Overview
The Motorola 6-5646 is a 390K ohm 1/2W carbon composition resistor rated for ±10% tolerance. This axial-leaded, through-hole component is a new old stock (NOS) example of Motorola’s legacy resistor technology, widely used in vintage tube amplifiers, radio receivers, and mid-century electronic equipment. Carbon composition resistors are valued for their warm sonic characteristics in audio circuits and their ability to operate reliably in high-temperature environments common to vintage gear.
Key Features
- Resistance: 390K ohm with ±10% tolerance
- Power Rating: 1/2W (0.5W)
- Construction: Carbon composition axial lead
- Manufacturer: Motorola — United States made
- Condition: New old stock (NOS), never installed
- Color Code: Orange-White-Yellow-Brown (standard EIA)
Technical Specifications
| Resistance Value | 390K ohm (390,000 Ω) |
| Tolerance | ±10% |
| Power Rating | 0.5W (1/2W) |
| Resistor Type | Carbon Composition, Axial Lead |
| Lead Diameter | 0.032″ (approx. 0.8mm) |
| Estimated Lead Length | 0.5″+ per side |
| Operating Temperature | -55°C to +85°C (typical for carbon composition) |
| Manufacturer | Motorola |
| Part Number | 6-5646 (or 5646) |
| Mounting Style | Through-Hole (Axial) |
Typical Applications
- Vintage Tube Amplifiers — Biasing networks, coupling circuits, and tone-shaping resistor ladders in guitar amps, bass amps, and hi-fi amplifiers.
- Retro Radio & Audio Equipment — RF, IF, and audio signal path resistors in AM/FM receivers and vintage audio gear.
- High-Voltage Electronic Circuits — Bleeder and voltage-divider applications where carbon composition reliability is preferred.
- Classic Test Equipment — Oscilloscopes, meters, and tube-based laboratory instruments.
- Component Matching & Restoration — Exact-value replacements for audio circuits requiring original Motorola specification parts for sonic and historical accuracy.
Compatibility & Replacements
Compatible With
- Any circuit requiring a 390K ohm ±10% 1/2W resistor
- Tube amplifier designs (guitar, bass, hi-fi, PA)
- Vintage radio and communication receivers
- High-voltage divider networks
- Audio signal path and coupling circuits
Replaces / Drop-In Replacement For
- Motorola 5646 carbon composition resistor (original factory numbering)
- Other 390K ohm 1/2W carbon composition resistors from the era (vintage equivalent)
- Note: Verify physical dimensions and lead spacing before substituting in tight PCB layouts.
Works With
- Hand-wired tube amp circuits and vintage PCB designs
- Point-to-point and turret-board assembly methods
- Breadboards and experimental circuits (vintage hobbyist builds)
- Any soldering iron or wave-solder process (standard through-hole)
