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Are you talking about a D-104 element? If so it should measure open circuit for DC. It should look like a capacitor. If you are getting resistance it is defective or else you are measuring something else.
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Note that the bass roll off of the D-104 is not entirely due to its impedance. These were meant to be voice range mics with a fairly sharp peak at 3Khz and a roll off below about 1 Khz. The D-104 was the first crystal mic to be available commericially, c.1933. Initially there were two versions, the peaked voice version and a flat version. The flat version was not made for long but Astatic and others have made plenty of flat crystal mics. The load impedance affects mostly the bass roll off, not the HF peak. The peak is a result of mechanical and acoustic resonances built into the mic, it is a feature not a fault. Unless there is something else in the mic a resistance in a crystal mic is an indication that the element is damaged. The value Steve reports sounds like perhaps an electret whre an active element is being measured. It is the wrong value for a high impedance moving coil mic. On 2/3/2025 9:04 AM, Ralph Mowery via groups.io wrote:
Attached is a file I have on the amplified d104 --
Richard Knoppow Los Angeles WB6KBL SKCC 19998 |
