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Vintage Collins Radio · r-390a.net
Collins KWM-2 / KWM-2A — Serial Number & Production Guide
VK6ADA Technical Reference · Collins Vintage Amateur Transceivers · March 2026 · Mike Peace VK6ADA
The Collins KWM-2 is widely regarded as the definitive HF SSB transceiver of the valve era — a landmark instrument that set the standard for performance, stability, and build quality from its introduction in 1959 through approximately 1980, a production run exceeding twenty years.[7] Covering 3.4–30.0 MHz across all HF amateur bands using an interchangeable coil assembly system, the KWM-2 combined the circuit architecture of the companion 75S-1 receiver and 32S-1 transmitter into a single compact chassis.[4] The KWM-2A followed with production improvements and was adopted extensively for MARS and military communications in the Vietnam era.[4] This guide consolidates serial number ranges, emblem era transitions, KWM-2 vs. KWM-2A identification, manual history, and restoration reference data.
Overview & Specifications
Manufacturer | Collins Radio Company — Cedar Rapids Division, Cedar Rapids, Iowa |
Model Designations | KWM-2 / KWM-2A (improved production variant; factory upgrade kit also available) |
Production Period | ~1959 (KWM-2) — approximately 1979–1980 (KWM-2A final production) |
Type | SSB/CW HF Transceiver; mobile or fixed station; external power supply required |
Frequency Coverage | 3.4–30.0 MHz — all HF amateur bands (80m through 10m); 200 kHz coverage per coil assembly[4] |
RF Power Input | 175 W PEP SSB / 160 W CW[1] |
RF Power Output | 100 W PEP nominal[1] |
Modes | USB, LSB, CW (sidetone monitoring); VOX; ALC |
IF Architecture | Double conversion: HF IF 2.955–3.155 MHz (crystal-controlled); LF IF 455 kHz (VFO-controlled); Collins Mechanical Filter at 455 kHz[4] |
Receiver Sensitivity | 0.5 μV for 10 dB S/N ratio[1] |
Receiver Selectivity | 2.1 kHz at 6 dB down; 4.2 kHz at 60 dB down[1] |
Frequency Stability | < 100 Hz per hour drift — exceptional for the era[4] |
Frequency Resolution | 1 kHz dial divisions on all bands[1] |
Tube Complement | 18 tubes: 6AZ8 (×3), 6U8A (×4), 12AT7 (×2), 6DC6, 7543, 6CL6, 6146A (×2), 6BN8 (×3), 6EB8[4] |
PA Tubes | 2 × 6146A (parallel pair) |
VFO | Collins 70K-2 Permeability-Tuned Oscillator (PTO) — slug-tuned rack |
Calibrator | 100 kHz crystal calibrator built in |
ALC | Automatic Load Control on IF and RF stages; up to 10 dB compression[1] |
Power Supply | Collins 516F-2 (heavy duty, recommended) or PM-2 (limited duty cycle) — external required[4] |
Emblem Eras | All four Collins emblem eras represented across the 20+ year production run |
Military / MARS Use | KWM-2A widely used by MARS stations in Vietnam; military and government deployments[4] |
Important Note on Serial Number Sequencing
⚠ Randomised Serial Number Assignment — Collins Policy
Collins Radio issued serial numbers for the KWM-2/2A in randomised (non-sequential) order, consistent with Art Collins’ documented decree that serial numbers should not convey production date information.[9] CCA survey research by Rod Blocksome K0DAS has confirmed the existence of missing serial number blocks and a scrambling methodology within the KWM-2/2A production record.[5] For the most reliable production date estimate, examine the date codes stamped on IF cans and other fixed components inside the chassis (format: YY MM). The emblem type provides the broadest era indicator.
Collins Radio issued serial numbers for the KWM-2/2A in randomised (non-sequential) order, consistent with Art Collins’ documented decree that serial numbers should not convey production date information.[9] CCA survey research by Rod Blocksome K0DAS has confirmed the existence of missing serial number blocks and a scrambling methodology within the KWM-2/2A production record.[5] For the most reliable production date estimate, examine the date codes stamped on IF cans and other fixed components inside the chassis (format: YY MM). The emblem type provides the broadest era indicator.
