The R-390A/URR is a general-coverage military HF communications receiver covering 500 kHz to 32 MHz across 32 one-megahertz bands. It was designed by Collins Radio Company as a cost-reduction successor to the R-390, entering production in 1955 and remaining in manufacture until 1984 — a 29-year production run across seven contractors and over 55,000 units. It served in all branches of the US Armed Forces, the CIA, and the NSA throughout the Cold War and beyond.

Where the R-390 used L-C IF filtering and a welded chassis, the R-390A uses Collins mechanical filters for the narrow IF bandwidths and a modular construction with pull-out sub-assemblies. This modularity makes the R-390A significantly more accessible for cosmetic restoration than the R-390.

Restoration Phases

Unlike the R-390 which was built by Collins only, the R-390A was produced by seven contractors over its production life. Each manufacturer applied the same MIL-F-14072 P513F finish specification, but minor variations in colour tone and finish sheen exist between manufacturers and production runs. A receiver assembled from modules made by different contractors — known as a “mongrel” — is common and carries no stigma. It is a positive testimonial to the interchangeability of the design.

CCA grading applies to the R-390A as it does to all Collins-designed equipment. Given the very large production numbers, Mint and Excellent examples are more achievable than with the rarer R-390. A quality cosmetic restoration with correct panel markings and original hardware can reach Very Good, which is the ceiling for any repainted unit.

Source: collinsradio.org — CCA Grading Standards

The R-390A’s modular design makes disassembly more straightforward than the R-390. The major sub-assemblies — RF deck, IF deck, Audio/VR deck, PTO, Power Supply, and Calibrator — each pull out independently on slides or mounting screws. There is no green gearwheel procedure required; the R-390A’s mechanical synchronisation system handles module removal differently.

Knob Removal

1. 1R-390A knobs use Bristol (splined) setscrews. Use the correct Bristol wrench — a hex key will damage the splined socket. Loosen, do not remove fully.
2. 2The main tuning knob is held by a clamp around a split shaft, not a setscrew — consult TM 11-5820-358 for the correct removal procedure for this specific knob.
3. 3Pull all other knobs straight off their shafts. Label and bag each by panel position.
4. 4Remove the S-meter and carrier level meter pointers with a thin plastic spudger. Both pointers are fragile and irreplaceable.

Front Panel Removal

1. 1The front panel is secured by machine screws around its perimeter — JIS type. Label all inter-panel connectors and wiring before disconnecting.
2. 2The bandswitch shaft and several control shafts pass through the panel. Release the bandswitch shaft coupling before drawing the panel forward.
3. 3Set the panel face-down on foam padding. Protect the dial glass and meter glasses.

Sub-Assembly Removal

1. 1Remove sub-assemblies in the sequence specified in TM 11-5820-358. Each module is held by a specific combination of mounting screws and/or slide rails.
2. 2Remove and discharge the Power Supply fully before handling — use a bleeder resistor, not a screwdriver short.
3. 3Remove the PTO carefully — do not adjust PTO calibration during cosmetic work. The PTO calibration is a separate alignment procedure in the TM.
4. 4The RF deck contains slug racks with fragile ferrite slugs. Do not drop the deck or allow the slug racks to contact hard surfaces during handling.
5. 5Label all connectors and harness runs as sub-assemblies are removed. The R-390A has numerous inter-module connections that are not always obviously labelled.

The R-390A cleaning approach is the same as the R-390: Formula 409, water rinse, and distilled water final rinse on the chassis and sub-assemblies. The same community-documented procedure applies (Chuck Rippel, R-390A Owners Manual; Dave Medley, r-390.com). The front panel again requires the scuff-and-paint approach due to the hard baked enamel.

Chassis & Sub-Assembly Cleaning

1. 1Spray the bare chassis thoroughly with Formula 409. Scrub with 0000 fine steel wool. The zinc-coated baseplate will come up clean and shiny.
2. 2Rinse with a garden hose. Follow with a distilled water rinse to remove tap water mineral residue.
3. 3Dry thoroughly with a hair dryer. Any trapped moisture causes corrosion.
4. 4Repaint any painted chassis areas — scuff with steel wool and apply haze gray topcoat. The zinc baseplate does not receive paint.
5. 5Apply the same 409 / hose / distilled water / dry sequence to each sub-assembly separately. The RF deck requires special attention — consult the r-390a.net archive for RF deck cleaning procedures before starting on this module.

