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Vintage Collins Radio · r-390a.net
Collins 75S-3 / 75S-3B / 75S-3C — Serial Number & Production Guide
VK6ADA Technical Reference · Collins S-Line Vintage Amateur Equipment · March 2026 · Mike Peace VK6ADA
The Collins 75S-3 SSB Receiver series is the definitive and most produced of the S-Line receivers, manufactured from approximately 1964 through the mid-to-late 1970s at the Cedar Rapids, Iowa facility.[1] Companion to the 32S-3 transmitter, the 75S-3 evolved through three main sub-variants (75S-3, 75S-3B, and 75S-3C), each reflecting incremental improvements to selectivity and AGC performance. The primary designer of the 75S-3 series was Dennis Day.[8] This guide consolidates serial number ranges, emblem transitions, sub-variant identification, and circuit variations to assist collectors and restorers.
Overview & Specifications
Manufacturer | Collins Radio Company — Cedar Rapids Division, Cedar Rapids, Iowa |
Model Numbers | 75S-3 / 75S-3B / 75S-3C (progressive sub-variants, same chassis) |
Primary Designer | Dennis Day — Collins Radio Cedar Rapids Engineering [8] |
Production Period | ~1964 – approximately 1977–1979 |
Receiver Type | Double-conversion superheterodyne with Collins Mechanical Filters |
Frequency Coverage | 3.4 – 30.0 MHz (amateur bands: 80, 40, 20, 15, 10 m) |
IF Frequency | First IF: 3.395 MHz (crystal filter); Second IF: 455 kHz (Mechanical Filter selectivity) |
Mechanical Filters (75S-3 base) | 500 Hz (CW), 2.1 kHz, 3.1 kHz — three-position filter selector |
Mechanical Filters (75S-3B / 75S-3C) | 500 Hz (CW), 1.0 kHz, 2.1 kHz, 3.1 kHz — four-position selector on 75S-3B and 75S-3C |
Modes | USB, LSB, CW, AM (envelope detector) |
Sensitivity (SSB/CW) | ≤ 0.5 µV for 10 dB S+N/N |
Mains Supply | 115 V AC or 230 V AC, 60 Hz single-phase (primary wiring selectable) |
Companion Transmitter | Collins 32S-3 |
Companion Amplifier | Collins 30L-1 Linear Amplifier |
Introduced | ~1964 (75S-3 base); 75S-3B and 75S-3C followed in subsequent years [10] |
Collector Status | Most common S-Line receiver. 75S-3B / 75S-3C most operationally desirable. Winged Emblem examples most valued by purists. |
Sub-Variant Guide: 75S-3 vs 75S-3B vs 75S-3C
Important: The 75S-3 series has three main sub-variants on the same basic chassis.
Sub-variant identification is important for operational assessment, manual selection, and collector
valuation. The front panel designation (“75S-3”, “75S-3B”, or “75S-3C”) and the number of filter
positions on the bandwidth selector are the primary identifiers.
| Sub-Variant | Approx. Production Era | Filter Positions | Key Differences | Collector Notes |
|---|---|---|---|---|
| 75S-3 (base) | ~1964 – ~1967 | 3 positions: 500 Hz, 2.1 kHz, 3.1 kHz | Original 75S-3 circuit. Three-position filter selector. Earlier tube complement. | Oldest sub-variant. Likely Winged Emblem. Three-filter operation is fully capable for SSB/CW. |
| 75S-3B | ~1967 – ~1972 | 4 positions: 500 Hz, 1.0 kHz, 2.1 kHz, 3.1 kHz | Added 1.0 kHz narrow SSB / data filter position. Revised AGC circuit. Improved strong-signal handling vs. base 75S-3. | Most operationally capable variant for contesting and DX operation. Found in both Winged and Small Round Emblem eras. |
| 75S-3C | ~1971 – ~1979 | 4 positions: 500 Hz, 1.0 kHz, 2.1 kHz, 3.1 kHz | Further refined AGC and product detector. Revised noise blanker interaction. Most refined 75S-3 variant. | Primarily Small Round and Large Round Emblem era. Most commonly found variant in late-production condition. |
Important Note on Serial Number Sequencing
⚠ Random Serial Number Assignment — Collins S-Line Policy
Per CCA historical research and a direct account from a former Collins employee,[9] Art Collins decreed that S-Line serial numbers were to be issued in random (non-sequential) order. For the 75S-3 series, which spans all three emblem eras and three sub-variants, the front-panel designation (75S-3 / 75S-3B / 75S-3C) and the emblem type together provide the most reliable dating guidance. Serial number ranges serve as supporting evidence.
Per CCA historical research and a direct account from a former Collins employee,[9] Art Collins decreed that S-Line serial numbers were to be issued in random (non-sequential) order. For the 75S-3 series, which spans all three emblem eras and three sub-variants, the front-panel designation (75S-3 / 75S-3B / 75S-3C) and the emblem type together provide the most reliable dating guidance. Serial number ranges serve as supporting evidence.
