Sangamo
Sangamo CM08FD393G03 Silver Mica Capacitor, 0.039uF 500V 2%, MIL-C-5 Style CM08
- 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.
- 0:04
Specifications
| Specification | Value |
|---|---|
| Identification | |
| Part number | CM08FD393G03 |
| Manufacturer | Sangamo |
| Condition | New old stock, open stock |
| Date code | Not recorded |
| Package | Radial leaded dipped mica, both tinned leads from one edge, formed outward |
| Country of origin | Not recorded |
| Family | CM08 |
| Stock number | RJ834K6V |
| Electrical | |
| Capacitance | 0.039microfarad |
| Capacitance, marked code | 39,000 pF, coded 393 |
| Capacitance tolerance | 2% |
| Tolerance band at nominal | 38,220 to 39,780 pF |
| DC voltage rating | 500VDC |
| Characteristic | F, temperature coefficient 0 to +70 ppm per degree C |
| Capacitance drift limit | 0.05 percent plus 0.1 pF |
| Operating temperature range | -55 to +125 C, symbol O |
| Minimum insulation resistance at +25 C | 1,000 megohm microfarads, about 25,600 megohms at this value |
| Dielectric withstanding voltage | 200 percent of rated DC voltage, 1 to 5 seconds |
| Construction | |
| Dielectric | Silver electrode fired onto natural mica |
| Case | Dipped. Glossy deep reddish brown, rounded corners, slightly irregular edges where the coating pooled |
| Vibration grade | 3, MIL-STD-202 method 204 condition D, 10 to 2,000 Hz |
| Mechanical | |
| Lead configuration | Radial. Both tinned leads leave the same edge, one at each corner, formed outward into a splayed V. Measure the spread before committing a board to it |
| Body length at this rating | 1.340 to 1.450 in (34.0 to 36.8 mm) |
| Part number | |
| Governing specification | MIL-C-5/18F, styles CM04 through CM13, inactive for new design after 21 December 1970 |
| Commercial equivalent case | Cornell Dubilier CD42, catalogued as DM42 |
About this part
A Sangamo silver mica capacitor, 0.039 uF at 500 volts DC, plus or minus 2 percent. MIL-C-5 defines every field of CM08FD393G03: CM08 the case style, F the characteristic, D the 500 volt rating, 393 the 39,000 pF, G the 2 percent tolerance, then temperature symbol O and vibration grade 3.
Characteristic F is the tight one: temperature coefficient 0 to plus 70 ppm per degree C, drift within 0.05 percent plus 0.1 pF. That is the argument for mica: the crystal cleaves into sheets of even thickness, the silver is fired onto it rather than wound in as a foil, and the stack barely moves with heat, age or voltage.
So it was never a bypass part. A capacitor this steady goes where the value is part of the answer: oscillator tanks, crystal loading, filter and timing networks. The leads are radial, not axial: both leave one edge, one at each corner, formed outward into a splayed V.
Mica keeps well in a drawer, but has one real failure mode: silver ion migration. Under DC bias with moisture and heat, silver creeps across the mica face and builds a conductive path, so insulation resistance falls and the part shorts. Meter it before fitting.
This one is clean: no chips or cracks in the dip, no corrosion at the lead exits, bright leads. Sangamo Electric of Springfield, Illinois built watt hour meters from 1899 and mica capacitors through the second world war, until Schlumberger bought it in 1975.
Questions about this part
How do I read CM08FD393G03 field by field?
CM is a fixed mica dielectric capacitor under MIL-C-5, dipped case in this style. 08 is the case style. F is the characteristic. D is the 500 volt DC rating. 393 is the capacitance in picofarads with the last digit as the zero count, so 39,000 pF, which is 0.039 uF. G is the tolerance. The last two characters are the operating temperature range symbol and the vibration grade.
Is the ending 03 or O3?
It is the letter O followed by the digit 3. O is the temperature range symbol for minus 55 to plus 125 degrees C in MIL-C-5/18F, and 3 is the vibration grade. The letter and the zero are almost identical in the printing on these bodies, so distributors list the same part as G03 and GO3 and both refer to the same thing.
What exactly does the G guarantee?
Plus or minus 2 percent on capacitance. MIL-C-5/18F sets the symbols directly: D is plus or minus 0.5 pF, F is 1 percent, G is 2 percent and J is 5 percent. At 39,000 pF nominal that puts the part between 38,220 and 39,780 pF.
Why specify mica here instead of a ceramic?
Because of characteristic F. The temperature coefficient is bounded between 0 and plus 70 parts per million per degree C and the drift limit is 0.05 percent plus 0.1 pF. A class 2 ceramic of the same value moves by whole percent with temperature, voltage and age. If the value sets a frequency or a time constant, that difference is the entire reason for the part.
What is silver mica migration, and does it affect stored stock?
Silver from the fired electrode migrates across the mica surface under DC bias when moisture and heat are present, forming a conductive path. Insulation resistance falls and the part can eventually short. It needs bias, humidity and time, so an unused part stored dry is a poor candidate for it, but it is the failure to test for rather than assume against.
What should I measure before I fit it?
Capacitance on a bridge, expecting 38,220 to 39,780 pF. Dissipation factor, expecting a very low figure. Insulation resistance at room temperature, where the specification wants 1,000 megohm microfarads above 10,000 pF, roughly 25,600 megohms at 0.039 uF. Also inspect the coating for chips and cracks, since it is the moisture barrier.
Is there a current equivalent?
MIL-C-5 went inactive for new design on 21 December 1970 and points to MIL-PRF-39001/5. The commercial part of the same case and rating is the Cornell Dubilier CD42 family, catalogued as DM42, and the established reliability styles carry CMR numbering. Any of those is a substitute on paper, but none of them is this part.