don Wilhelm Sent: Tuesday, September 27, 2005 5:13 PM To: [EMAIL PROTECTED]; elecraft@mailman.qth.net Subject: RE: [Elecraft] D 104 mic with K2 The D 104 mic (unamplified version) needs to look into a very high impedance (50k ohms or greater). That mic was developed in the days of vacuum tubes with mic amplifier input inpedances in the 50k to 1 megohm range. Modern transceivers present an impedance of something close ot 600 ohms at the mic input jack, so to properly use a D 104 with modern transceivers, you will need an amplifier stage - the gain can be low, but the input impedance must be very high and the design output impedance should be in the vicinity of 600 ohms. A few circuits to do that have been published in QST over the past 2 or 3 years. Sorry, but I don't have a specific issue reference. I took a different route with my D 104, I put a Heil HC-5 element in the D 104 head - it works FB, but the Heil elements need about 3 to 6 dB of gain to properly drive the K2, so a preamp stage is still needed (or the KI6WX increased gain mod of the KSB2 - which is what I use). 73, Don W3FPR _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
