El-Menco
El-Menco CM05FD271J03 Silver Mica Capacitor, 270 pF 500 V 5 Percent, MIL-C-5 Style CM05
- 2 photos
Never used. The original pack has been opened, or the quantity was split off a full reel or tube. Leads are original and unclipped.
New old stock, open stock 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.
- 0:14
Specifications
| Specification | Value |
|---|---|
| Identification | |
| Part number | CM05FD271J03 |
| Manufacturer | El-Menco |
| Condition | New old stock, open stock |
| Date code | Not recorded |
| Package | Moulded rectangular mica case, radial leads |
| Country of origin | Not recorded |
| Family | CM05 |
| Stock number | S9ZM9PKT |
| Overview | |
| Type | Silver mica, moulded case |
| Military part number | CM05FD271J03 |
| Specification | MIL-C-5, fixed mica dielectric capacitors |
| Case style | CM05 |
| Electrical | |
| Capacitance | 270 pF, from the 271 code and printed in full on the second face |
| Tolerance | Plus or minus 5 percent, from the J code and printed in full |
| DC voltage rating | 500 V, from the D code and printed in full |
| Characteristic | F, which fixes the temperature coefficient and the permitted drift |
| Polarity | None. Mica capacitors are not polarised |
| Markings as read | |
| Marking, face 1 | 270 plus or minus 5 percent, 500V, EM |
| Marking, face 2 | CM05FD over 271J03 |
| Provenance | |
| Manufacturer | El-Menco, from the EM mark on the value face |
| Quantity offered | One piece |
| Condition | New old stock, unused, case unchipped and leads unsoldered |
| Basis of identification | Two independent printed faces that agree with each other |
| Physical | |
| Lead style | Radial, both leads from the same edge |
| Body | Moulded rectangular case, deep reddish brown, rounded corners |
About this part
An El-Menco silver mica capacitor carrying a full military part number, CM05FD271J03, with the value printed in plain language on the other face: 270 plus or minus 5 percent, 500V, EM. New old stock, unused.
The pleasure of a part like this is that nothing has to be guessed. The military numbering system spells out every parameter in sequence, so the two faces of this capacitor independently confirm each other. CM05 is the case size under MIL-C-5. The F is the characteristic, which sets the temperature coefficient and the maximum capacitance drift. The D is the voltage code and means 500 volts DC, exactly what is printed on the other side. 271 is the capacitance in the three digit convention, 27 followed by one zero, so 270 pF. The J is the tolerance letter and means plus or minus 5 percent. The final field is the temperature range symbol and vibration grade.
Worth knowing: the character that looks like a zero in that last field is the letter O, the temperature range symbol. Distributors list these part numbers both ways, so if you are searching for a replacement it is worth trying both spellings.
El-Menco was the trade name of the Electro Motive Manufacturing Company of Willimantic, Connecticut, and they were one of the two or three names that mattered in American precision mica through the valve era. Their capacitors turn up throughout period radio, television, test gear and military equipment.
Mica is the most stable dielectric in common use and it does not age on a shelf.
Questions about this part
What does CM05FD271J03 decode to, field by field?
CM05 is the case size under MIL-C-5. F is the characteristic, setting the temperature coefficient and the allowable capacitance drift. D is the voltage code and means 500 volts DC. 271 is the capacitance, 27 followed by one zero in picofarads, so 270 pF. J is the tolerance and means plus or minus 5 percent. The last field is the temperature range symbol and the vibration grade. Every one of those is confirmed by the plain language marking on the opposite face.
Is the last character a zero or a letter O?
It is the letter O, the temperature range symbol, and it trips people up constantly. Distributors catalogue these part numbers both ways, with a zero and with an O, so if you are hunting a replacement and a search comes up empty, try the other spelling before concluding the part does not exist.
Why would I want a mica capacitor rather than a modern ceramic?
Stability. Mica is a natural crystal that is dimensionally and thermally stable in a way no class 2 ceramic approaches, so the value holds across temperature, across DC bias and across decades. In a tuned circuit, an oscillator or a timing network that is the difference between a radio that stays on frequency and one that drifts. For bypass and decoupling, a ceramic is cheaper and just as good.
Who were El-Menco?
The trade name of the Electro Motive Manufacturing Company of Willimantic, Connecticut. They were one of the small number of American firms that mattered in precision mica through the valve era, supplying radio, television, instrumentation and military equipment, and their moulded micas are a common sight in any American set of the period.
Does a mica capacitor deteriorate in storage?
Practically not at all, which is what makes them worth buying old. There is no liquid to dry, no oxide layer to reform and no seal to perish. The dielectric is a mineral. The recognised long term failure mode in silver mica is silver migration under sustained voltage and humidity, and it is a service phenomenon rather than a shelf one. A capacitor that has never been powered has not started down that road.
What does the F characteristic actually restrict?
It is a bundle of guarantees rather than a single number. The characteristic letter fixes the maximum temperature coefficient, the permitted capacitance drift over a temperature cycle, and the minimum insulation resistance. F is a mid range characteristic in this family, tighter than the loosest grades and looser than the very best. If a circuit depends on the value holding to a specific figure, the characteristic is the field to read, not just the tolerance.
What condition is this one in?
New old stock, open stock, never fitted. The moulded case has no chips or cracks, both printed faces are fully legible, and the leads are unsoldered with no kinks from a previous installation. The photographs show the actual capacitor you would receive.