[ARC5] R-27/ARC-5 Hookup Question

[J. Forster]

I am still puzzled as to why they'd go to the trouble of bringing out the
terminal. Some assembly line ladies spent years putting in that wire,
after all!

If it was useful to serve as a sort of BITE it makes sense- a sort of
quick final test at the depot or radio maintenance shop- to decide whether
the radio was OK to go in a plane or needed service.

I don't really buy it was put in solely to test the 2x 7000 Ohm divider
resistors.

Can anyone think of another radio that has such a provision?

YMMV,

-John

==================



> Well, to a degree.  Remember that this is a *composite* voltage reading
> of the 1st and 2nd IF amp screens, and indirectly through a 200 ohm
> isolation resistor, the RF amp and mixer screens (using the AN/ARC-5
> example.)  So if all four tubes had low emission, it would in fact
> decrease the average screen (and plate) current, so the screen voltage
> indication would edge toward the higher end of the range.  That won't
> pinpoint a specific tube, however.  If one of the tubes had a gassy
> condition, it would bring the screen voltage down (perhaps not enough to
> take it below the low limit, however)...but then the radio would
> probably not be working very well. :-)
>
>   - Mike
>
> On 7/20/2013 9:12 AM, J. Forster wrote:
>> OK.
>>
>> Next question, does the screen current of tubes give an indication the
>> tubes are getting 'weak'- having low emission?
>>
>> I can see that it would change w/ gas.
>>
>> -John
>>
>> ==================
>>
>>
>>
>>> It's basically a go/no go indication, John.  There is a range of normal
>>> readings, and if it's outside that range, then you have to use your
>>> noggin and the Theory of Operation and Maintenance sections of the
>>> manual to find out why. (cf. Paragraph 5-18 in the AN/ARC-5 manual for
>>> the process.)
>>>
>>>    - Mike
>>>
>>> On 7/20/2013 8:18 AM, J. Forster wrote:
>>>> Mike,
>>>>
>>>> Do any of the manuals on the receivers or test sets give any details
>>>> about
>>>> the use of screen voltage in testing or aligning the receivers, or is
>>>> it
>>>> just a go/no go indicator AFAYK?
>>>>
>>>> -John
>>>>
>>>> ============
>>>>
>>>>
>>>>
>>>>> On 7/19/2013 7:51 PM, Kenneth G. Gordon wrote:
>>>>>> On 19 Jul 2013 at 14:46, J. Forster wrote:
>>>>>>> Does anyone have an opinion why they bothered to bring the screen
>>>>>>> saupply
>>>>>>> out to a pin?
>>>>>> In my opinion, it was used when testing the receiver to make sure
>>>>>> those
>>>>>> two black wire-
>>>>>> wound resistors in the rear were OK.
>>>>> Exactly right.  See the Command Set Test Equipment page at
>>>>> http://aafradio.org/docs/Command_Set_Test.html and the SCR-274N test
>>>>> set
>>>>> page at http://aafradio.org/docs/ARC_Test_sets.html
>>>>>
>>>>>         73,
>>>>>     - Mike
>>>>>
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