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Tektronix 3S76
Dual Channel Sampling plug-in
Tektronix 3S76 Front

Compatible with 560-series scopes

Produced from 1962 to (?)

(All manuals in PDF format unless noted otherwise)
Manuals – Specifications – Links – Pictures

The Tektronix 3S76 is a dual-trace sampling plug-in for 560-series scopes. The inputs have 50 Ω impedance and use GR-874 connectors. Rise time is rated at less than 0.4 ns.

The initial design work on the 3S76 was done by Cliff Moulton. It was called the Type 76, later renamed 3S76 before going into production. A decision was made to demonstrate the 76/3S76 at the 1961 IRE show. This created a panic because the plug-in was not complete. The 76 project landed in the TV group. Ron Olson and Charlie Rhodes were designing it and Walt Lowy was a technician. Phil Crosby worked on it for a week during spring break from Portland State (college then, not university). Phil Crosby designed the channel switching circuitry.

Key Specifications

Rise time < 400 ps
Bandwidth 875 MHz
Input impedance 50 Ω
Triggering Internal trigger take-off, 55 ns delay line

Early 3S76 units are marked RT. ≈ 0.4 nSEC on the front panel. Later 3S76 units are marked RT. ≤ 0.4 nSEC on the front panel.


The 3S76 contains 10 Germanium transistors in TO-7 cases, which are prone to failure due to internal growth of tin whiskers. See the Repairs tab about replacing these with 2N3906s.

Each input has a trigger takeoff transformer and a 55 ns coaxial delay line. The trigger source channel is selectable.

Each delay line terminates at that channel's sampling bridge, which is a four-diode design using beam-lead GaAs diodes.

A 7586 nuvistor buffers the output of each sampling bridge. The sampling pulse, common to both channels, is generated by a 152-115 snap-off diode and a 3 cm twisted-pair clipping line.



Some Parts Used in the 3S76

Part Part Number(s) Class Description Used in
152-115 152-115 152-0115-00 Discrete component step recovery diode 3S3 3S76
2N1516 151-015 Discrete component Germanium PNP transistor 3S76
2N2207 151-063 151-0063-00 Discrete component germanium PNP transistor 3B1 3B3 3S76 321A 547
6922 154-0195-00 Vacuum Tube (Dual Triode) dual triode 3S76 4S2
6CW4 154-0323-00 Vacuum Tube (Triode) Nuvistor triode 1A7 3A8 3B2 3S76 6R1 565 S-311
6DJ8 154-0187-00 154-0305-00 Vacuum Tube (Dual Triode) dual triode 132 161 310A 316 317 502 502A 503 504 506 515 516 519 526 529 RM529 533 535 536 543 544 545 545A 545B 546 547 549 555 556 561A 561S 564 565 567 581 581A 585 585A 661 1A4 1S1 60 2A60 63 2A63 67 2B67 3A1 3A1S 3A2 3A3 3A6 3A7 72 3A72 75 3A75 4S2 51 3B1 3B1S 3B2 3B3 3B4 3M1 3S76 3T77 3T77A 9A1 9A2 1121 80 81 82 86 B O W Z Telequipment D56 Telequipment S32A Telequipment D52 S-311 Telequipment TD51 Telequipment S52 Telequipment S51 Telequipment Type A TU-4
7308 154-0371-00 Vacuum Tube (Dual Triode) dual triode 3S76 3S3 4S1 4S2A 4S3 S-311
7586 154-0306-00 Vacuum Tube (Triode) Nuvistor triode M 1A1 1A2 1A5 10A2 10A2A 11B1 11B2A 321 321A 3A1 3A1S 3A3 3A5 3A6 3A7 3A8 3A74 3S76 3T77 3T77A 3B5 4S1 4S2 6R1 6R1A 9A1 9A2 82 86 S-311
RT5204 151-0058-00 Discrete component Silicon NPN transistor 565 RM565 Z 2A61 3B1 3B3 3S76 3T77
ZZ1000 154-370 154-0370-00 Gas Discharge Tube (Voltage regulator) 81 V voltage reference 129 3B1 3B1S 3B2 3B3 3S76 422 S-311