[R-390] R-390 progress!!

[frank hughes]

Hi,
This is a progress report, bringing a "basket case" R-390 back from the
dead.
Found this one at the Orlando Hamfest in February 2013.
Unit looked complete, even had the covers.

I was looking for a replacement for the R-390A I use for AM nets, I just
like the sound of the R-390 better.
Also, the filters in my "A" are starting to go off, not looking forward to
the mechanical filter challenges.

I was tempted to replace the R-390A IF deck with an R-390 IF deck, having
just read an excellent article in an old ER on how to do it.
However, it looked like less work and more fun to find an R-390 and try to
get it going.

The Hamfest R390 did not work,( B+ was over 300vdc) and the IF deck had a
foot long piece of mystery coax soldered to pins under the deck.

With the super help and advice of folks here, the B+ regulation was
restored to 180vdc.

R626 had drifted WAY up, replaced it to restore regulation.

3/8A fuse kept blowing, turned out that there was a shorted 26Z5W.

Some resistors in the power supply were smoking, in spite of the "no
smoking" sign clearly posted on the wall for all to see!

Replaced the resistors R801-R804 with the suggested wirewounds.

Replaced the power supply CR801 w/ a modern full-wave bridge rectifier.

Replaced 3TF7, V801, V802 26Z5W's w/ Kurt's excellent solid state units.
Replaced V605,606 6082's and V608,609 with Tom's wonderful solid state kit.

Although it is now a little disappointing that I can no longer use the
6082's as a source for heat-shrinking Teflon tubing,
I will learn to live with it.

Super-glued the broken slug I found in the RF deck.
It was broken off at the top, where the spring is inserted, so I will have
to wait until I get to the RF alignment to see if it works.

Went to my pile'o hoarded R-390 IF decks and picked a clean looking one to
install.

Some weak tubes prevented  -7vdc appearing @ Diode Load, but fresh tubes in
V501-V506 brought the signal level up
to where it should be for starting alignment.

Friday I downloaded the 1955 TM 11-856 from
http://www.jamminpower.com/main/r390.html, started working on
"111 Alignment of 455-kc If Stages".

Injected 455kc into test point E210.

Was amazed to see how much signals came up by peaking T506-T501 and T207!

Stopped at "j" in section 111.
Adjusting the phasing capacitor in crystal filter Z501 is very weird, ie;

"Continue tuning the generator in this direction until the voltage output
required to obtain the original
reading on the vtvm is 1,000 times the voltage required at peak frequency"

I am going to read more before I try it.

Anyway, I am very encouraged and believe it there will soon be another
R-390 in use on the AM nets!

Thanks very much for all the help to get it this far!!!
73
Frank
KJ4OLL