Quayhog

Odd amp to restore
« on: September 01, 2018, 07:38:39 PM »
I acquired an ARINC AFM-101 monitor amp.   It has some curious features and some impressive parts.  As near as I can tell it’s a monitor amp used by FAA facilities.  I think it’s designed to take BALANCED HiZ mic signal and route the signal through either or both 600 Ω or 8 Ω outputs.

The mic jack shares the same type jack as Electro Voice 666 mics.  The signal gets routed through a UTC H20 15k:80k interstage transformer, Then to a 6AU6 input tube.  The rest of the tubes are 12AU7 (PI) and push/pull 6AQ5.  Tube rectifier and 6E5 eye tube complete the tube count.

The output transformer is a UTC LS52 and has dual outputs.  The freq response is 7hz-50khz.  Way overkill for its intended purpose. L-Pad attenuators on the outputs.  The dataplate has a march 1960 date on it.

Now the question,  why would HiZ signal be transformer balanced and why did ARINC use such expensive parts?   After I get it working what would you modify it to do?


mjrippe

Re: Odd amp to restore
« Reply #1 on: September 02, 2018, 01:02:44 PM »
Can't think of a balanced HiZ microphone off the top of my head.  Perhaps it is a bridging input for line level signals?  Odd that they used the cannon xl connector though.

abbey road d enfer

Re: Odd amp to restore
« Reply #2 on: September 10, 2018, 12:28:13 AM »
I acquired an ARINC AFM-101 monitor amp.   It has some curious features and some impressive parts.  As near as I can tell it’s a monitor amp used by FAA facilities.  I think it’s designed to take BALANCED HiZ mic signal and route the signal through either or both 600 Ω or 8 Ω outputs.
The name suggests it was designed to receive line-level signals and drive either a loudspeaker or a tie-line.


Quote
Now the question,  why would HiZ signal be transformer balanced
The high input impedance means it could be used for eavesdropping on a 600-ohm line that's already loaded. At the time, broadcast systems were 600-ohm matching; you cannot put two 600-ohm loads on a 600-ohm output.

Quote
and why did ARINC use such expensive parts?
At the time, broadcasters were very rich and typically used what was best. 

Quote
After I get it working what would you modify it to do?
I wouldn't mod it, and use it as it was designed, anywhere a medium power amp is needed.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


 

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