[R-390] A vs non A

[Charles P. Steinmetz]

Ed wrote:

>I also just finished looking through the R-390 manual to see what it 
>said about alignment and confirmed there is no reference to 
>sweeping.  To be fair, the description of transformer coupling to 
>achieve the passband is correct, but unless there is a means to 
>adjust the coupling then the best you can do is to align all at the 
>center frequency, and sweeping won't make it any better.
>
>      *     *     *
>
>>The Alignment procedures are in TM 11-5820-357-35, 9 March 1962.
>>This begins on page 91.

Peaking works to get the undercoupled stages on center frequency, but 
not the overcoupled stages.  If you peak an overcoupled stage, you 
will end up with one of its two peaks at the IF center frequency and 
an asymmetrical overall response.  If I had to do this in an 
emergency without sweep facilities, I'd try peaking the overcoupled 
stages on a good strong broadband noise source like a noise diode 
rather than at a single frequency, and I'd do those stages last, 
after peaking the undercoupled stages.  It's been a long time since I 
fiddled with a 390 IF, but ISTR there is one overcoupled stage.

Regarding the alignment procedures given in the 390 TMs, as I said in 
my 10/9 post:

>Note that the IF alignment
>procedures given in the TM-11-5820-357-35 (1962) and TM-11-856 (1955)
>manuals do NOT stagger-tune the IFs -- if you read carefully, they
>both state "Perform the procedure outlined . . . below only when the
>transformer cores have been displaced greatly from their normal
>positions within the cores."  In other words, "This procedure will
>get you back on the air, but will not return the radio to its proper
>IF alignment."

This is at TM-11-5820-357-35 p. 93 paragraph e(2) and TM-11-856 p. 
118 paragraph d(2).

So yes, there is a procedure given in the TMs to align 390 IFs.  But 
the authors were clear that it was not a routine procedure.  Rather, 
it was to be used "only when the transformer cores have been 
displaced greatly from their normal positions within the cores" due 
to damage or previous gross misalignment.  The reason, which the 
authors clearly knew but did not see the need to explain, is that the 
procedure given will not return the IF to its factory alignment 
condition but could restore basic functionality.

Best regards,

Charles