[R-390] R390A Basics Finished

Fri, 9 Apr 2004 11:16:39 -0400

Hi All,

Well folks, I have finally completed the basics on my 1960 Stewart Warner.
This radio had good synchronization and basically worked on all bands like a
normal radio. All tubes were tested as good. I had five problems which were
driving me nuts:

1. The classic stuck ON power microswitch
2. I had a weak band (8-16 MHz) with no antenna trimmer action
3. Sensitivity to varying wildly day to day. Shorting the hot plate trimmer
on the RF coils to ground (Z20x series) would temporarily fix the problem -
spark!.
4. Cal signals weak.
5. I had a a weird audio gain control problem at the top of the range and
generally low audio gain.

Anyway, I did the did the basic IF Module and Audio Module cap and resistor
changeouts and pulled the front panel and did the RF Deck. The power supply
was inspected but not touched. 149.9 Volts on E-607. I also did the typical
gearset cleaning using Mystery Oill and a lube with Mobil-One. The thing was
reassembled. I then did a quick tune up per the manual.

The results:

Main AC Microswitch - The stuck microswitch was indeed stuck but after
removing it and inspecting it, the contacts were not fused; the u-shaped
flopper was not flopping. A slight bend to the spring metal that pushes it
fixed the problem. I cleaned the contacts and re-assembled it, testing for
contact action as I performed each step. By the way, this switch can be
installed backwards and it actually still functions. The power wires will be
on the wrong side of the switch!

Weak Band - After re-furbing the RF Deck and reinstalling everything, the
Front End coil assembly was removed from the top of the deck and
dis-assembled. I simply hit the trimmer with deoxit and cleaned the
contacts. The band came back and the front panel trimmer now worked on that
band.

Intermittent Sensitivity - The paper caps changed in the RF deck apparently
fixed this. Just as a precaution, I changed several of the 0.005 1KV caps
around the RF amplifier too. No idea which one fixed it. Found a weird thing
at C257. It was a 47 pF NPO dogbone cap but no C227 at all. I added C227,
0.047 uF in parrallel with it.

CAL Marker - Besides replacing the paper caps and a couple of 1/2W
resistors, I found that the resistors in the plate circuit of the
multivibrator, R224 and R226 were pretty much cooked and double value so I
replaced them with 10K, 1 Watt flameproofs.

Scratchy Audio - The audio module got the treatment and I found that the
front panel audio pot had a value of 5K instead of 2.5K. I must have put
this in years ago not realizing that the cathode followers could not
tolerate the DC bias shift. I found the original pot and disassembled it,
cleaned it and replaced it. This was all it took.

After a quick tune up, the radio is a new beast indeed. All on my list
responded beautifully. I used the NTE MLR-Series dark orange mylar film caps
throughout. These caps are just as inexpensive, available and fit better
than the Spragues. Here is the data sheet on the NTE caps:
http://www.nteinc.com/capacitor_web/pdf/mlr.pdf

Next - AGC, Product Detection and Audio improvements.

MM

----- Original Message -----
From: "Roy Morgan" <[email protected]>
To: "Jim Brannigan" <[email protected]>; <[email protected]>
Sent: Wednesday, April 07, 2004 10:29 AM
Subject: Re: [R-390] CV-591 Audio

> At 07:55 AM 4/7/2004 -0400, you wrote:
> >I just completed a substantial re-build and alignment of my CV-591 SSB
> >converter.
> >
> >The audio output is still low.  The Audio gain must be fully open to to
get
> >any reasonable audio output.
>
>
> There are various arrangements of the audio output and rear panel jumpers.
> Study the manual to see if you have the thing set up right.  If I remember
> right, one output arrangement delivers 10 milliwatts or some low power,
and
> the more normal arrangement delivers rated output.  The normal output is
> not very high. I suggest you run the line output to a small external
amplifier.
>
> Roy
>
>
>
> >Is this a drive problem from the R-390A?
> >Has anyone else experienced this problem?
> >
> >Thanks,
> >Jim
> >
> >_______________________________________________
> >R-390 mailing list
> >[email protected]
> >http://mailman.qth.net/mailman/listinfo/r-390
>
> - Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
> 7130 Panorama Drive, Derwood MD 20855
> Home: 301-330-8828 Work: Voice: 301-975-3254,  Fax: 301-948-6213
> [email protected] --
>
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