[AMRadio] Mike

StephenTetorka at cs.com StephenTetorka at cs.com
Tue Mar 15 09:24:50 EST 2005

Thanks Guys:

This mike is for a vintage 1948 AM rack rig homebrew by W2PLY who moved into Senior Residence.
The speech amplifier/modulator schematic is right from August 1947 QST.

I got the rack and the 5 sections directly from the flat bed trailer at the estate sale...and now just about finished doing what very little fixin required.

The article cites a crystal mike; it feeds directly into the grid of a 6SJ7 with no grid leak resistor.

As I understand these things, the mike - what type of cartridge - needs to put out 'so many' microvolts necessary for the tube into which it feeds.

And the impedance needs to 'match'.

I understand there plenty of gain after the 6SJ7...and one of the 6SN7's has a "tone control" potentiometer in the grid.

Personally, my voice is a little higher from center in pitch..and I'd prefer more lower than higher freq. response...which is generally a problem due to low freq. rolloff in the mike curves...that's why I'm eager to try this 'tone control'.

I guess the first question is: what impedance number is required for a 6SJ7 grid?

Your generous help is always appreciated.


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