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The Tektronix Type 3B4 is a timebase plug-in for 560-series scopes, introduced in 1964.

It was intended primarily for use with the 561A, but works fine in other 560-series scopes. The 3B4 is unusual in having an explicit "FREE RUN" mode.

In the triggered modes, the tunnel diode-based triggering is rated to work to 20 MHz. The vertical bandwidth of typical 560-series (non-sampling) scopes is about 10 MHz, so 20 MHz is adequate.

Triggering is done with a TD3A 4.7 mA tunnel diode. The trigger input is amplified and buffered by a 6DJ8-based differential amplifier driving a common-emitter 2N964 germanium PNP transistor whose collector current switches the tunnel diode.

The 283 Real Time adapter enables real-time sweeps with a 3B4.

Key Specifications

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Some Parts used in the 3B4

Page Class Description Used in
6DJ8 Vacuum Tube (Double Triode) dual triode 132 502 502A 503 504 515 516 519 533 535 543 544 545 545A 545B 546 547 549 555 556 565 581 581A 585 585A 661 2A60 2A63 3A8 1121 1A4 67 81 82 86 3B1 3B4 B O W Z Telequipment S32A Telequipment D52 Telequipment S52 Telequipment S51 Telequipment Type A
7119 Vacuum Tube (Dual Triode) dual triode 067-0532-00 191 3A3 3B4 3B5 516 545B 549 661