The R-390A Frequently Asked Questions Page
This document is a compilation of the wisdom shared by members of the online community of R-390A enthusiasts.  As such, it is advice to those who endeavor to maintain and restore the R-390A family of receivers.

The information is shared without warranty, expressed or implied. This information is in the public domain and can be freely copied or shared.

Appropriate attribution is appreciated.
1.1 - Removing Paint Overspray

    Lacquer thinner can be used to remove some types of paint overspray from
    the surface of enamel paints, such as are found in the original R-390A
    panels.  Use a soft cloth and lots of 'elbow grease' to remove paint
    overspray without affecting the gray enamel or the white lettering.  

    CAUTION: The orange military inspection markings are much less
    resistant to paint thinners.  They are relatively easy to
    'accidentally' remove using most paint thinners or solvents.

1.2 - Surface Cleaning

    Before cleaning any surface, test the proposed cleaner in an
    inconspicuous spot to ensure that it will not harm the finish.

    An automobile paint polish intended for oxidized paint can remove
    surface 'dinginess' and brighten up the panel.  Do not use any polish
    that claims to 'cut' the surface - they are too harsh and will probably
    dull the finish.

    Use of "Goof-Off" or similar Xylene based products requires some
    caution.  The label states that it is useful for removing "latex" paint
    from "fully cured varnished and oil-based painted surfaces".  In other
    words, it can remove latex paint from enamel painted and varnished
    surfaces.  It usually will not remove enamel paint.  It may seriously
    harm plastics if it comes in contact with them.

    Some folks report good cleaning results when using "GoJo' hand cleaner,
    the kind that does not contain pumice.

1.3 - Surface Maintenance

    If you choose to polish the surface with wax or similar products,
    several caveats have been posted by list members:

     - Use of Armor-All or similar silicone bearing products will leave
       a nice sheen, but render it nearly impossible to repaint without
       stripping the panel or knob.  It may also soften the paint.

     - WD-40 evaporates in a few weeks and leaves a dull finish behind,
       requiring frequent retouching.

    Several people seem to like 'Tannery' leather and vinyl care products. 
    They are available in both spray and creme forms.
2.1 - Chemical Stripping

    Several chemical strippers have been used successfully to remove paint
    from the panel and knobs on the R-390A.  
     - JASCO stripper

2.2 - Mechanical Stripping

    Some folks have reported good results when using a fine wire brush
    attached to an electric drill or 'Dremel' tool.  Use a dust mask,
    as the composition of the paint(s) you are removing is unknown.  After
    all paint is removed, wash the surface to remove any remaining residues.

2.3 - Aluminum Surface Preparation

    After removing all of the paint, sand out any imperfections using
    240 grit or finer sandpaper.  NEVER use steel wool, as it embeds bits
    of steel into the aluminum surface, which protrude from the surface and 
    will eventually rust, marring the finish.

    Bare aluminum requires surface preparation before painting.  Several 
    chemical cleaners are available which etch the surface.  many of them
    require the use of rubber gloves and plenty of ventilation for their 
    safe use.  Pay close attention to any instructions and warnings 
    associated with the package before beginning the process.

     - Alumiprep 33 "Cleaning and Conditioning Chemical for Aluminum"
     - DuPont 226S Conversion Coating
     - Duro (Loctite) Aluminum Jell Cleaner

    Work patiently and slowly and let the stripper do its work.  Use
    an old toothbrush or toothpick to 'scrub' the engraving.  Several
    applications of the stripper chemical may be required.

    If you are hesitant about using chemical strippers, The surface can be
    sanded with fine sand paper.  Then wash it with water to remove any
    residue, followed by a rinse with alcohol. Then household ammonia can 
    be used to remove any remaining grease. 
Paint Selection
    There does not appear to be a consistent 'right' color to use when
    refinishing the panel and knobs on the R-390A.

    Production R-390A receivers have appeared with front panels in shades of
    gray ranging from light gray to a dark blue-gray.  Many different shades
    of grey appear on both military and civilian refurbished units.  

    There are reports that the U.S. Air Force repainted some of their
    receivers flat black to match other air-ground radio equipment.  Canadian
    forces units reportedly painted their radios a light blue to match other 
    equipment in use.  Some receivers that were refinished by the U.S. Navy
    have a grey-green cast to their panel color that matches some other navy

    Enthusiasts have painted their receivers a wide range of colors including
    shiny black, forest green, and incredibly - red. One receiver panel was
    completely stripped, given a  turned' metal finish, re-lettered in black, 
    and then clear coated! 

    The original procurement specification for the R-390 (non-A) dated 28
    Aug 1950 as amended 28 Aug 1952 calls for the front panel to be
    "semi-gloss, non-wrinkle, gray enamel of a shade conforming to No. 2610
    of Federal Specification TT-C-595".

    R-390A Front Panel Drawing SM-D-283246 Revision 2, 3-Mar-60 calls for
    the panel surface to be "Finish P513F per Spec. MIL-F-14072".  It also
    calls for filling the engraving with "White, color chip #27875 per Fed.
    Std. 595". 

    Military Specification MIL-R-13947B(SigC) dated 26 October 1960, in
    section 3.9 states "The final paint film on Type I surfaces shall be
    final film E, semigloss, light-gray enamel, conforming to MIL-F-14072".

