[Boatanchors] D-104 mic

[Gary Schafer]

Years ago I went thru changing 3 different D-104 cartridges as it looked
like they were all bad. 
The transmitter would work fine with a dynamic mike but would not work with
the D-104. So it appeared that the cartridge was bad. After the 3rd one I
dug a little deeper and found that the first speech amp tube was leaky. With
the high impedance D-104 the tube had enough leakage to bias itself into
full conduction and saturation. With the dynamic mike there was a DC ground
on the grid via the mike element and the leakage did not show up.
Put a new tube in and the D-104s worked fine.

73
Gary  K4FMX

> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> bounces at mailman.qth.net] On Behalf Of telegrapher at q.com
> Sent: Monday, July 18, 2011 3:51 PM
> To: boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] D-104 mic
> 
> I feel i have determined that two of the heads are bad.  I have a 3rd D-
> 104 that i use with my TCM equipment and supplies plenty of drive for
> it.  Apparently it sounds good also as i've had extremely good signal
> reports, audio quality wise.  I swapped the heads around and found two
> of them that were putting out nothing.  Even the old VOM and listen for
> a click routine showed no results.  they both measure wide open and that
> apparently from what i have been told is correct.  The wiring from the
> heads clear into the radio thru the G stands checks out with no grounds
> nor opens.  I ahve ordered three (3) of the Kobitone elements from
> Mouser.  The third of course is in the event the now working mic goes
> belly up.
> 
> I have other Mics as well, an Apple electret mic, one from a Sony Tape
> deck and an Astatic "Cardinal" that is still in it's original box and
> looks unused.  The Sony mic gives the highest modulation indication on
> the transmitter.  I've not listened to it in an "on the air check" so i
> don't know as yet how it sounds.
> 
> We can now end the thread as i am buying the Kobitone elements.  Thanks
> to all for the input and comments.
> 
> larry
> W0OGH
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