Parts · Diodes
OA90
Ge Signal Diode TH.10 circuits use this part. Listed as: Semiconductors; Germanium diode.
Datasheet · archived copy from BKC International; the part is discontinued and the maker no longer publishes it
Substitutes same kind
Diodes of the same kind; for clipping, the forward drop is what you hear. The figures are read off each part's datasheet (this one's from page 1), typical where the sheet gives a typical value, otherwise the maximum. Closest first; the last column says what differs. A different part can change the sound, and a circuit may lean on one particular figure, so read the build document's notes before you swap.
This part
| Part | Vf | If max | Vr | trr | Cj | Package | Boards |
|---|---|---|---|---|---|---|---|
| OA90 | 1 V @ 10 mA | 30 V | 10 |
Gold-bonded germanium; Vf is only a 1 V maximum at 10 mA, so the low knee is not specified.
Alternatives
| Part | Vf | If max | Vr | trr | Cj | Package | Boards | Differs |
|---|---|---|---|---|---|---|---|---|
| 1N34A | 1 V @ 5 mA | 0.05 A | 65 V | DO-7 | 332 | Vf is only a 1 V maximum at 5 mA, so the low knee that makes it a soft clipper is not specified; leakage is high (up to 500 µA at 50 V). | ||
| AA112 | 0.95 V @ 10 mA | 20 V | 3 | 20 V reverse. Gold-bonded germanium; Vf is only a 0.95 V maximum at 10 mA, so the low knee is not specified. | ||||
| 0A9 | 0.16 V @ 0.1 mA | 0.035 A | 25 V | 1 | OA9 gold-bonded germanium with a very low 0.32 V drop at 10 mA; single-ended glass body. | |||
| OA47 | 0.17 V @ 0.1 mA | 0.05 A | 25 V | 1 | Gold-bonded germanium with a low 0.40 V drop at 10 mA; a miniature OA7. | |||
| 1N270 | 1 V @ 200 mA | 0.04 A | 100 V | 0.8 pF | DO-7 | 64 | Vf is given only as a 1 V maximum at 200 mA, so the sheet says nothing about the clipping knee. | |
| 1N100 | 1 V @ 40 mA | 0.07 A | 100 V | DO-7 | 1 | Gold-bonded germanium; Vf is only a 1 V maximum at 40 mA, so the low knee is not specified. | ||
| OA91 | 0.18 V @ 0.1 mA | 0.05 A | 115 V | DO-7 | 8 | Point-contact germanium, typically 0.18 V at 0.1 mA (spread 0.1 to 0.25 V). | ||
| OA95 | 0.18 V @ 0.1 mA | 0.05 A | 115 V | DO-7 | 1 | Point-contact germanium, typically 0.18 V at 0.1 mA, slightly lower drop at 10 mA than the OA91. | ||
| AA119 | 1.5 V @ 10 mA | 45 V | 3 | higher forward drop. Gold-bonded germanium; Vf is only a 1.5 V maximum at 10 mA, so the low knee is not specified. |
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