[R-390] R-391 restoration update

[Paul H. Anderson]

On Wed, 27 Feb 2002, Barry Hauser wrote:

> Paul wrote:
> > Last I wrote, I think I was asking about motor bearings and brushes for my
> > R-391's autotune.
> 
> > Since then, I was able to buy standard bearings, cobble up some worthwhile
> > brushes, install the motor, figure out the autotune, get it aligned and
> > working, and move on the the electrical part of the radio.
> 
> Were those the bearings for the motor or the worm drive?  Hope you took down
> names 'n numbers, part numbers, that is... ;-)

The motor bearings.  I haven't yet tackled the oillite bearings in the
aluminum frame for the line shaft.  Doing this requires more bench space
than I had at the time.

> I don't know if they ever came out with anything after the preliminary. The
> '391 should be electronically the same as the non-A.  Only electrical
> difference would be in the wiring harness, but I think you mentioned that
> this appears to be an add-on to support the autotune electricals.  So, it's
> probably safer to use a non-A manual for the electronics, although the '391
> book warns that some units may vary (ancient YMMV message), but I thought
> they were referring to the autotune mechanics.

I think I will be able to write out a list of specific parts added or
changed for the R-391 (over the 390).  I think there are very few parts
that were changed (as opposed to added), although they were large
physically (front panel, autotune frame, and wiring harness overlay).

> Yup -- you're into boatanchor archeology and forensics now.  I find that
> kind of stuff all the time - tube  voltages and resistance specified for
> pins with no connection, crazy resistances vs. the schematic, and so on.  I
> get the sense that some of this resulted from arbitrary production line
> switcharoos -- like using a different unused tube socket terminal as a
> tie-point than originally assumed.  Of course, many of these were serviced
> and then re-MFP'ed.  However, if your radio agrees with the non-A manual,
> that's a 2/3rds majority vote. ;-)

Funny that you mention that - last night, I was also surprised to see that
the physical layout of the wiring of two R-390 AF decks were different.  
Collins had done a slightly more complex thing, and Motorola had
simplified it to make it easier to build, and required one fewer posts.

> That's why solid stating out the 6082's may be in the best interests of
> preserving these.  The deck is upside down so the heat from them rise into
> the module wiring.  If you run the 6082's, it's recommended to add a small
> muffin fan alongside the chassis lined up on the portholes, set to exhaust
> air out.  Or, you can run the rig upside down so the heat rises up and out.

Agreed - the 6082's get hot enough to discolor newspaper - I had the AF
deck out of the radio, but hooked up.  The tubes laying against newspaper
cooked it (over a 30 minute period or so).  I doubt they'd burst into
flame, but I wouldn't want to put anything flammable next to them just the
same.

> >
> > Knowing what I know (or think I know) now, I do believe I'd just replace
> > every cap and resistor in the AF deck before worrrying about trying to use
> > it.  Even resistors on the board near the 6082 tubes were fried to a
> > crisp.
> 
> Dave Medley recommends replacing all the 47 ohm resistors (2 watt, I think)
> with 5 watt "sandohm" types -- the squared off wirewounds.

Oh yeah - at the very least.  I think as preventative maintenance, the
other 1W and 2W carbon comp resistors should be replaced.  The 330K to the
hum control pot and a few 82K ohm ones come to mind.  One AF deck had at
least 8 BBQed resistors, the other one was better, but still pretty bad.

>   I don't think I'd apply this same strategy to the IF deck, but if
> > I start replacing capacitors there, I'm gonna do all the resistors, too -
> > they just drift too much from heat, like from the soldering iron.
> 
> Keep up the good work ...  Need that article AND some good guidance to do my
> own '391's.  While you're at it, would be a good idea to document the
> apparent errors in the manual - might be the beginning of a Y2.002K edition.

Since as you say, the 391 manual never made it to a next revision, maybe
it would be worth doing an R-390 manual with a chapter covering the
autotune specific parts of the 391 manual, so it would cover both radios.  
I can't really think of anything wrong with that, since the core
electrical circuits are identical.

Does anyone offhand know what documentation production system was used to
generate the Y2K R-390A manual?  Specifically, what text and graphic page
layout program?

Thanks,

Paul