[Milsurplus] Navy 5-wire handsets

Sun Jul 11 17:32:17 EDT 2021

I don't  know much about the URC-9 other then it is a derivative of the VRC-24 and by extension, the TRC-68.  I worked on the TRC-68 some 50 years ago.  My URC-9 manual went to Danial a few weeks ago along with a URC-9 R/T unit.  I have been using the VRC-24 / TRC-68 manual pdf found online so I am having some trouble following circuit connections that disappear from time to time as I follow it over two pages of schematics.  
There is a J15 on the mainframe which connects to a jumper plug P2 which can be inserted into J15 in one of two ways.  One configures the R/T unit as a VRC-24 and when inserted the other way configures the R/T unit as a TRC-68.  I suspect that some of this re-configuration is due to the use of either a dynamotor in the VRC-24 or the AC power supply in the TRC-68.  
In the VRC-24 configuration, -30 volts is applied to the microphone input line via R-817 (150 0hms) and R-604 (1k) from the -30 volts from the dynamotor.  It could very well be -12 volts when the microphone is keyed but I haven't bothered to calculate voltage drops.  
I assume that the TRC-68 is the same but that the -30 volts is supplied from the AC power supply.  Not really sure since I again have this problem of tracing lines that become transparent in places over two fold out pages of schematics.  If there is a J15 on the URC-9 main frame then I am quite confident that there is no difference between the VRC-24 / TRC-68 and the URC-9 other then a new metal casting of the front panel.
So I don't see where +12 volts is available in the URC-9, there should only be heater voltages, +125 VDC, +300 VDC and -30 VDC bias.  Or do I need a better schematic?Jim
Too much agreement kills a chat.  E. Cleaver

-----Original Message-----
From: Nick England <navy.radio at gmail.com>
To: Jim Whartenby <old_radio at aol.com>
Sent: Sun, Jul 11, 2021 11:46 am
Subject: Re: [Milsurplus] Navy 5-wire handsets

Not that I have found. Instructions for repair were “discard and replace entire mic cartridge”. 
On Sun, Jul 11, 2021 at 12:37 PM Jim Whartenby via Milsurplus <milsurplus at mailman.qth.net> wrote:

NickDoes a "proper" schematic for the H-169/U exist?  
Jim

Too much agreement kills a chat.  E. Cleaver

-----Original Message-----
From: Nick England <navy.radio at gmail.com>
To: Jim Whartenby <old_radio at aol.com>
Sent: Sun, Jul 11, 2021 7:39 am
Subject: Re: [Milsurplus] Navy 5-wire handsets

No reference to switching element leads.Nick. 
On Sun, Jul 11, 2021 at 8:34 AM Nick England <navy.radio at gmail.com> wrote:

Now I am even more puzzled!In the transmitter Pin D is ground and pin C is the audio line (-12v through xfmr primary). 

On Sun, Jul 11, 2021 at 1:53 AM Jim Whartenby via Milsurplus <milsurplus at mailman.qth.net> wrote:

Nick and Danial
Here is the schematic I made of the H-169/U perhaps 15 years ago when I reworked W5OR's URC-32s.  I couldn't find any marking on the NPN transistor and the capacitor on it's base is perhaps 27 uF, can't read my own handwriting, 77 uF doesn't sound right!  Don't remember if I calculated the voltages shown or measured them.
It looks like the diode is there to prevent a reverse bias condition.  Perhaps there is an obscure reference to reverse the connections to the circuit board underneath the microphone element or in the connector for use with some equipment?
Enjoy!,Jim

Too much agreement kills a chat.  E. Cleaver

-----Original Message-----
From: Daniel Jones <djones at k6yic.com>
To: Nick England <navy.radio at gmail.com>
Cc: Milsurplus at mailman.qth.net
Sent: Sat, Jul 10, 2021 9:03 pm
Subject: Re: [Milsurplus] Navy 5-wire handsets

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…..
DanielK6YIC 

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.JPGThe 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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-- 
Nick England K4NYW
www.navy-radio.com

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