[R-390] R390A Audio Meter FS

[David Wise]

TB102 serves multiple purposes.
CR101, between terminals 3 and 5,
is for Diversity AGC.
Terminals 1 and 2 let you open-circuit the
RF GAIN control.)  Terminals 6-8 are LOCAL AUDIO.

The LINE AUDIO output is actually on TB103,
terminals 10-13.  If you go to TM11-856A
Figure 5-13, Schematic Sheet 4 of 4,
in regions 1A to 4C, you will see that M101
has no polarity and (with an attenuator pad)
is across the secondary of LINE AUDIO transformer
T602 with no diode in sight.

Dave Wise

>-----Original Message-----
>From: rbethman [mailto:rbethman at comcast.net] 
>Sent: Tuesday, September 21, 2010 12:21 PM
>To: r-390 at mailman.qth.net
>Cc: David Wise
>Subject: Re: [R-390] R390A Audio Meter FS
>
>  I suggest you go look at TB-102.
>
>Note the CR-xxx that is mounted there.
>
>I wasn't aware that anyone needed to "prove" what is in the circuit or 
>the manual.
>
>I simply restore these for MY purposes.  One '67 EAC and a Collins '51 
>contract from St. J's.
>
>Members of the list have a tendency to focus in on "small" areas, NOT 
>open their minds and eyes to the WHOLE!
>
>Bob - N0DGN
>
>On 9/21/2010 3:00 PM, David Wise wrote:
>> Not yet.  The only place it's marked with a polarity is on the
>> Mainframe Wiring pictorial diagram, and that's nonsense,
>> because M101 is fed with audio AC.  That puts at least a
>> rectifier inside, so although you can determine the FS
>> current externally, to measure the resistance you have
>> to bust it open.  It could be a 17-ohm movement, but
>> you haven't proven it.  I hope it is...
>>
>> Dave Wise
>> SWL in Hillsboro Oregon
>>
>>> -----Original Message-----
>>> From: r-390-bounces at mailman.qth.net
>>> [mailto:r-390-bounces at mailman.qth.net] On Behalf Of rbethman
>>> Sent: Tuesday, September 21, 2010 11:15 AM
>>> To: r-390 at mailman.qth.net
>>> Subject: Re: [R-390] R390A Audio Meter FS
>>>
>>>   Please pull out the TM 11-856A.
>>>
>>> As you go through the schematics, you'll note the BOTH 
>meters have a +
>>> and a - connection.
>>>
>>> Keep digging and reading.....
>>>
>>> These are the SAME interior devices with different faces.
>>>
>>> Bob - N0DGN
>
>