[AMRadio] Mike

Ed Sieb (E-mail) esieb at sympatico.ca
Tue Mar 15 10:51:26 EST 2005

Hi Steve,

What's the finals on that rig, 813's?  I  think I have a rig just like that
Can you describe the rig?  Is a schematic available?




> -----Original Message-----
> From: amradio-bounces at mailman.qth.net
> [mailto:amradio-bounces at mailman.qth.net]On Behalf Of
> StephenTetorka at cs.com
> Sent: Tuesday, March 15, 2005 9:25 AM
> To: amradio at mailman.qth.net
> Subject: [AMRadio] Mike
> 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.
> Regards,
> Steve
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