Collins Logo / Emblem Production Eras
With a production run exceeding twenty years, the KWM-2/2A spans all four Collins emblem eras. The front-panel emblem is the fastest single indicator of approximate production period, though due to random serial number assignment it must always be cross-referenced with internal component date codes for reliable dating.[5]
✔ Best Dating Method for KWM-2 / KWM-2A
Component date codes stamped on IF cans and similar fixed components inside the chassis are the most reliable single dating indicator. Format is typically YY MM (year then month). A unit with IF cans stamped “74 11” was manufactured no earlier than November 1974. Cross-reference with the front-panel emblem for confirmation.[6] The 70K-2 PTO serial number is an additional secondary dating reference when correlated with the CCA PTO serial number survey.[5]
Component date codes stamped on IF cans and similar fixed components inside the chassis are the most reliable single dating indicator. Format is typically YY MM (year then month). A unit with IF cans stamped “74 11” was manufactured no earlier than November 1974. Cross-reference with the front-panel emblem for confirmation.[6] The 70K-2 PTO serial number is an additional secondary dating reference when correlated with the CCA PTO serial number survey.[5]
| Emblem Type | Approx. Period | Approx. S/N Zone | Physical Description | Collector Notes |
|---|---|---|---|---|
| Winged Emblem | ~1959 – Fall 1969 | Low ranges; see note on random assignment | Stylised red winged device; “COLLINS” below; upper-left front panel | Most desirable to purists; full 10+ year Winged-era production of KWM-2; cleanest vintage presentation |
| Round Emblem | ~Fall 1969 – ~1974 | Overlapping ranges — not deterministic | Round red disc; white “Collins” script logo | Transition era; both KWM-2 and KWM-2A units found; S/N 14862 and S/N 18355 are documented Round Emblem KWM-2A examples |
| Block / Italic Letter | ~1974 – ~1977 | Later production ranges | Block or italic “COLLINS” lettering without winged or round device | Post-Rockwell acquisition era styling; plastic trim and revised knobs often present |
| Late / Rockwell Era | ~1977 – ~1979/1980 | Latest production ranges | Rockwell International Collins branding variants | Final production run; represents the end of the classic Collins amateur equipment era |
Serial Number Lookup Tool
Enter a KWM-2 or KWM-2A serial number for an estimated production era. All results are indicative only, given the documented random S/N assignment and missing S/N blocks in the CCA survey record.
KWM-2 vs. KWM-2A — Identification Guide
ℹ Factory Built vs. Factory Converted — Identification
Collins offered a factory kit to upgrade KWM-2 units to KWM-2A specification. The key identification difference on the front panel is the EXCITER TUNING and PA TUNING controls: a continuous thick line on these controls indicates a factory-built KWM-2A. Upgraded (converted) KWM-2 units may not show this marking. Additionally, factory-built KWM-2A units carry the model designation stamped on the chassis serial number tag; converted units may show hand-written notation rather than a machine stamp.[6]
Collins offered a factory kit to upgrade KWM-2 units to KWM-2A specification. The key identification difference on the front panel is the EXCITER TUNING and PA TUNING controls: a continuous thick line on these controls indicates a factory-built KWM-2A. Upgraded (converted) KWM-2 units may not show this marking. Additionally, factory-built KWM-2A units carry the model designation stamped on the chassis serial number tag; converted units may show hand-written notation rather than a machine stamp.[6]
| Feature | KWM-2 | KWM-2A |
|---|---|---|
| Front-panel designation | “KWM-2” | “KWM-2A” |
| EXCITER / PA TUNING marking | Standard marking | Continuous thick line on tuning controls (factory-built only) |