Collins Logo / Emblem Production Eras
Like the companion 32S-3 transmitter, the 75S-3 series spans all four Collins emblem types. The emblem is the most reliable quick-dating indicator.[3]
| Emblem Type | Production Period | Approx. S/N Range | Sub-Variant Expected | Physical Description |
|---|---|---|---|---|
| Winged Emblem | 1964 – Fall 1969 [3] | ~101 – ~12,000 (approx.) | 75S-3 (base) and early 75S-3B | Classic silver-and-blue winged Collins insignia. Most desirable to collectors. |
| Round Emblem Transition | Fall 1969 only [3] | ~11,000 – ~13,500 (overlap zone) | 75S-3B | Round “meatball” emblem plus two small grey screws flanking. Extremely rare — least common 75S-3 variant. |
| Small Round Emblem | Fall 1969 – ~1975 [3] | ~12,000 – ~25,000 (approx.) | 75S-3B and early 75S-3C | Circular Collins emblem (~18 mm diam.). No flanking screw holes. Post-Rockwell acquisition era. |
| Large Round Emblem | ~1974 – FY1976/1979 [3] | ~23,000 – ~35,000+ (approx.) | 75S-3C (primarily) | Round Collins emblem (~21 mm diam.). Slightly bolder typeface. Late Rockwell-Collins era. |
Serial Number Lookup Reference
Quick Era Identifier — Enter Your Serial Number
Documented Serial Number Data Points
| Serial Number | Sub-Variant | Emblem / Era | Notable Features | Source / Reference |
|---|---|---|---|---|
| ~1,xxx – 3,xxx range | 75S-3 (base) | Winged | Earliest 75S-3 production; c.1964–1966. Three-position filter selector standard. Original tube complement typically intact on unrestored examples. | CCA S-Line survey data [4] |
| ~5,xxx – 11,xxx range | 75S-3B | Winged | Mid Winged era; c.1967–1969. Four-position filter selector confirms 75S-3B. Most commonly encountered Winged Emblem 75S-3 variant in the collector market. | CCA survey / community documentation [4][7] |
| ~12,xxx – 13,xxx range | 75S-3B | Transition Zone | Emblem transition overlap; Fall 1969. Physical emblem inspection essential. Some units show grey screw transition emblem — extremely rare. | CCA survey [4] |
| ~16,xxx – 23,xxx range | 75S-3B / 75S-3C | Small Round | Post-transition production; c.1970–1974. Small Round Emblem (~18mm). Confirm front panel designation for sub-variant. | Collector community / eBay documented sales [7] |
| ~26,xxx+ range | 75S-3C | Large Round | Late Rockwell-Collins production; c.1975–1979. Large Round Emblem (~21mm). 75S-3C sub-variant. Final production era examples. | CCA survey / community [4] |
Manual Edition History
| Edition / Sub-Variant | Date | Notes |
|---|---|---|
| 75S-3 1st Edition | ~1964 | Original publication for base 75S-3. Three-filter configuration. Archived at CRA.[1] |
| 75S-3 subsequent editions | 1965–1968 | Service bulletin amendments incorporated. Available via CRA archive. |
| 75S-3B Instruction Book | ~1967–1969 | Separate manual for 75S-3B — covers four-position filter selector and revised AGC. Do not use 75S-3 base manual for 75S-3B service work.[2] |
| 75S-3C Instruction Book | ~1971–1975 | 75S-3C-specific manual. Covers revised AGC and product detector circuit changes. CRA archive recommended for all 75S-3C service work. |
Circuit Variations Across Sub-Variants
| Feature | 75S-3 (base) | 75S-3B | 75S-3C |
|---|---|---|---|
| Filter Bandwidth Selector | 3 positions | 4 positions (added 1.0 kHz) | 4 positions (same as 3B) |
| AGC Circuit | Standard hang AGC | Revised — improved strong-signal handling | Further refined — best strong-signal AGC of the series |
| Product Detector | Standard | Essentially same as base | Revised — improved audio quality |
| Noise Blanker Interface | Standard | Standard | Revised interaction with 136B-2 Noise Blanker accessory |
| Instruction Book | 75S-3 specific | 75S-3B specific | 75S-3C specific |
Physical Identification Guide
Step 1 — Front Panel Designation and Emblem
- Read the model designation on the front panel: “75S-3”, “75S-3B”, or “75S-3C” — this is definitive.
- Winged Emblem: 1964 – Fall 1969. Most valued by collectors.
- Round Emblem with grey flanking screws: Transition unit, Fall 1969 only. Extremely rare.[3]
- Small Round Emblem (~18 mm, dime-sized): Post-Fall 1969 to approximately 1974–1975.
- Large Round Emblem (~21 mm, nickel-sized): Mid-1970s through final production.
Step 2 — Filter Position Count
Count the bandwidth selector switch positions: three positions = 75S-3 base; four positions = 75S-3B or 75S-3C. This is the fastest sub-variant confirmation method short of reading the front panel label.
