[R-390] Resistors for the R-390A and beginner help

[Tom Warren]

So Bob (actually, I'm serious), how about telling us about PTOs and Collins'
troubles in getting them designed.  I've seen one or two things, but haven't
found the articles where the Collins boys talk about the drifting
permeability of the iron oxide (or is it ferrite?) cores and the shrinking
coil forms.  Where is this all discussed.

It'd be nice to hear a bit more discourse on why the radio can stand a wider
tolerance band than is specified.  Except for about 7-10 places (excluding
the very few resistors in parallel with an inductor)  in the entire radio,
you can measure all the resistors as if they were out of circuit.  Seems to
me that I actually lifted only one resistor in the IF deck to accurately
measure its resistance.  There are those 7-10 places where resistors are in
parallel with the one you want to measure, and generally it's simple to do
the parallel equivalent and measure that number.  It's slightly more
complex, but not much.  The only resistor in the entire radio I really quake
at replacing is a two-watter buried under the mech filter switch and up
against one of the shields.  Fortunately, that one wasn't bad in both my
radios.  Also in tight places, you can leave part of the old component lead
then use a bit of 1/16" copper (copper, not brass, as copper is easier to
solder) tubing (available from many hobby stores) as a sleeve to fit over
the end of the new component and the old lead.  Crimp on the end of the new
component and solder in.  Doesn't look too bad and serves the purpose.
Others will suggest wicking the old solder from the original joint of the
old component and resoldering that in addition.  If more detail is needed,
write me, and I'll find some old e-mail correspondence.

Thanks,
Tom, W4PG

PS:  I'm currently working on a Progressitron and a Cosmos.  Among other
reasons, that's why I want to know.

----- Original Message -----
From: "Bob Camp" <ham@cq.nu>
To: "Jim Miller" <jamesmiller20@worldnet.att.net>;