[R-390] R389 and R390 faults

[Roy Morgan]

At 12:42 PM 3/21/2006, you wrote:
>Hi.
>      I have recently bought an R389 and a pair of R390 rxs. They are all 
> complete and in good condition.
>At first appearance it seems as the PSU, Audio stage and IF strip are 
>interchangable.

Yes, they are. In the R-389, the widest (two(?)) IF bandwidths are not 
used.  This is because of the inherent narrow bandwidth of the R-389 RF 
tuned circuits.

>1.Were any parts listings produced for the above rxs, ie detailing the 
>wattage of resistors and the voltage ratings of other components?

Yes.  Find and study the manuals for both radios.

>2.Are there any common faults or other troublesome components that fail or 
>give trouble that I need to be aware of?

Yes.

1)You really need a fan on the voltage regulator sections. See:
http://home.comcast.net/~roysmorgan/
click "fanplate"

2) the 47-ohm, 2-watt resistors in the voltage regulator section (audio 
deck) and in the power supply rectifier section should be checked. You will 
likely find them all drifted upwards in value at least somewhat. All should 
be replaced with modern, higher wattage resistors.

3) In the R-389, the MAIN TUNING KNOB has a clutch built into it. If it is 
frozen or corroded, it can lead to RUINOUS damage to the PTO if you force 
the thing by hand, or hold it while running the motorized tuning. The R-389 
PTO is nearly unobtainable. I know of one and one only that has been sold 
in the last 10 years.

4) In the R-389 you are in danger of ruining the motors if you run them 
without new lubrication. One motor moves the main tuning dial and is 
controlled by a switch on the front panel, and one motor automatically 
changes RF tuning sections as the tuning is moved through it's range.

>3. I have a couple of R390A rxs which have a mechanical counter for the 
>BFO, why was this used over the standard knob?

It replaced the standard knob.  It was used by intelligence gatherers doing 
radio intercept to both accurately set sideband and CW BFO offsets and to 
measure signal characteristics. They were, in fact, common ten turn counter 
dials which embodied both counting and mechanical reduction of 
motion.  There is nothing secret or especially rare about the turns 
counters. What they were doing with them is possibly still classified.


Roy


- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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