Rebuilding R-390A Power Supply Caps. Step by Step With Photos

Discussion in '"Boat Anchor" & Classic Equipment' started by KC8VWM, Apr 16, 2016.

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  1. KC8VWM

    KC8VWM Ham Member QRZ Page

    Tell you what.... :)

    I'll take the 110w VHF Spectra with the HH control head and I will even send you out another NOS meter in it's original box, replacement glass to fix the meter you already have, send some printed and optimized meter scales on cardstock paper, and even some extra cardstock printed scales just in case, and this will give you two working and matching sets of R-390A meters in trade instead of sending me any mullah.

    ....Whadda say?
    Last edited: Jun 5, 2016
  2. N3DT

    N3DT Ham Member QRZ Page

    Charles, I sent you email.
  3. KC4DYM

    KC4DYM Ham Member QRZ Page

  4. KC4DYM

    KC4DYM Ham Member QRZ Page

    Charles great thread .
    Hope you are happy you motivated to dig my R390A after
    20 yrs in storage also had cigar box of caps orange drops Sp rage caps 20 yr shelf life ?????

    73 Ray
    KC8VWM likes this.
  5. KC8VWM

    KC8VWM Ham Member QRZ Page

    This used to be your R-390A?

    What can you tell me about it? ...Where did it come from?
  6. KC4DYM

    KC4DYM Ham Member QRZ Page

    Radio is Motorola 1954 has top and bottom covers also meters that glow in dark has vernier bfo dial (RITTY )
    Came from Mars operator about 1984 it worked till 9os when I put in storage do not know if has any mods '
    Never been into it .Do you think od caps ok to use .
    73 Ray
    KC8VWM likes this.
  7. KC8VWM

    KC8VWM Ham Member QRZ Page

    Yeah sure Ray. If you already have OD's, just use them.

    I just found they are very large and sometimes difficult to fit into tight spaces.
    The smaller box caps I am using serve the same purpose and their specifications are superior to the original Vitamin Q's.
  8. KC8VWM

    KC8VWM Ham Member QRZ Page

    This will describe striping the white lines on the knobs of the R-390A but it could apply to any kind of radio knobs.

    There's a few different ways to do this. A needle tipped paint pen can be used to fill in the lines on the knob, but even using this fine precision way of doing things can sometimes result in the paint ending up outside the line and on the knob anyways. This will require you to clean off any undesired and remaining paint residue from the knob.

    The best and fastest way it to forget about expert precision, steady hand and the tedious task of trying to individually paint every single knob just perfectly. I use the "paint and wipe" method instead and the final results as you are about to see will be identically the same.

    The most universal way to paint them is to simply apply paint using a fine tipped paint brush. The method used is to simply apply paint to fill in the line on the knob and then wipe away the unwanted paint from the knob. I call this method "paint and wipe" The final result will be absolutely perfect.

    However the paint and wipe method should only be done with newly painted knobs where the paint has cured. I will only stripe the knobs using this method after waiting about 7 - 14 days after the knobs have been painted.

    The items you will need is paint, an assortment of fine tipped artist brushes, ($3.50 for the whole package of brushes seen below) some of them blue shop towels and a bottle of rubbing alcohol.



    The type of paint you choose for doing this is very important. You want to choose a water based acrylic paint. The reason you want to choose this kind of paint is because if you do make any mistakes, the paint is water based and therefore it can be washed away and you can simply start over again.

    Most "hobby" sections of many department stores will carry a wide and economical assortment of various paints suitable for this purpose.


    I like using this particular water based acrylic paint because it's somewhat thick in consistency like Elmer's glue. When using it, it works and applies to the knob more like a "paste" than a thin runny paint. It easily and entirely fills in the line on the knobs.

    Simply apply paint to the line on the knob using the brush. The objective here is to simply "fill in" the line with paint.


    When completed the paint will look like this on the knob. As you can see in the photo below we are not particularly concerned with how "accurate" the paint is applied to line on the knob. We are only concerned with filling in the line with paint.


    Next is the "wipe" after the paint. I use rubbing alcohol because it removes the residue much, much easier than using water. You can certainly use water but this may require you to rub the knob harder to remove the excess paint from the knob. For example, using water requires 2 or 3 wipes, whereas using rubbing alcohol can often do this in a single 1 wipe pass. Basically, rubbing alcohol simply does a much better job of this with minimal effort involved. It does not damage the black paint finish on the knob if the paint has been left to cure on the knob.

    When wiping the excess paint from the knob, you are avoiding the idea of pulling the paint away from inside the line of the knob. So the less you wipe it, the better. :) When you get good at doing this, you will find you can wipe it entirely clean in a single pass very quickly and with minimal effort.


    If a single pass doesn't do the job, then with the bulk of the paint removed from the knob, simply finish up by removing any residual paint left on the knob with another blue shop towel dampened with rubbing alcohol.


    When completed the knob will end up looking like this:


    Now do this to all the knobs and place them back on the R-390A :)


    Don't worry if you mess it up, just wash the paint off the knob with water and start over again. :)

    Incidentally, the very same "paint and wipe" method can also be used to restore the faded engraved lettering on the front panel of the R-390A. Stay tuned for that chapter. :)

    Attached Files:

    Last edited: Dec 28, 2017
  9. KC4DYM

    KC4DYM Ham Member QRZ Page

    The pipe cutter did not work because of lip on bottom cap Can not keep it strait .

    AF6LJ likes this.
  10. KB4MNG

    KB4MNG Ham Member QRZ Page

    Knobs look really good...
    KC8VWM and AF6LJ like this.

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