K3 MIC BIAS

[Bill N2BC]

What are the I and E ratings of the K3's pin 6 "BIAS" ?

THX!   73, Bill  N2BC
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[Brett Howard]

Looks like that is hanging off of the TPIC6C595D on page 19 of the
schematic.  The TPIC6C595D is a shift register that has 100mA of continuous
current handling capability.  Looks like its power is hooked to VCC5 I'd
guess that's 5V.  

Keep in mind this is a very on-official answer but being that Elecraft posts
all of their schematics why not dig in and help out...

~Brett (KC7OTG)

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Bill Coleman N2BC
Sent: Tuesday, January 22, 2008 3:27 PM
To: [hidden email]
Subject: [Elecraft] K3 MIC BIAS

What are the I and E ratings of the K3's pin 6 "BIAS" ?

THX!   73, Bill  N2BC
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[Brett Howard]

Just at a further note I found this comment on some MFJ microphone control
nugget...

Also, Kenwood microphone specifications call for +8 VDC on the microphone,
while Alinco radio specifications call for +5 VDC on the microphone.
Therefore, the audio from the Kenwood microphone to the Alinco radio may be
a little weak due to the low bias voltage.

Maybe that shift register is buffered....

Upon further review there is a buffer.  It’s a MMBT3906 which has VCC8A on
the top (I'll bet a dollar that’s 8Volts).  The general description on the
part from Fairchild is: "This device is designed for general purpose
amplifier and switching applications at collector currents of 10 µA to 100
mA."

The datasheet says the Ic is 200mA Continuous.  Here is a link to it:
http://www.fairchildsemi.com/ds/MM/MMBT3906.pdf

That signal seems to run all over the place... :)  The part with the 8V on
it is on page 10 (Q9).  There is also a UA78M08CDC (U28) that looks like a
linear regulator that goes to that signal that I'm not easily finding a
datasheet for...

Sorry for the previous mis-information but I'd bet its 8V.  I think the
schematic will make more sense once I actually get to see how the boards
plug together.


-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Bill Coleman N2BC
Sent: Tuesday, January 22, 2008 3:27 PM
To: [hidden email]
Subject: [Elecraft] K3 MIC BIAS

What are the I and E ratings of the K3's pin 6 "BIAS" ?

THX!   73, Bill  N2BC
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