[R-390] R-391 restoration update

[Paul H. Anderson]

Howdy folks,

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

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

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

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.

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.

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).

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.  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.

Paul