Product Overview
Mallory CG42U100A1 Can Capacitor, 400 MFD at 100 WVDC, Unused Old Stock
Condition
New, unused old stock out of original P. R. Mallory packaging. Under the clear Mylart sleeve the aluminum can is bright and the factory printing is still crisp: MALLORY, MADE IN USA, CG42U100A1, 400 MFD 100 VDC, POS RED, MAX SURGE 135 VDC. Both screw terminals are clean and straight, with no solder, no wire nicks, and no scoring from a wrench. The black terminal end disc carries the red positive marking beside one turret and the round safety vent beside the other. The cartons show their age, with creased corners, scuffed edges, and rubbing across the printed panels; the capacitors inside do not. These test out.
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Product Overview
The CG42U100A1 is a high capacity aluminum electrolytic capacitor from P. R. Mallory and Co. Inc. of Indianapolis, Indiana, rated 400 MFD (400 uF) at 100 WVDC with a 135 VDC maximum surge printed right on the can. It is an upright two-terminal can: screw-slotted turret terminals rise from a black insulating end disc, positive identified in red per the POS RED marking on the body, with Mallory's safety vent set into that same end. A clear Mylart insulating sleeve wraps the can and is intact on the unit photographed. Against the ruler the body measures approximately 2-3/8 inches long by about 1-1/2 inches in diameter, roughly 2-3/4 inches overall with the terminals standing proud. The can is printed 100 VDC and the carton end label 100 WVDC; both describe the same 100 volt DC working rating.
Key Features
- Part number: CG42U100A1, printed on the can and on the carton end label
- Capacitance: 400 MFD (400 uF)
- Working voltage: 100 WVDC
- Maximum surge: 135 VDC, printed on the can
- Construction: aluminum electrolytic can with Mylart insulating sleeve
- Terminals: two screw-slotted turret terminals on an insulating end disc
- Polarity: positive marked in red, per the POS RED marking on the body
- Safety vent: Mallory vent disc set into the terminal end
- Temperature range: -20 C to +85 C, per the Mallory catalog entry for this family
- Tolerance: -10, +75 percent, per the Mallory catalog for 0-150 WVDC units
- Size: approximately 2-3/8 in long by 1-1/2 in diameter against the ruler, about 2-3/4 in overall with terminals
- Origin: made in USA, P. R. Mallory and Co. Inc., Indianapolis, Indiana
Applications
- Restorer rebuilding a low voltage supply filter section who wants a period-correct American can instead of a modern radial
- Bench technician who needs bulk reservoir capacitance on a DC rail sitting comfortably under the 100 volt working figure
- Collector or museum volunteer keeping a chassis original down to the brand printed on the capacitor
- Hobbyist building a discrete supply who wants screw terminals to land ring lugs on, not snap-in pins
Frequently Asked Questions
How can a capacitor this old be listed as unused?
Because the wear is on the cardboard, not the part. The cans are bright under their sleeves, the factory ink is sharp enough to read across a bench, and the screw terminals carry no solder, no wire nicks, and no wrench marks. What is battered here is the carton: creased corners, scuffed edges, rubbed printing. The capacitor is the thing that stayed still.
Should I reform it before putting it into service?
Treat it like any aluminum electrolytic that has sat unpowered for decades. Bring the voltage up slowly through a current limiting resistor or a variable supply and let the leakage settle before you put it on a live rail. These check out here, but a slow reform costs you nothing and is the difference between a quiet capacitor and a loud one.
Which terminal is positive?
The can is printed POS RED, and the terminal end disc carries a red marking next to one of the two screw turrets. That turret is positive; the other is negative. Aluminum electrolytics are polarized, so check the marking on the piece in your hand before you wire it. The close-up photo of the terminal end shows exactly where to look.
The can says 100 VDC and the box says 100 WVDC. Is that the same rating?
Same rating. WVDC is working volts DC, the continuous voltage the capacitor is built to sit at. The 135 VDC printed under it on the can is the maximum surge, a short-term limit rather than an operating point. Design against the 100 volt number.
I only need two of these. Do I have to buy a whole lot?
No. Count out what the chassis actually needs and buy exactly that. Vintage cans usually surface as estate lots and auction boxes of mixed values, where you pay for forty unknowns to get the three you can use. This is one known value, photographed from every side and priced by the piece, with more of the same run on the shelf if the recap turns up needing another. Shipping is $8 flat rate and free once your order passes $28, and orders leave our Idaho warehouse the same or next business day.
P. R. Mallory boxed these in an Indianapolis that still wrote its address with a postal zone instead of a ZIP code, and the ink on the can is as sharp as the day it left the line. Six decades of sitting still, and the first job of its life is the one waiting on your bench.
