KOA Speer Electronics
KOA Speer CF1/4 2.7 Ohm 1/4 Watt Carbon Film Resistor, Axial
- 7 photos
Never used and never opened. Still in the factory tube, tray, reel or bag it shipped in, with the original date code intact.
New old stock, sealed on the grading scaleSend the quantity you need. You get a quote back with shipping before anything is charged.
Video
Filmed on the bench. Sound is stripped from product clips.
- 0:22
The clip opens on the tape stack, showing how tightly the carrier is wound.
Specifications
| Specification | Value |
|---|---|
| Identification | |
| Part number | CF1/4 |
| Manufacturer | KOA Speer Electronics |
| Condition | New old stock, sealed |
| Date code | Not recorded |
| Package | Axial leaded |
| Country of origin | Not recorded |
| Family | Not recorded |
| Stock number | 9V4JS2MA |
| Electrical | |
| Resistance | 2.7ohm |
| Power rating at 70 C | 0.25W |
| Maximum working voltage | 300V |
| Temperature coefficient, series range | +350 to -1300ppm/C |
| Operating temperature range | -55 to +155C |
| Endurance at 70 C, 1000 hours | 3 percent maximum change |
| Construction | |
| Composition | Carbon film on high grade ceramic core, helically trimmed |
| Coating | Insulating coating. Flameproof version available as CFP1/4 |
| Mechanical | |
| Body length | 0.240 in +0.028 / -0.02 (6.1 mm +0.7 / -0.5) |
| Body diameter | 0.092 +/- 0.012 in (2.3 +/- 0.3 mm) |
| Lead diameter, nominal | 0.024 in (0.6 mm) |
| Ordering | |
| Tolerance options in this series | G is 2 percent, J is 5 percent |
| This lot | |
| Tolerance | 5 percent, code J, read from the reel label |
| Lot quantity on the reel label | 5000 |
| Full ordering number | CF1/42R7JT52 |
| Lot number | 56010818 |
| Lot date | 02-10-00 |
| Country of manufacture | Taiwan |
About this part
CF1/4 is KOA Speer's quarter watt carbon film axial resistor, made by depositing a carbon film onto a high grade ceramic rod, cutting a helical trimming line to set the value, fitting end caps and leads, then coating the body. At 2.7 ohms this is a low value part, the kind used for emitter degeneration, small series damping, inrush limiting and rough current sensing.
Rated power is 0.25 W at 70 degrees C with derating above that, and the operating range is -55 to +155 degrees C. The body is roughly 6.1 mm long by 2.3 mm diameter on 0.6 mm leads, the standard size for automatic insertion. KOA notes that the CF family holds up better under pulse loading than a chip resistor of the same rating, which is part of why it stayed in switching supplies and audio gear long after surface mount took over elsewhere. A flameproof version was sold as CFP and a short body version as CFS.
When buying old stock, confirm the tolerance letter on the packaging, G for 2 percent or J for 5 percent, because both were catalogued. Low value carbon film parts also sit in a wider temperature coefficient band than mid range values, so check the applicable band before using them where the coefficient matters.
Questions about this part
What does CF1/4 mean?
CF is the carbon film leaded resistor family and 1/4 is the 0.25 W power rating. A complete KOA ordering number adds a termination material code, a taping and forming code, the resistance code and the tolerance code.
What is the voltage rating?
Maximum working voltage for the CF1/4 is 300 V. At 2.7 ohms the power rating is the binding limit long before voltage is, since 0.25 W across 2.7 ohms is only about 0.82 V.
Is 2.7 ohms a standard value in this series?
Yes. 2.7 is an E24 value and the CF series resistance range extends down into single digit ohms.
How much current can a 2.7 ohm CF1/4 carry?
Rated dissipation is 0.25 W at 70 degrees C. Into 2.7 ohms that works out to roughly 300 mA continuous at 25 degrees C ambient, and less as ambient rises.
Is this a flameproof part?
Not unless the marking reads CFP. The flameproof coating and testing apply to the CFP and CFPS variants. The plain CF1/4 does not carry that qualification.
What tolerance is the lot?
The CF series is offered at plus or minus 2 percent, code G, and plus or minus 5 percent, code J. Read the letter from the packaging rather than assuming.
Can carbon film be used where precision matters?
No. Carbon film drifts with temperature far more than metal film, and the coefficient is worse at low resistance values. Use a metal film part instead.