[R-390] Servicing Advice on Signal Generator URM-25D

[Dallas Lankford]

The tube pin resistances seldom correspond to the values of resistors in an
R-390A (or other receiver).  And some of numbers in the tube resistance
charts are not even correct.  I have yet to see a resistor in an R-390A,
other than one that was burned brown or black (due to a short or whatever),
that needed replacing.  Like I said, if you want to know the value of a
resistor in an R-390A, you will usually have to "lift" one end, and then you
might as well go ahead and replace it.  But then we are back to the
"resistor replacing" game, aren't we?   (though perhaps not what the
original rersistor replacers intended)

Black beauties?  Where are the "black beauties" in an R-390A?  I have seen
lots of R-390A's, from the first production Collins's and Motorola's to the
1967-68 EAC's, and I have never seen a black capacitor in an R-390A.  Surely
you are confused, and thinking of the SP-600.

Have fun,

Dallas


----- Original Message -----
From: <DCrespy at aol.com>
To: <r-390 at mailman.qth.net>
Sent: Monday, January 10, 2005 8:45 PM
Subject: Re: [R-390] Servicing Advice on Signal Generator URM-25D


>
> Dallas' note below.. He makes a great point, if it isn't broken, don't
.....
>
> About resistors, just check the resistances from the tube pins to  ground
> (most manuals have a chart).  I usually find at least one with  a problem
to
> correct. Otherwise, no wholesale replacements.  (I  confine recapping to
> electrolytics and black beauties.)
>
> 73
> Harry   KG5LO
> Saline MI  :
>
> Sure.  Let me prerface my remarks by saying that much of what is  said
about
> preventive maintenance on the reflector is baloney.
>
> Take, for example, the "resistor replacers."  You can't measure  most
> resistors accurately in circuit unless you "lift at least one end," and
if you do
> that, you might as well go ahead and replace  it.
>
>
>
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