[R-390] R-390 Mechanical Alignment

[Jacques Fortin]

Hi Tom,

 

I've been thru this recently...

 

1_ The Collins manual for the R-390, dated 23 October 1953 is OK: the position of the cams HAVE TO BE looking like in the "figure 44" when the tuning is at 2.000.

The corresponding figure is 91 in the 1953 manual.

 

2_ The Army manual TM11-856 is COMPLETELY WRONG when it states the position of the of the second IF cam in the Chapter 110 1) (P.116):

"The position of the second if cam shown in figure 90 represents the correct position for high end of the band (the last three digits of the frequency indicator should read 999)". The figure # is 90 there.

I do not know who was responsible, but the preceding text between quotes makes absolutely no sense (As you doubted of...) and should be disregarded.

 

3_ Surprisingly enough, this nonsense was perpetuated in the TM11-5820-357-35 of 9 March 1962 Chapter 73 1) (p. 88) (same text....).

 

I admit to have scratched my head for a few hours when I began the alignment of my Collins sn 2074.

But I finally figured out that this paragraph made no sense and aligned the cams at the 2.000 position, then all the rest of the alignment went on beautifully.

So the proof is in the pudding, should I say.

My set is now running as new, but with some modifications:

_ 12BW4 rectifiers

_ 6080 regulator tubes

_ W7DI "improved" product detector with Larry Haney’s AGC modifications.

_ Modified squelch circuit (original one being incompatible with the W7DI product detector scheme).

 

Good luck with your own R-390 !

 

73, Jacques, VE2JFE in Montreal

 

 

Working my first R-390 (Been through a few 390A's) and I have a question about the cam alignment statement in the manual (different sections and fig numbers depending on version you are looking at).

I'm looking at the TM 357-35, 1962 version and in section 73 a.1 it states that the image in figure 44 shows the cam position of the 1-2mc cam bisecting the alignment line and states this is for the "low" end of the band. I can agree with this as the slugs are fully engaged in the RF modules for low end adjustment.

It then goes on to say that the second IF cam shown in that image is shown at the high end of the band (indicator reading 999). When I tune to the high end of the band, my second IF cam is not in this position. It is almost in the opposite position where the slugs are fully engaged in the RF modules. I would expect the slugs to be out of the modules at the high end of the band so the trimmers could be adjusted. Is the text wrong and the image of the cam position for the second IF is really at the low end of the band - not the high?

There is another section in the manual where it references the same image and says that it shows the cam positions at 0200 - which all my cams seem very close to aligning with.

TomW3TA