Я4С-91

The Я4С-91 is a dual timebase plug-in for Soviet 7000-series clones. It is roughly analogous to the Tek 7B52. It features two 3И306К tunnel diodes in the timebase A trigger circuit.

Significant differences to the 7B52 include:

• slowest sweep speed 50 ms/div
• no ×10 magnifier, direct access to 5 ns/div speed
• timebase B always runs after timebase A and has no separate trigger
• delay time is set by a single-turn pot with a reduction drive, and it is not calibrated
• only timebase B has variable time/div

The external trigger connector is a СР50-73 type. The trigger level control has no separate slope switch. Trigger levels left of centre are on the falling edge, and those right of centre are on the rising edge. This is similar to the way the trigger level control works on the 7B52. The plugin contains a number of integrated circuits of type 130ЛА3, which is a TTL quad 2-input NAND gate in a surface-mount package, like a 7400.

The main interconnect board, which also holds the timing capacitors, is made of a rather weak Paxolin- or FR2-like phenolic paper material rather than fibreglass, and the tracks appear to be silver plated. The example in the photos suffered a crack at one corner which caused a malfunction (triggering only after pressing the single-sweep-reset button, and trace offset to the left).

The example in the photos is labelled in German. A version labelled in Russian also exists.

Key Specifications

Time/div	50 ms to 5 ns
Trigger modes	norm, auto, single sweep
Trigger sources	internal, external, external/10, line

Pictures

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  Front

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  Three-quarter view

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  Left side internal

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  Left side detail

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  Timebase A PCB

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  Tunnel diode in Timebase A trigger

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  Right side internal

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  Right side detail

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  Timebase B PCB

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  Output amplifier PCB

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  Closeup of PCB construction

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  Factory-added tape to insulate capacitors from side panel

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  Cam-operated microswitch to select variable time/div

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  Interconnect board (Timebase B and output amplifier removed)

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