3.1 - Primer
    Because bare aluminum oxidizes so quicky, an etching primer is preferable, usually
    zinc oxide or zinc chromate based.  Other primers are not as reliable in providing
    good paint adhesion. 
     - Zinc oxide or zinc chromate based primers, found mostly in marine or aviation 
       supply houses
     - Rustoleum white or gray primer (not zinc-based)
     - latex based automotive primer
     - "DAP Primer", followed by light sanding with 1500 grit sandpaper

3.2 - Panel Finish
     - Rustoleum "Professional" #7587, "Dark Machine Gray"
     - PPG #55-307, "Battleship Gray"
     - Plastikote # 1105, "Medium Gray"

    If you desire to have a shiny finish, some claim that painting with a
    flat finish paint followed by application of a good wax looks better
    than using a gloss finish paint.

    Let the finish dry for at least 24 hours before touching it.

3.3 - Knob Finish
     - Rubberseal Products #RS-526 "European Trim Black" (matte)
     - Rustoleum #7777 "Satin Black"  
     - Sherwin-Williams DTM (Direct-to-metal) lacquer (custom mixed)
     - Krylon Epoxy #EP705 "Gloss Black"
     - Krylon #1613, "Semi-Flat Black"

    Rubberseal products are not widely available.   Their telephone number
    inside of Ohio is 513 890 6547 and outside of Ohio it is 800 257 6547.

3.4 - Engraved Lettering and Knob Striping
     - "White out" 
     - Acrylic Paint Stick
     - Bondex feather drywall patch

    Some report that artist's acrylic paint in a tube works well.  Some
    versions of the product have a very small nozzle opening, making
    application easier.  It remains water soluble until it is completely

    Some folks use white lacquer stick paint as sold by Antique Electronic
    Supply.  It has one drawback in its use - it never really hardens,
    remaining pliable and subject to 'adjustment' whenever it is
    accidentally touched.  

    If you thin the paint out a bit, a hypodermic needle can be used to
    apply paint to the knob striping and lettering.  Grind the tip of the
    needle off to a convenient angle.  Knob line painting can be done in two
    steps: 1) paint the line on the side of the knob with the knob resting
    on edge and 2) paint the line on the top of the knob resting on its
    back.  That way, the fluid never has to run downhill.  This technique
    does require a steady hand during application.
    Primer is applied in a very light coat, followed by one or more light
    coats of the final color.  It seems to work better to use several light 
    coats to achieve complete coverage rather than to continue spraying a
    piece until everything is well covered.

    Baking increases the durability of the applied paint.  Some opt to
    simply set the painted piece in the sun protected from bugs/dust by a
    layer of clear plastic suspended over it - like mosquito-netting. 
    Baking will create a deep gloss on enamel painted parts.  Semi-gloss or
    flat painted parts appearances are not enhanced by baking.

    A few of the more enterprising painters build a home made paint oven by
    screwing a heat lamp into a porcelain socket and placing it into a box
    that will retain the relatively low heat level (200 degrees or so)
    required to cure the paint.  The box can be constructed out of
    cardboard, plywood, or similar material.  Some have used an old
    refrigerator/freezer.  Place the work to be cured on a wire rack at
    least a foot-and-a-half (.5 meter) from the heat source.  A consensus
    seems to indicate that one is to avoid rapid temperature changes which
    can disfigure the surface through uneven heating/cooling.

    CAUTION:  Do not bake paint indoors.  The odors are noxious and very
    difficult to eradicate from indoor space.

4.1 -Panel Surface 
    One or more light coats of the final color, being careful not to allow 
    drips to form
4.2 - Panel Engraving
    Thin coats to avoid filling in the engraved letters

4.3 - Knob Surface
    Thin coats to avoid filling in the knob striping

    Mount the knobs on short pieces of dowel rod that protrude through a
    piece of cardboard.  

4.4 - Knob Striping
    - Apply white latex paint with a hypodermic needle.  
    - Allow it to dry for a few minutes and then wipe 'across' the stripe 
      using a damp cloth to remove any excess.  
    - After it is completely dry, use a 't-shirt' type cloth dampened in 
      mineral spirits or denatured alcohol to remove any 'shadows' of paint 
      that may remain around the stripe.

  • Allan Fritsche
  • Allen Tucholski
  • Andy Moorer
  • Barry Ornitz, WA4VZQ
  • Bill, wfw 'at'
  • Bob Ragain
  • Bobbi Barmore
  • Cal Eustaquio, N6KYR,
  • Charles Kembring, W8KXR
  • Craig McCartney
  • Dave Faria
  • Dr. Gerald N. Johnson
  • Ed Newman, WB2LHI
  • Gene Beckwith, W8KXR
  • Harry, KG5LO
  • Jan Skirrow, VE7DJX
  • Michael Crestohl, W1RC
  • Moret Denison
  • Paul Bock, K4MSG
  • Richard Biddle, KB5WLH
  • Rick Blank, KI5SL
  • Shaun Merrigan
  • Skip, skipperm 'at'
  • Tom Marcotte, N5OFF

Send Comments to the FAQ-Meister: (root[at]r-390a[dot]net)
Version: 6 - - Last revision: 2017-Dec-05