Front Panel — Baked Enamel

1. 1Clean the panel surface with 409 and a soft cloth. Remove all grease and grime.
2. 2Scuff the entire panel surface with 0000 fine steel wool to break the gloss.
3. 3Wipe with 99% IPA followed by acetone. Tack-clean.
4. 4Apply two thin-to-medium coats of haze gray topcoat. The panel legends will be painted over and restored using the lacquer stick technique after topcoat cures — see Section 11.

Bandswitch Contacts

The R-390A bandswitch is a known contact cleanliness point. Apply DeOxit D5 to all bandswitch contacts during disassembly. Do not use abrasive contact cleaners on the bandswitch — the contacts are plated and abrasion damages the plating.

Surface preparation on the R-390A follows the same principles as the R-390. The front panel is aluminium; the chassis and cabinet are steel. Treat each substrate appropriately.

Dent Repair

Minor dents in the front panel or cabinet respond to hammer-and-dolly technique from behind. Apply Evercoat Metal Glaze finishing putty to remaining low spots, sand to 220 grit, prime. Deep creased dents are not practically repairable at bench level — disclose them.

Non-Original Hole Filling

Field modification holes are common in R-390A units. Fill from behind with a small aluminium patch bonded with PC-7 epoxy, fill proud from the front with Metal Glaze, sand flush. Prime before topcoat.

Corrosion Treatment

Treat all rust with Ospho phosphoric acid converter. Allow to dry to white residue, then prime immediately. Galvanic corrosion at aluminium-to-steel interfaces (rack ear mounting points) should be treated with zinc chromate primer on the contact surfaces before reassembly.

Final Cleaning Before Topcoat

1. 1Wipe all surfaces with 99% IPA on a lint-free cloth. Flash off 2 minutes.
2. 2Follow with an acetone wipe to remove silicone contamination.
3. 3Tack-wipe lightly. Prime bare metal areas within 30 minutes.

As with the R-390, primer is required on bare metal areas only. The front panel over the scuffed baked enamel does not require primer — the scuffed surface provides sufficient mechanical adhesion.

• Self-etching primer on bare steel: SEM Self-Etching Primer or 3M 05917 — 2 light coats, do not sand
• Zinc chromate primer on aluminium-to-steel contact surfaces at rack ears
• High-build 2K surfacer over body filler repairs: USC Spray Max 2K — 3 coats, cure, sand to 320 grit
• Allow full primer cure (minimum 2 hours) before topcoat
• The front panel over scuffed enamel: no primer required

The R-390A front panel finish is specified in the engineering drawings (e.g. SM-D-283246) as finish P513F per MIL-F-14072, the military specification for finishes for ground-based electronic equipment. This finish is commonly described as haze gray — a standard military gray. The same specification applies across all manufacturers; minor variation between contractors and production years is expected in surviving examples.

The R-390A front panel takes a baked enamel topcoat — not a wrinkle or texture product. Application follows the same technique as the R-390: two coats maximum on the front panel to preserve legend recess depth for the lacquer stick marking technique.

Front Panel Application

1. 1Mask the dial glass, both meter glasses, and all bezel hardware with fine-line tape doubled with painter’s tape.
2. 2Apply a thin first coat — to seal and provide a base, not full coverage. Allow 30 minutes flash time.
3. 3Apply a second medium coat for full coverage. Allow 24 hours cure before the lacquer stick marking step.
4. 4Do not apply a third coat over the panel legends — this fills the recesses and makes marking restoration ineffective.

Chassis Painted Areas & Rack Ears

Painted areas on the chassis, internal brackets, and rack ears receive the same haze gray topcoat as the front panel. Scuff with steel wool, clean, and apply two medium coats. The zinc-coated baseplate does not receive paint.

R-390A front panel markings are engraved or embossed legends filled with white paint, allowing the same lacquer stick technique used on the R-390. The technique was documented for the R-390A by Chuck Rippel in the R-390A Owners Manual and is the standard community method.

