[Milsurplus] Navy 5-wire handsets

[Nick England]

Looking at post-WW2 transmitters and handsets:
The SRT-14 and URT-2 series of AM transmitters supply -12V through a xfmr
primary to pin C for a carbon mic to ground (pin D) in the standard Navy
Type 51007 handset
The URC-32 SSB xcvr does the same.
BUT...
The URC-9 supplies +12v through the xfmr primary to pin C
The T-827 exciter for WRC-1, URT-23, etc also supplies +12v

Polarity obviously doesn't matter with a carbon mic in the handset, BUT....
in 1960, the standard 51007 handset was updated to 51007A by replacing the
carbon mic cartridge with a noise-cancelling cartridge with dynamic mic
plus transistor amp.
https://www.navy-radio.com/xmtrs/handsets/handset-51007a-spec-11.JPG
The ubiquitous H-169 handset replaced the 51007 and has the same circuit.

So why does the transistorized mic work with both + and - supplies?
In addition to cautions to respect polarity, the mic cartridges in these
handsets are marked + and - with - going to pin C.
OK, you can put in a diode bridge so that either polarity will work, but
then why the caution about respecting polarity? The 51007-A field change
does say that the new mic cartridge includes protective circuitry in the
event of reverse polarity but still cautions that it must be operated with
correct polarity....
" The transistor preamplifier is operated from the negative 12 volt d.c.
power normally supplied from the associated control unit or transmitter.
The circuitry contains protective provisions in the event of the
application of 12 volts direct current with a reverse polarity. When a unit
becomes defective, it must first be assured that a 12-volt direct current
of proper polarity has been applied; and if so, the unit must be discarded."

I seem to missing something somewhere. O exalted ones, this poor
grasshopper seeks enlightenment........

Cheers,
Nick England K4NYW
www.navy-radio.com
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