3T77

Manuals – Specifications – Links – Pictures

The Tektronix 3T77 is a sampling sweep plug-in for 560-series scopes. It was introduced in 1962, along with the 567 and 3S76, and superseded by the 3T77A in 1966.

Bob Webb and maybe Jim Geddes and possibly Cliff Moulton designed the a plug-in called "Type 77" (not to be confused with the identically named but totally different non-sampling sweep plug-in also called Type 77). The "Type 77" sampling sweep evolved into the 3T77. Cliff Moulton's circa-1961 paper on sampling credits Cal Hongel with contributions to the 567, 3S76, and 3T77.

Key Specifications

Sweep rate	0.2 ns/div to 10 μs/div (1–2–5); ×10 magnifier
Delay	Variable through 100 ns
Sweep Input	5 to 25 V/div into 28 to 100 kΩ

Links

Documents referencing 3T77

Document	Class	Title	Authors	Year	Links
Cliff moulton sensitive sampling plug-ins.pdf	Article	Sensitive Sampling Plug-ins and New Capabilities	Cliff Moulton	1961	Sampling • 561A • 3S76 • 3T77 • 567
Service Scope 31 Apr 1965.pdf	Article	Service Notes		1965	262 • 3T77 • 3S76

Patents that may apply to 3T77

Page	Title	Inventors	Filing date	Grant date	Links
Patent US 3317743A	Pulse generator circuit	John V Rogers	1962-06-11	1967-05-02	Sampling • 3T77 • 3T77A
Patent US 3359429A	Trigger generator circuit having synchronized astable input oscillator	Henry A Zimmerman	1964-03-23	1967-12-19	Sampling • 3T77 • 3T77A

Operation

The 3T77 can trigger on either the internal trigger pick-off from the vertical plug-in, or on an external trigger signal input. Triggering is faster and more sensitive with an external input.

The 3T77 can operate in any of four modes: external sweep, manual sweep, normal, or single sweep.

In external sweep mode, an external control voltage is applied to a BNC connector on the front panel of the 3T77. This voltage determines the X-position of the spot on the CRT and, correspondingly, the delay from the trigger event to the sampling point.

Manual mode is the same as external sweep mode, but the control voltage is generated internally based on the position of a potentiometer on the front panel of the 3T77.

In normal mode, an internal ramp generator produces the control voltage, repeatedly redrawing the trace on the CRT. In single sweep mode, the internal ramp generator is started by a button on the front panel, makes one horizontal trace, and then waits for the button to be pressed again.

Internals

While still tube-based, the 3T77 uses 2N976 transistors and 1N3129 tunnel diodes. It uses a 6688 tube in the staircase generator circuit, and an RCA 7586 nuvistor as a ramp-current generator. The 3T77 mixes "classic" chassis/ceramic strip construction with the trigger circuit built on a PCB.

Pictures

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  3T77 Front

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  3T77

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  3T77

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  3T77

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  3T77

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  3T77

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  3T77

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  3T77

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  3T77

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  3T77

Schematics

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  Trigger Schematic

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  Block Diagram

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  Connector and Power Supply

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  Horizontal Amp Schematic

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  Staircase Schematic

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  Fast Ramp Schematic

Components

Some Parts Used in the 3T77