[MRCA] GRC-106 Pin J

Sat Sep 3 21:59:43 EDT 2016

Gang,

I don't know much about the 106, but, as someone pointed out verbally, 
the the 50-ohm (carbon) mic input, pin 17, hits a 10:1 voltage divider 
before it joins up with the 600-ohm input, pin 16, at test point J1.  In 
other wards the carbon mic input is attenuated 20 dB.  Looks to me like 
they were anticipating supporting dynamic mics in some application.

Figure FO-18, page 634 of the TM 11-5820-520-34 PDF from radio Nerds.  
http://www.radionerds.com/images/4/4e/TM_11-5820-520-34.pdf

And, from page 29:

*1-14. TRANSMIT SECTION CIRCUIT ANALYSIS. (CONT)*
A. Audio Amplification.
The audio intelligence is applied to either pin 17 or pin 16 of 
connector J1. Pin 17 is the input for
carbon microphones, and pin 16 is the input for dynamic microphones. 
Resistor A2R1 is used to
connect the required dc bias to the carbon microphones. Capacitor A2C1 
is used to block the
microphone bias from being applied to transmit audio attenuator A2Q1. 
Resistors A2R2 and A2R5
provide a voltage divider to reduce the higher input levels from the 
carbon microphones to one
near that of the dynamic microphones. Resistor A2R5 also provides the 
50-ohm termination for
the carbon

I'll bet they were anticipating the new family of audio accessories.

My two cents,
Al

Al Klase – N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/

On 9/3/2016 9:04 PM, B. Smith wrote:
> So it looks like using  using break out boxes for the connectors and 
> feed audio out from the GRA-39 C-2229 to pin "J" will drive the 
> GRC-106 mic input. Kinda like to figure this out now and not at 
> midnight at Gilbert after the pop corn Walt ?
> That will be the basic plan but wondering if we will have enough 
> drive? -- perhaps have a small amp for the mic line on standby?
> Z
>
> On 9/2/2016 6:16 PM, Tom B wrote:
>>
>> I should have added that pin J is NC on the H-33.
>>
>> Tom
>>
>>
>> On 9/2/2016 6:11 PM, Tom B wrote:
>>>
>>> According to the GRC-106 manual, the dynamic mic input goes directly 
>>> from 1A5 to pin J on both audio connectors J18 and J19.  It looks to 
>>> me like you could easily make it work with the GRA-39 with the 
>>> correct cable.  It looks like only one wire is moved.
>>>
>>> I have some cables here that have two U-228 connectors and one U-77 
>>> but I don't know what they were made for.  It would fit the GRC-106 
>>> for this application but I am not sure what these were for.
>>>
>>> I have seen a similar cable for the PSG-2.
>>>
>>> Tom
>>>
>>>
>>>
>>> On 9/2/2016 5:59 PM, WA5CAB--- via MRCA wrote:
>>>> It is still listed in SB 11-6 (FSC 6135 Primary Battery Supply 
>>>> Data) dated 28 May 1982.  I don't have anything more recent.
>>>>
>>>> But TM 11-5820-489-nn do not all date from 1983 through 1987.  The 
>>>> initial manual of the series, TM 11-5820-489-35P (which replaced 
>>>> SIG 7 & 8 AN/GRA-6) was dated 11 June, 1962.  TM 11-5038, which 
>>>> originally dates from 18 April, 1951, wasn't replaced by a 
>>>> long-number version until some time after Change 7 dated 16 May 1967.
>>>>
>>>> Robert Downs - Houston
>>>> wa5cab dot com (Web Store)
>>>> MVPA 9480
>>>>
>>>> In a message dated 09/02/2016 16:01:41 PM Central Daylight Time, 
>>>> RAFANTINI at salisbury.edu writes:
>>>>> The TM 11-5820-489 family of books all date from 1983 to 87 so the 
>>>>> AN/GRA -6 family of products were still in production and use 
>>>>> around the same time as the AN/GRA-39. I would speculate that the 
>>>>> GRA-6 was kept around just for that fact that it would directly 
>>>>> support the AN/GRC-106 family of radios. The GRA-39 always 
>>>>> appeared to be a newer and better box but maybe the more primitive 
>>>>> GRA-6 had its place?
>>>>>
>>>>> Will have to look and see if I can find production dates on my set.
>>>>>
>>>>> How long was the BA-414 (45 volt B Battery) available???
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> Ray F/KA3EKH
>>>>>
>>>>>
>>>>
>>>
>>>
>>>
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>>
>>
>>
>>
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