[R-390] More R-390A Questions...

[Mike Melland]

I've been ringing my "new to me" R-390A out all weekend. 
 I received it last Wednesday.... It's a Motorola, serial 
number 714 from the 1956 contract.... parts inside have 
1955/56 date stamps on them.  I noticed that the PTO is a 
Collins.  I have checked over most of the things all of 
you told me to check and find that the radio works very 
well indeed.  It is very clean inside and the front is 
also in nice shape.... has all internal covers plus top 
and bottom as well as tube shields (silver ones) and has 
what appear to be the original meters.  It does not appear 
to have any modifications at all.  Everything appears to 
work pretty much as it should.

I do have a couple of questions that perhaps some of you 
could answer for me.

How linear is a Collins PTO ?  If I calibrate against the 
calibrator at for example 6.000 MHz and then turn up to 
6.900 MHz and re-check against the calibrator It's off 
about 1.0 to 1.2 kHz high.  

If I listen to my local AM station at 1.490 MHz and have 
the radio set up medium AGC, RF gain up all the way at 10 
I read about 80 dB of carrier level and the audio sounds 
fine.  However if I leave the radio on for several hours 
and return I notice the audio is distorted.  If I then 
reduce RF gain a bit I hit a point where the audio clears 
up and is fine.  I can then turn up the gain again after a 
bit and the audio remains fine.... but will eventually 
distort again.  This seems to happen only on this very 
strong very local signal and in the 4,8 and 16 kHz filter 
positions.  MGC appears to work normally. Is this overload 
when in AGC ?  Is it normal ?  What would be likely to fix 
this if it's a problem ?

BTW.... I was checking Chuck's procedure for adjusting IF 
gain.  What is meant by "terminate antenna" ?  If I put it 
into a 50 ohm Bird load I hear nor see any receiver 
noise.... perhaps it means tune to 15.2 MHz with the 
antenna hooked up to hear background noise ?  At any rate, 
the carrier needle on mine using the antenna hooked to a 
dead spot around 15.2 pins to the right when using the 
procedure to check the IF gain.... could that be part of 
the cause of the distortion when listening to a very 
strong signal in AGC if the gain is in fact set too high ?


Thanks,

Mike, W9WIS


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Michael Melland, W9WIS
Winneconne, WI USA