Rectifier Diodes, Zener Diodes & SCRs: Polarity, Stud-Mount DO-4/DO-5 Identification and NOS Replacement Guide
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NOS rectifier diodes, zener diodes, and SCRs — including DO-5 and DO-4 stud-mount parts, 1N4004 rectifiers, 1N4742-type zeners, and C106 and C38 series SCRs — are in stock at American Industrial Parts Group, and new listings are added daily. This guide is part of our obsolete electronic components series; see the obsolete electronic components overview, our guide to vintage logic ICs and memory chips, and our 2N3055 transistor guide, then browse Vintage Diodes & Rectifiers and Vintage Thyristors & TRIACs.
Rectifier Diodes, Zener Diodes, and SCRs We Stock
| Part | Type | Key specification | Collection |
|---|---|---|---|
| 1N4004 | General-purpose rectifier diode | 1 A, 400 V repetitive reverse voltage, DO-41; the band marks the cathode | Vintage Diodes & Rectifiers |
| 1N4742 / ECG-142A | Zener diode | 12 V, 1 W, ±5%, DO-41 | Vintage Diodes & Rectifiers |
| NTE5994 | Silicon power rectifier, DO-5 stud mount | 600 V, 40 A, cathode to stud | Vintage Diodes & Rectifiers |
| ECG6045, SK7245 | Stud-mount rectifier, DO-5 | See product listings (the SK7245 is reverse polarity) | Vintage Diodes & Rectifiers |
| 1N1602 / ECG5181AK | 10 W stud-mount zener, DO-4 | 6.8 V, 10 W, DO-4 (DO-203AA); see listing for stud polarity | Vintage Diodes & Rectifiers |
| MB3510 | Single-phase bridge rectifier | See product listing | Vintage Diodes & Rectifiers |
| C106D | Sensitive-gate SCR | 4 A RMS, 400 V, TO-225AA | Vintage Thyristors & TRIACs |
| C38M | Stud-mount SCR | 600 V, 35 A, TO-48 | Vintage Thyristors & TRIACs |
Rectifier, Zener, and SCR Basics: Anode, Cathode, and Stud Polarity
- SCR (silicon controlled rectifier): a four-layer PNPN thyristor with three terminals: gate, anode, and cathode.
- Axial diodes: on parts like the 1N4004, the band marks the cathode.
- Stud packages: DO-4 is the DO-203AA outline and DO-5 is the DO-203AB outline. Typical thread sizes are 10-32 UNF for DO-4 and 1/4"-28 UNF for DO-5. TO-48 is the stud package used for the C38M.
- Stud polarity on rectifiers: standard polarity has the stud as the cathode, and reverse polarity (an "R" suffix, or a separate number) has the stud as the anode. The NTE5994 is cathode to stud, and the NTE5995 is the anode-to-stud version.
- Stud polarity on zeners: 10 W DO-4 stud zeners are made with the stud as either the anode or the cathode, so check the polarity stated on each listing.
- NTE, ECG, and SK numbers: replacement-brand and house numbers that map to original manufacturer part numbers. NTE Electronics closed in 2024, so matching by original number and ratings matters more than ever.
Common Diode and SCR Problems and What to Do
- Rectifier shorts or overheats: find out why it failed before installing a new one, and never go below the original voltage and current ratings.
- Zener voltage is out of range: match both the zener voltage and the power rating. For example, the 1N4742A is a 12 V, 1 W part.
- Can't tell the stud polarity: standard stud parts have a cathode stud and reverse ("R") parts have an anode stud, but confirm against your circuit and the listing.
- Original part is obsolete: onsemi's C106D is listed as obsolete and no longer manufactured. NOS stock lets you buy the original part.
- Need matched parts for a full repair: many items are available in lots of 10.
Compatibility Notes Before You Order
- Stud polarity: a cathode-stud part and an anode-stud part are not interchangeable in the same circuit.
- Package and thread: DO-4 and DO-5 are different sizes. Confirm the stud thread and mounting hole for your heat sink or chassis.
- Gate sensitivity on SCRs: the C106D is a sensitive-gate SCR with a maximum gate trigger current of 200 µA, while the C38M lists a maximum gate trigger current of 150 mA. Do not swap one for the other without checking your gate drive.
- Heat sinking: stud-mount parts are designed to be fastened to a heat sink or chassis. Mounting hardware is not included unless listed.
- Condition: each listing states whether the part is NOS, new, or used.
Rectifier, Zener, and SCR FAQ
What is an SCR?
An SCR, or silicon controlled rectifier, is a four-layer PNPN thyristor with three terminals: gate, anode, and cathode.
How do I tell stud diode polarity?
Standard-polarity stud diodes have the stud as the cathode, and reverse-polarity ("R") versions have the stud as the anode. Always check the polarity stated on the listing and match your circuit.
What is the difference between DO-4 and DO-5?
They are different stud-mount package sizes: DO-4 is the DO-203AA outline and DO-5 is the DO-203AB outline. Typical threads are 10-32 UNF for DO-4 and 1/4"-28 UNF for DO-5.
How often is new inventory added?
New vintage diodes, rectifiers, and thyristors are added to the site daily. Check the collections below for the latest listings.
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