Step 3 — Serial Number Plate
Located on the rear panel. Plain integer — no alphabetic prefix or suffix. Cross-reference with range estimates and emblem type. Random S/N assignment means the serial number range alone is not definitive without emblem and front-panel sub-variant confirmation.[9]
Step 4 — Internal Component Date Codes
Electrolytic capacitors carry YY WW date codes. The latest original date code establishes the earliest possible ship date. Cross-referencing internal date codes with the emblem type and front-panel sub-variant designation is the most reliable dating method.
Step 5 — Instruction Book Edition
The 75S-3, 75S-3B, and 75S-3C have separate instruction books. Confirm that any accompanying manual matches the sub-variant designation on the front panel. Using the wrong sub-variant manual for service work risks incorrect alignment and schematic reference.[1]
Typical Restoration Considerations by Sub-Variant
| Component | All Sub-Variants — Recommended Action | Sub-Variant-Specific Notes |
|---|---|---|
| Electrolytic Capacitors | Reform or replace — first priority | All eras: 45–60+ year old electrolytics. Complete replacement recommended for stored units. |
| Power Supply Rectifiers | Replace with 1N4007 or equivalent | All sub-variants: replace selenium or early silicon rectifiers without exception. |
| Mechanical Filters | Test all fitted filters; confirm original types | 75S-3 base: verify three-position complement. 75S-3B / 75S-3C: verify all four filter positions are Collins Mechanical Filters of correct bandwidth for each position. Incorrect filter types (e.g., a 75S-3 3.1kHz filter in the 75S-3B 1.0kHz position) may have been substituted — confirm against manual part numbers. |
| AGC Alignment | Verify per applicable sub-variant manual | AGC circuits differ between base 75S-3, 75S-3B, and 75S-3C. Always use the correct sub-variant instruction book. Do not apply 75S-3 base AGC procedure to a 75S-3C. |
| Tube Complement | Test all tubes; prioritise RF, IF, and product detector stages | Original tube types per applicable instruction book. Replace weak examples with matched types. |
| PTO Stability | Evaluate drift only after 30+ minute warm-up | The permeability-tuned oscillator is precision Collins engineering. Do not adjust if within specification. If adjustment is required, follow the PTO alignment procedure in the applicable sub-variant manual exactly. |
| 136B-2 Noise Blanker Interface | Verify interface operation if 136B-2 is fitted | The 75S-3C has a revised noise blanker interface — confirm the 136B-2 (if fitted) is the correct version and that interface connections follow 75S-3C-specific wiring. 75S-3B and 75S-3C noise blanker wiring may differ. |
This guide consolidates publicly available CCA survey data, community restoration reports, and documented sale records. Serial number range estimates should be treated as approximations. Always verify sub-variant designation from the front panel before beginning service work — the three 75S-3 sub-variants are not interchangeable for manual or alignment purposes. Contributions and corrections welcome via vk6ada.com.au or r-390a.net.
References, Citations & Credits
- Collins Radio Company. 75S-3 Receiver Instruction Book. Cedar Rapids Division, Cedar Rapids, Iowa. Various editions ~1964–1969. Archived by the CRA: collinsradio.org — Technical Archives
- Collins Radio Company. 75S-3B and 75S-3C Receiver Instruction Books. Sub-variant-specific manuals. CRA archive: collinsradio.org
- Blocksome, Rod K0DAS. “The Collins S-Line Logo and Emblem Transition History.” CCA Historical Archives. 2013–2016. collinsradio.org — Historical Archives
- Blocksome, Rod K0DAS. Collins S-Line Receiver Production Surveys. CCA Technical Archives. Various years. collinsradio.org — Blocksome Surveys
- Collins Radio Association. Collins Radio Technical Archives. collinsradio.org
- WA3KEY Virtual Collins Radio Museum. Collins 75S-3 Reference Pages. wa3key.com. Accessed 2026.
- QRZ Forums — multiple threads documenting Collins 75S-3 / 75S-3B / 75S-3C serial numbers, sub-variant differences, and restoration notes. forums.qrz.com. Accessed 2026.
- Collins Collectors Association FAQ. Credits and biographical notes, including Dennis Day as prime engineer on the 75S-3 receiver series. Hosted by WA3KEY: wa3key.com/ccafaq.html. Accessed 2026.
- Anonymous (attributed to a former Collins employee; reported by Roger KB4THL). “[Collins] Winged versus Round Emblems.” QTH.net Collins Reflector, July 2005. qth.net — July 2005
- QST Magazine — Collins Radio advertisement, 75S-3 Receiver, ARRL, ~1964. QST archive: worldradiohistory.com
- Peace, Mike VK6ADA (Administrator). r-390a.net. r-390a.net.
- Peace, Mike VK6ADA. Collins S-Line Reference — vk6ada.com.au. vk6ada.com.au/collins-collection/. 2025–2026.