Product Overview
Motorola 6-185A79 Carbon Composition Resistor File Card - 100k Ohm 1/2W 10% Tolerance, 10-Pack NOS
Condition
Unused NOS. Ten axial-lead resistors retained on the original Motorola card strip, brown bodies with color bands intact, all leads present and straight. Card tab markings legible: 6-185A79 and 100K10-1/2 confirming 100k Ohm, 10% tolerance, 1/2W. Reverse carries printed part number 54-84066A05. Card shows light surface scuffs and edge wear consistent with storage; no missing or damaged components observed. Sourced from an electronics distributor consolidating inventory.
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Product Overview
Motorola 6-185A79 is a 100k Ohm, 1/2 Watt carbon composition resistor packaged in the original Motorola file card format - 10 units per card. Resistance value and power rating are confirmed by the molded tab markings (100K10-1/2). Tolerance is 10%, consistent with standard carbon composition production of the era. Through-hole axial lead configuration. Brown-Black-Yellow-Silver band pattern visible on all units.
Key Features
- Resistance: 100k Ohm (100,000 Ohms)
- Power rating: 1/2 Watt (0.5W)
- Tolerance: 10%
- Type: Carbon composition, axial lead, through-hole
- Quantity: 10 resistors per file card
- Manufacturer part number: 6-185A79; alternate card reference: 54-84066A05
- Motorola Communications Division branding on card face
- All 10 units present; leads intact and straight
Applications
- Replacing failed or drifted carbon comp resistors in vintage tube radios and televisions to keep the circuit period-correct - desoldering the old part, dropping in a matched original-type replacement, and verifying value with a multimeter before powering back up
- Positioning at the grid of the input triode or other signal-path nodes in a boutique guitar amplifier build where carbon composition noise and thermal character are part of the intended tone
- Restoring vintage communications gear to factory-original spec - ham radio transceivers, early solid-state receivers, or military surplus equipment where substituting modern film resistors changes measured noise floor or circuit behavior in ways that matter to the restorer
- Maker and hobbyist projects calling for period-correct aesthetics on turret board or tag board builds, where the look and behavior of an original component are part of the finished piece
- Keeping a small bench stock of NOS carbon comp values on hand for the next vintage repair that walks through the door - a full card of 10 covers most single-job needs with spares
Frequently Asked Questions
Are these carbon composition or carbon film?
Carbon composition. The research confirms these are vintage carbon composition resistors - the type known for higher noise and the thermal character sought in vintage audio and tube amp work. Carbon film is a later, quieter type and is not what these are.
What do the color bands read and do they match the stated value?
Brown-Black-Yellow-Silver. That decodes to 100k Ohm with 10% tolerance, which matches the tab stamping (100K10-1/2) exactly.
Is the card complete - all 10 resistors present?
Yes. All 10 units are present on the card with leads intact. No missing or bent components observed.
Are carbon composition resistors suitable for modern precision circuits?
Not the right choice for low-noise or high-precision applications. Carbon composition resistors produce more electrical noise than metal film types and carry a wider tolerance (10% here). They are the right choice when vintage tonal character or period-correct construction is the goal - not when tight accuracy or quiet signal paths are required.
Some resistors just measure a value. These ones carry a sound - the particular warmth and grain that tube amp builders and vintage radio restorers go looking for by name. Whoever needs exactly this knows exactly why.
