All of the vacuum tube rigs from the 50's that I used with a D-104 had an input impedance of between 500k Ohms and 1 Megohm (the grid resistor of the first speech amplifier stage). Astatic does not list a specific load impedance on the specifications sheet I have.
The original D-104 used a Rochelle Salts crystal element which was very sensitive to fracturing from a jolt (don't drop!) and was hydroscopic, which made the life of the element dependent upon the hermetic seal and careful handling. Many of those seals leaked over time which destroyed the element. Later Astatic switched to ceramic elements (like most other mic manufacturers selling Rochelle Salts crystal elements). Ceramic elements are not sensitive to moisture in the air, more resistant to mechanical abuse and still have decent output and a fairly high impedance, which made them popular with owners of rigs designed for crystal mics. One of the enduring features of the D-104 that was certainly responsible for much of its popularity was its frequency response. It was carefully shaped for optimum communications speech. That was critically important back in the days before aggressive speech processing in Ham rigs. The frequency response of even "high end" rigs was solely limited by the selection of coupling capacitors in the speech amp and, perhaps, the modulation transformer, so a well-designed response in the mic made a huge difference. The D-104 mic specifications show this frequency response: 100 Hz, -10 dB 200 Hz, -3 dB 1 KHz, 0 dB 2 kHz, +8 dB 3 KHz, +12 dB 5 kHz, -2 dB 6 kHz, -11 dB 10 kHz, -18 dB Our modern rigs have a frequency response that is almost completely defined by the filters in the SSB generator - at least from a couple hundred Hz to between 2 and 3 kHz. So you can throw away any values outside that frequency range in the above table. What's left is a rising frequency characteristic, which is normally good for communications. If it rises too much when the D-104 is used with the K3, it should be easy to bring it under control with the transmitter equalizer. Considering the K3's design to accommodate low-output mics, I'd be astonished if an external preamp or impedance matching system was required. Ron AC7AC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
