Ron, My first reply bounced so here it is again. --------------------------------------------------------------------- Ron, On their Web page, Astatic does not give the value of the Base to Collector resistor value in the first stage of the the preamp but they do for the same resistor in the second stage. Have you any idea what it might be?
On 9/27/05, Ron D'Eau Claire <[EMAIL PROTECTED]> wrote: > > 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 > -- John [K7SVV]
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