[R-390] R-391 restoration update

[Barry Hauser]

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 mechanical autotune is quite a piece of work - simply amazing the
engineering that
> went into it.

And a good deal of combination-locksmithery.  I think one of the consulting
engineers was R. Goldberg.

>
> I did take a lot of notes, and with any luck will be able to write an
> article about it for Hollow State News.

I have you penned in - with ink, actually carved in .... heh heh.

> The manual is an interesting combination of amazingly simple, plain
> language, and also a lot of wrong information.

That wrong information stuff is what triggered the development of the Y2K
manual.

>
> This evening, while studying the 1ST IF Amplifier circuit diagram, I
> finally realized that the 391 manual (preliminary one) has bad circuit
> diagrams!  The schematic circuit around the V501 tube is all wrong.
> Fortunately, the R-390 manual has the right diagrams, so tracking my IF
> deck problems should be easier now.

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.

As you discovered earlier, the manual also has the worm drive access for
autotune resynch on the wrong side of the rado -- unless they meant from the
radio's point of view.

>
> Are there other known problems with the schematics?  I've also come across
> resistance values in the voltage/resistance charts that just can't be
> possible, given the circuit diagram.  Boy, that keeps me on my toes.

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. ;-)

>
> Oh - this weekend and last night, I was able to trace the RF signal all
> the way through the radio - I spent the longest time in the AF deck,
> replacing and repairing all the heat related damage there.  I'm still not
> done - I think at least two or three of the .01 uF caps are leaking (grid
> caps for the local and line amplifier tubes).

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.

>
> 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.

  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.

Barry