Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang ---------------------------------------------------------------------- Eddy -
The mic amplifier came about primarily because of the solid-state transmitter. The D-104 and other similar mic's were designed to drive very high input impedance (i.e., tube) mic amplifiers, typically 500 k ohms. These mics generated several volts of audio at these impedance levels with no additional amplification. Solid state amps, on the other hand, had input impedances of 500 ohms or so, and these mics were unable to drive them. So some mic manufacturers installed amplifiers, not so much for gain, but to allow them to drive low impedance loads. A secondary effect was that the "bare" mic's frequency response was highly dependent upon the actual load impedance, and of course the internal amplifier was able to reflect an "ideal" load for the mic element.
So the amplifier was a good solution all around. The gain control allowed the amplified mic to drive BOTH the low impedance radios at the relatively low level needed (typically hundreds of millivolts) AND the high impedance radios at the high level needed (typically a volt or more) simply by adjusting the gain. The constant input impedance of the internal preamp allowed the mic element itself to have a constant frequency response regardless of the radio it was connected to.
You can either use the amplifier or not, as long as you adjust the preamp control correctly. Bypassing the preamp completely is one option, and the input impedance of the T-4X results in a good frequency response from the D-104. Depending upon your voice characteristics, you might want to add a resistor in series with the mic input to tailor the response somewhat. If you leave the preamp in place, you can set the mic gain appropriately by setting the GAIN control on the T-4X to about 10-11 o'clock, and then adjusting the preamp control so that normal speech kicks the Plate meter to about 100 - 150 mA on peaks.
73, Garey - K4OAH Glen Allen, VA Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs <www.k4oah.com>
Hi Dan, Sounds like "...sound advice" (pun intended!) to me... I shall do exactly that, probably later to-day. Thanks for the note, & my vy ~73!~ Eddy VE3CUI - VE3XZ PS: Were these amplified D-104 mics some sorta hang-over from the old "...louder-is-better" CB days...?!
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