[ARC5] SM-30 URM-14

[WA5CAB at cs.com]

The transformer output impedance isn't given but I would guess on the order 
of 50 ohms at 1 KC.  

The purpose of the 82 ohm resistor is to limit the current from the 
transmitter's carbon mic bias current supply.  It is in series with the transformer 
secondary to ground/case.

The Output jack takes a PL-68 or PJ-068.  The sleeve is connected to case 
and to the bottom of the transformer which is also connected to case.  The 
so-called mic current jack (takes a PL-55 or PJ-055B or R) is insulated from 
the case so that if an external MA meter is jacked into it, the meter reads 
the current through the 82 ohm resistor and the transformer secondary.  If 
you made the mistake of plugging a double-ended cable into the mic current 
jack and into any jack on the transmitter, you would short out the mic bias 
supply.

In a message dated 03/21/2017 14:56:17 PM Central Daylight Time, 
releazer at earthlink.net writes: 
> "Does anyone know the output impedance of the matching transformer. What 
> is the purpose of the series 82 ohm resistor in the output?"
>  
> That Mic Current jack is one of the type that opens up to accept a plug 
> and if no plug is installed the circuit is just straight through the Mic 
> Current socket from the Output socket to the 82 Ohm Resistor.  The Mic Current 
> jack is supposed to accept an external meter.  It shows one side going to 
> the outer shield but on that socket it appears to insulated from ground. 
>   
>  The schematic says that the single tapped side of the transformer is "1.2 
> Ohms DC Resistance"  The winding on the other side of that transformer is 
> marked 500 - 1000 - 5000 
>  
>  Wayne 
> WB5WSV  . 
> 
> 

Robert & Susan Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480
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