Lacquer Stick Technique (Engraved Panels)

1. 1Allow topcoat to cure fully — minimum 24 hours. A partially cured topcoat will lift when the lacquer stick is applied.
2. 2Draw a white lacquer stick firmly across the panel surface, working in sections. The lacquer fills the engraved legend recesses.
3. 3Before the fill hardens (5–10 minutes working time), wipe the flat surface with a soft cloth barely dampened with lacquer thinner. The fill in the recesses is protected by the engraving geometry.
4. 4Inspect under a magnifier. Repeat fill-and-wipe for incompletely filled legends.
5. 5Allow 24 hours cure before sealer coat.
6. 6Apply one thin coat of Testors Dullcote from 12 inches to seal the markings.

Data Plates & Module Tags

Each R-390A sub-assembly carries a module identification tag showing the manufacturer, contract number, and date. These tags are important provenance elements — do not overpaint them. If the front panel data plate is missing, reproduction plates are available from community vendors; the manufacturer and contract data should match the known production history of that serial number range.

Knob Restoration

R-390A knobs are black phenolic or Bakelite — do not repaint them. Clean with mild soap and a soft brush. Polish with Novus Plastic Polish #2 followed by #1. White indicator grooves in knobs can be restored with a white lacquer stick using the same technique as the panel markings.

IERC Tube Shields

IERC tube shields are a significant performance item for the R-390A. The correct shields are anodised black (or deep purple), have an open top with tabs folded over a thin octagonal metal insert, and grip the tube bottle to conduct heat away. Incorrect replacements — plain shiny shields or painted black shields without the grip insert — do not provide heat sinking. According to Collins Radio’s own study, correct IERC shields increase tube life by up to 53%.

• The R-390A uses three sizes: short 7-pin, regular 7-pin, and regular 9-pin
• If your unit has plain shiny or painted-black shields, replace them with correct IERC type
• IERC shields appear at hamfests and on eBay — they have become more expensive as tube enthusiasts recognise their value
• Do not use the “ovens” switch on the rear panel — it causes the receiver to drift and can permanently damage the PTO thermostat

Mini BNC Internal Connectors

The R-390A uses miniature BNC connectors for internal coax — a known frustration compared to the standard BNC in the R-390. Clean mini BNC bodies with 99% IPA; polish contacts with Flitz Metal Polish on a cotton swab. Replace only if the centre pin is damaged or the connector body is cracked.

Rack Hardware & Fasteners

• Original rack mounting screws are 10-32 cadmium-plated — replacements from Fastenal or Grainger
• Rack ears receive the same haze gray P513F topcoat as the front panel
• Replace deteriorated gasket strips behind rack ears with 1/16″ closed-cell neoprene foam tape
• Original cadmium-plated fasteners are preferred over modern stainless replacements — clean with brass brush and Flitz before deciding to replace

PTO — Collins vs Cosmos

R-390A PTOs come in Collins and non-Collins (typically Cosmos Industries) varieties. Community assessment of Cosmos PTOs is nuanced — there are two types within the Cosmos production, primarily distinguished by end-to-end accuracy. Identification is by decal. For cosmetic restoration purposes, the PTO type does not affect the finishing procedure, but it should be documented for any CCA listing.

1. 1Reinstall sub-assemblies in reverse order of removal per TM 11-5820-358. Verify each module is fully seated and locked before proceeding to the next.
2. 2Reconnect all inter-module wiring harnesses per your labelled documentation. Route harnesses exactly as original.
3. 3Fit the front panel, engage the bandswitch shaft coupling, and tighten perimeter screws with a JIS driver.
4. 4Install knobs to labelled positions. Tighten Bristol setscrews snugly on shaft flats. Install the main tuning knob per the TM clamp procedure.
5. 5Install meter pointers last — press straight onto the spindles with no tools.
6. 6Install rack ears with original or replacement 10-32 screws.

CCA Grade Self-Assessment

Evaluate the completed restoration under natural daylight. R-390A-specific assessment points:

• Panel markings — all legends present, white, filled into recesses, no excess on flat surface
• Haze gray consistency — front panel, chassis painted areas, and rack ears visually consistent
• All module identification tags present — not overpainted
• IERC tube shields — correct type, not plain-shiny replacements
• Knobs — correct type for R-390A, indicator grooves filled white
• Hardware — original cadmium-plated fasteners where possible
• Zinc baseplate — clean and unpainted
• Restoration disclosed — any repainting must be identified in CCA listings