| Chassis serial tag | Stamped | Stamped (factory); hand-written annotation possible on converted units |
| Frequency coverage | 3.4–30.0 MHz | 3.4–30.0 MHz; some military units extended beyond amateur bands |
| Military / MARS deployment | Some use | Extensive — MARS stations in Vietnam; U.S. military and embassy use[4] |
| Circuit differences | Original design | Minor AGC refinements; dial lock added; weighted tuning knobs; HT interlocks — circuit substantially similar over 20-year run[8] |
| Escutcheon | KWM-2 engraving | KWM-2A engraving (primary factory conversion component) |
| Emblem eras | Winged, Round (early production) | Winged, Round, Block, Late — depending on year of manufacture |
| Conversion kit | Could be upgraded to 2A spec via factory kit | N/A (factory production or field conversion) |
Documented Serial Numbers
| Serial Number | Model | Emblem | Approx. Year | Notes / Source |
|---|---|---|---|---|
| ~10360 | KWM-2 | Winged | 1959–1960 | French collector report (CCAE); dated by serial number context and owner account[3] |
| 14862 | KWM-2A | Round | ~1970–1974 | Listed with MCN 9776 and 70K-2 PTO S/N 52054; plastic trim, screw-type knobs; documented in collector records[10] |
| 18355 | KWM-2A | Round | ~1970–1974 | Collector listing; Round Emblem confirmed[10] |
| Various (end-of-1974 range) | KWM-2A | Block/Italic | Late 1974 | EB5AGV’s unit; dated by IF can component date codes stamped “74 11” (November 1974)[6] |
📋 Additional Serial Number Data Wanted
Rod Blocksome K0DAS has specifically identified the KWM-2/2A as needing additional survey data to better define missing serial number blocks and total production numbers — as well as 70K-2 PTO serial numbers to correlate with KWM-2/2A and S-Line units.[5] Contact the Collins Collectors Association via collinsradio.org.
Rod Blocksome K0DAS has specifically identified the KWM-2/2A as needing additional survey data to better define missing serial number blocks and total production numbers — as well as 70K-2 PTO serial numbers to correlate with KWM-2/2A and S-Line units.[5] Contact the Collins Collectors Association via collinsradio.org.
Compatible Accessories & Station Equipment
| Accessory | Collins Model | Notes |
|---|---|---|
| Power Supply (heavy duty) | Collins 516F-2 | Recommended for sustained operation; 115 V AC; matches KWM-2/2A chassis styling |
| Power Supply (light duty) | Collins PM-2 | Limited duty cycle — suitable for intermittent operation only[4] |
| Speaker / Station Console | Collins 312B-4 | Matches KWM-2/2A cabinet styling; includes phone patch and S-meter |
| Linear Amplifier | Collins 30L-1 | Standard pairing for full KWM-2/2A station; 4 × 811A tubes, 1 kW PEP |
| External VFO | Collins 321B-5 | Second VFO for split-frequency DX operation |
| Wattmeter | Collins 302C-3 | In-line wattmeter compatible with KWM-2/2A station |
| Mobile mounting | Collins mobile rack tray | For vehicle installation; KWM-2/2A in Samsonite Silhouette cases documented for government/diplomatic use[11] |
Manual & Documentation History
| Document | Description | Notes |
|---|---|---|
| KWM-2 / KWM-2A Instruction Book | Factory manual covering operation, alignment, and parts list; multiple editions reflecting circuit revisions | BAMA archive; CCA Technical Archives; consult edition date for circuit revision reference |
| Technical Bulletin supplements | Factory-issued TB sheets covering AGC updates, relay improvements, HT interlock additions, and other running changes | CCA Technical Archives; recommended reading before any alignment work |
| AIR PUBLICATION 116E-0128 | Military KWM-2A technical publication (TGRI AT 23183/I); covers military-specific configurations | Scanned by F5TEV; available via CCAE (European Collins Collectors Association)[3] |
| CCA Technical Archives | Supplemental articles, restoration notes, CCA Journal back-issues | collinsradio.org |
| CCAE Tools & Resources | French/international KWM-2/2A documentation, schematics, wiring diagrams, modification notes | ccae.tm6cca.com[3] |
