Dual-Concentric Potentiometer with Push-Pull Switch | 250K & 50K Linear Decks
Up for sale is a rare, vintage 1960s/1970s IRC Australia / CTS 45 Series dual-concentric potentiometer with a built-in mechanical Push-Pull switch array. This premium component assembly was carefully salvaged by me from a classic audio chassis. It remains in very nice physical condition with smooth rotation across both carbon tracks.
⚡ Multimeter Verified Specifications: This unit was individually sweep-tested on the bench to verify its linear taper curves. The top/outer deck (Nominal 250K) measures from a clean minimum of 34.7 Ohms up to 264K Ohms maximum, registering exactly 141.4K Ohms at the 50% halfway rotation mark. The bottom/inner deck (Nominal 50K) sweeps from 1.8 Ohms up to 50.7K Ohms maximum, tracking at 24.53K Ohms at the halfway midpoint.
🔊 Loudness & Switch Contact Layout: Features a built-in loudness tap on the bottom 50K potentiometer deck measuring at exactly 28K Ohms. The integrated push-pull mechanical switch setup includes both a **Normally Open (NO)** and a **Normally Closed (NC)** set of contacts, giving it excellent versatility for complex circuit routing or power control. Solder is present over the suffix of the rear factory stamps from its original installation, but all terminal lugs remain fully intact and structurally sound.
🔍 Vernier Caliper Measurements: Shaft parameters are measured directly. The center shaft diameter is 5mm, the outer shaft diameter is 6.2mm. The length of the shaft itself is 22mm, and the total length including the threaded mounting bushing is 32mm.
| Brand / Manufacturer | IRC Australia / CTS Components (45 Series Architecture) |
| Factory Tracking Code (Deck 1) | B3 250KOhm /A CZ034-111-1 CTS 45 |
| Factory Tracking Code (Deck 2) | 50KOhm /S3 CZ034-111-1 CTS 4... (Suffix obscured by solder) |
| Resistance Taper Curve | Linear Taper (Verified via 50% geometric rotation tests) |
| Deck 1 Range (250K Nom.) | 34.7 Ω Min | 141.4KΩ Mid (50%) | 264KΩ Max |
| Deck 2 Range (50K Nom.) | 1.8 Ω Min | 24.53KΩ Mid (50%) | 50.7KΩ Max |
| Special Audio Circuit Feature | Integrated Loudness Tap on 50KΩ Deck (Measures 28KΩ) |
| Switch Mechanical Action | Push-Pull Dual Function Mechanism |
| Switch Contact Routing | Dual-State Architecture: Normally Open (NO) & Normally Closed (NC) Contacts |
| Mains/DC Switch Rating | 2A 250V A.C. | 10A 12V D.C. |
| Shaft Sizing (Vernier Readings) | Center Shaft: 5mm Dia | Outer Shaft: 6.2mm Dia |
| Shaft Total Length | Shaft Only: 22mm | Including Threaded Bushing: 32mm total |
| Country of Origin | Australia |
| Condition Classification | Used / Clean Bench Salvage Pull |
This hyper-specific custom hybrid component configuration serves as a vital replacement part for: