[Milsurplus] Navy 5-wire handsets

[Daniel Jones]

I too am interested in this topic as I am dealing with this issue on a URC-9.   Nick was nice enough to supply a good handset but why the unusual change in polarity?  

Plus on the flip side I am only dealing with a URC-9 set, I wouldn’t mind messing around with a SRT-14 should anyone have on excess to there needs on the west coast…..

Daniel
K6YIC 

Sent from my iPhone

> On Jul 10, 2021, at 18:48, Nick England <navy.radio at gmail.com> wrote:
> 
> 
> 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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