Circuit Notes & Restoration Considerations
| Item | Notes |
|---|---|
| Thermal management | The KWM-2/2A runs warm — especially the PA cage and surrounding components. After 50+ years, cooling fan additions (aftermarket kits available) are strongly recommended for sustained operation. Heat damage to nearby components is a common fault in non-fanned units.[3] |
| 70K-2 PTO alignment | The PTO is the heart of the KWM-2/2A. The slug-tuned rack must be carefully realigned if disturbed. Do not over-tighten the rack. See detailed PTO alignment procedure in CCA technical articles. |
| CW sidetone compromise | The KWM-2/2A uses a 1500 Hz tone oscillator for CW sidetone generation — the transmitted CW frequency will be 1500 Hz above the dial reading.[4] Carrier-generated CW modification articles exist and are well documented in CCA literature. |
| 6146A PA pair | Match the PA pair for plate current balance. 6146B is the preferred modern substitute. Avoid 6146W (mil-spec variant with different pinout). Check cathode resistors and screen supply stability. |
| Mechanical Filter | 455 kHz Collins MF; robust if undamaged. Test selectivity shape carefully — a degraded MF shows a rounded passband. Spares are increasingly scarce; handle with care. |
| ALC alignment | ALC loop gain and threshold are critical for clean SSB — misaligned ALC is a common cause of splatter. Follow factory alignment procedure precisely, particularly the IF chain before ALC loop closure. |
| On/Off switch | Switch failure is a known failure point in aged KWM-2/2A units. Repair/rebuild kits and procedures are available via CCAE resources.[3] |
| CR7 diode | The CR7 diode is a known failure component in KWM-2/2A circuits — confirm availability before undertaking full restoration.[3] |
| Component dating via IF cans | Stamped date codes on IF transformers (format YY MM) are the most reliable production dating method. Record all codes found and compare with front-panel emblem for cross-validation.[6] |
| Capacitor replacement | Wax-coated paper capacitors throughout; electrolytic capacitors in power supply and audio sections. Full recap is standard practice before alignment. |
| MARS / military KWM-2A | Military-deployment examples may show non-standard crystal complements, modified frequency coverage, or external relay control wiring. Verify configuration before alignment. |
References
- Collins Radio Company. KWM-2/2A Transceiver Technical and Instruction Manual. Cedar Rapids, Iowa. Reproduced at CCA Historical Archives. collinsradio.org.
- Johnson, Gerald K0CQ. Collins Serial Numbers (mailing list post, June 2004). QTH.net Collins Reflector. qth.net.
- CCAE — European Collins Collectors Association. KWM-2/2A Tools and Resources. ccae.tm6cca.com.
- Electronics Notes. Collins KWM-2 Vintage Ham Radio Transceiver. electronics-notes.com.
- Blocksome, Rod K0DAS. Collins Radio Production Surveys — KWM-2/2A. Collins Collectors Association Technical Archives. collinsradio.org.
- Gavila, Jose (EB5AGV). KWM-2A Pictures and Notes (includes IF can dating method and factory-built vs. converted identification). jvgavila.com.
- CCA groups.io. KWM-2A — Production and Circuit Changes Discussion (August 2023). groups.io.
- K9ZW. Collins KWM-2A Station (blog; includes Round Emblem and Winged Emblem station comparisons). k9zw.wordpress.com.
- QTH.net Collins Reflector. Collins Serial Numbers — Random Assignment Policy (July 2005). qth.net.
- Collins Radio Transceiver archive. KWM-2A Collector Listings (S/N 14862, S/N 18355 documented). hamradiotransceiver.biz.
- Collins Radio Company. Collins Guidebook and Notes (1994). KWM-2 in Samsonite Silhouette case; mobile and diplomatic deployment. worldradiohistory.com.
- WA3KEY Virtual Collins Radio Museum. Collins equipment reference pages. wa3key.com.
- VK6ADA. Collins Vintage Radio Reference Collection. vk6ada.com.au · r-390a.net.