[R-390] Starting R-390 restoration - My $.02

[chuck.rippel at cox.net]

Not being a nit-pick on Mike but will expand on his points just a bit.  

---- k2cby <k2cby at optonline.net> wrote: 
> I am sure most of you will regard this is heresy, but here’s my two cents
> worth.
> 
> First of all, by all means DO REPLACE the “killer capacitor” C-553 .01 µF
> 300 dcwv in the IF deck immediately preceding the mechanical filters. That
> should be first on your list. 

Well agreed .  Failure of C553 destroys the mechanical filter selected by the front panel switch. .01 Orange Drops are largely rated at 600VDC, suggest one of those.   There is little value in going overboard (I've seen 2KV caps used to replace C553) but the additional voltage headroom cannot hurt.
 
> I have, however, added inrush current protection in the form of a CL-80 varistor, and the receiver is plugged into a surge-protected outlet.

We differ here.  I'm coming to the conclusion that the highest failure cause in the receiver is shaping out to be open power transformers and I'm about convinced its caused by inrush.  There is a better, safer approach than using the varistor "fix" IMHO.  I'm working on the prototype of a more realistic fix and will, with the owners permission, install it in the R390A I'm currently working on.   

The design is close to being done and I'll be sharing it openly.

I pull those varistors in receivers I restore.  My concern is how hot they run along with the that particular installation being a misapplication of the component.  That said, I'd rather have my varistor burn in half the the primary of the power transformer.

 
> Second, there’s nothing whatever wrong with “Orange Drops.” They are fine,
> high-quality capacitors, and I used them when I recapped my own R-390A.
> Let’s face it, however, Orange Drops were not designed for RF service (nor,
> for that matter, were the “Brown Beauties.”). For my money, it makes a lot
> more sense to replace the “Brown Beauties” with ceramic capacitors in all of
> the RF applications. The “Brown Beauties” were axial and tubular. Orange
> Drops are radial and stand out like sore thumbs, so matching the original
> appearance isn’t an issue. Ceramics take up a heck of a lot less space, have
> far better performance characteristics at RF, and are outstandingly
> reliable. They were my first choice which I re-capped my SP-600.

I rely on polystyrene media Orangedrops in any circuit which passes signals up to the 455kc IF.   They work very well and
replacing them in the audio chain actually makes the audio sound smoother.  Because of clearance, 400 or 600V tubulars go in the AF deck.  One can squeeze in Orangedrops at the risk of breaking solder pads and compressing the board on the bottom of the audio deck.

Ceramic discs for anything which handles RF over 455 kc.

DON'T REPLACE EVERY CAP IN THE RADIO !!!  This is especially true in the RF deck.  You wanna really screw up an R390A?  Fiddle around in the RF deck.

On the final subject of capacitors, rebuild, replace and locate under the chassis or buy the replacement on E-Bay, the 2 filter caps !!!!!    Any originals are leaking electrically right now.  They will also leak acid out of the bottom of the cap.  I like the radios to look original and prefer to rebuild the caps in the radios I work on.  Nothing wrong with locating them under the chassis leaving the originals showing.  The caps off E-Bay work; I don't care for their looks and am unsure of their advertised quality.  "Unsure does not equal "bad,"  it means unsure.

> That said, I would still use Orange Drops in the audio stages, mainly
> because they are more economical than anything else in the higher values.
> One vital point:  C609        ELECTROLYTIC: 8 µF, 30 dcwv. wet tantalum
> capacitor is as bad for the Audio subchassis (it leaks corrosive gunk) as
> C-553 is for the IF subchassis. Replace it with a 10 µF, 35 dcwv
> electrolytic or a tantalum (if you want to travel in style).

Yep, yank that one.  Pay attention the polarity of the replacement.   As I recall, the positive lead of the cap faces inboard on the audio chassis.
 
> STAY AWAY from the corrector stack on the PTO unless you are prepared to
> make a career out of adjusting it. Been there. Done that. Gave up. Parted
> out the PTO.

A career and retirement.   Stay out of the PTO.

> I have rebuilt the R-390A gear train. Given a good manual like the “Y2K” is
> it not a forbidding experience if you take your time. On the other hand, I
> wouldn’t do it unless there is a good reason to.


Stay out of the gear train.  Getting the timing and cam placement as it relates to the electronic operation of the radio are critical.  The Russians stole an R390A during the cold war in an attempt to duplicate the technology in the Workers Paradise.  They gave up. 
 
> Other than re-capping, take time to be sure that the switches – especially
> the bandswitch – are clean and sparingly lubed.

Well agreed on the bandswitch stacks and will add the selectivity switch.  I use a small flux brush which have had the bristles shortened to about 1/4".  The object is to try and scrub the black corrosion off the rotating CONTACT FACES.  Don't even try to clean the small contactors.  You'll spread gaps and the switch will be done.
> 
> My last piece of advice is that the R-390A is a modular radio. Don’t try to
> do everything at once. Work on it one module at a time. Start with the power
> supply if you are going to replace the 35W4s with solid state rectifiers.
> Then go on to the audio deck. Then the IF deck, which will take up the bulk
> of your time. The crystal oscillator comes next. Finally, the RF deck. After
> each stage is completed, plug the module back into the main chassis and make
> sure the radio still works! 
 
Good advice.  1 chassis at a time.  An unabashed plug here for W8RO's Hi-Res Communications video business.  If you're really doing to take this project on, get the R390A videos and learn some of the tricks.  It'll shorten your day quite a bit.  

Chuck Rippel
WA4HHG