[Milsurplus] Re: [ARC5] Re: RU/GF documentation

[Mike Morrow]

>I haven't carefully check the earliest models but would be surprised if they 
>aren't the same way.  All of the (later anyway) GF transmitters and RU 
>receivers are wired for 14 volt heaters. 

Wasn't the first 24 vdc version of the RU-series the RU-12?  I know that the RU-8/GF-6 (02/1938) and RU-9/GF-7 (10/1938) were both 12 vdc, but I lack any further documentation until the RU-16/GF-11 (04/1941) sets. 

With respect to the location of the receiver bias resistor, the earliest manual I have (GF-1/RU-3, 02/1934) shows its location in the dynamotor unit, so that's where it appears to be on all the RU/GF receivers, as opposed to being in the receiver itself like it is for the stand-alone one- or two-receiver systems like the RU-18/19.

>A quick ID method for an RU receiver that doesn't have a nameplate is to look 
>at pin 77 in the connector.  The RU's that came with GF's have a wire going 
>to the cathode of the 77 AGC tube.

Yes, that's the connection to the tap on the bias resistor that's located in the dynamotor unit.

Weren't the RU-11 and RU-12 designed as stand-alone receivers similar to the later RU-18/19?  If so, I would guess that the bias resistor location would be these same...in the receiver unit.  That would also be consistent with the RU-19 manual saying that the RU-19 receiver system is interchangable with the RU-12.

I'm sure that the reason for having the bias resistor located in the receiver instead of the dynamotor unit stems from the fact that *two* receivers may be operated *simultaneously* from the common dynamotor unit in the stand-alone RU system.  If a common bias resistor were used in the dynamotor negative power lead in the dynamotor unit, as it is in the one-receiver-only RU/GF models, then the current draw of two receivers through it would greatly affect the bias voltage generated.  By putting the bias resistor in the receiver, the bias resistors of the two receivers are in parallel in the negative current path of the dynamotor.  That maintains the bias generated across the resistors the same no matter if one or two receivers were being powered from the dynamotor.

Mike / KK5F