GE 2N491 Vintage Silicon Unijunction Transistor TO-5 Gold Leads NOS

Vintage GE 2N491 Unijunction Transistor with Gold-Plated Leads

Condition

New old stock (NOS). Unused vintage component. Leads are straight and clean with intact gold plating. Markings legible: embossed GE monogram on top of can; 2N491 stamped on can body.

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Product Overview

Silicon unijunction transistor (UJT) architecture with an N-type silicon bar in a hermetically sealed TO-5 metal can. Designed for timing circuits, pulse generators, relaxation oscillators, and SCR trigger stages, this vintage GE component features three gold-plated wire leads for corrosion resistance in analog restorations and bench repairs.

Key Features

• Silicon unijunction transistor (UJT) architecture
• Intrinsic standoff ratio (η) of 0.56 to 0.68
• Interbase resistance (rBB) of 4.7 kΩ to 6.8 kΩ
• Maximum continuous power dissipation of 450 mW
• Welded hermetic TO-5 metal can housing
• Three gold-plated wire leads (Emitter, Base 1, Base 2)

Applications

• Servicing vintage industrial timers, pulse generators, and relaxation oscillator circuits.
• Restoring analog test instruments and legacy thyristor/SCR triggering controls.
• Breadboarding discrete timing and synthesizer trigger experiments on the maker bench.

Frequently Asked Questions

What is the pinout configuration for the TO-5 unijunction transistor?

The three leads correspond to Base 1 (B1), Emitter (E), and Base 2 (B2). In the standard TO-5 unijunction layout, the lead adjacent to the case tab is Base 1, the center offset lead is the Emitter, and the remaining lead is Base 2.

What modern solid-state part directly replaces the vintage 2N491?

The NTE6400A is the industry standard cross-reference replacement for the 2N491 unijunction transistor in relaxation oscillators and SCR trigger circuits.

Before integrated 555 timers ran the show, humble silicon unijunction cans like this shaped the pulses and kept analog time. Solder it in and bring that classic oscillator circuit back to life.