1A5

The Tektronix Type 1A5 is a differential amplifier plug-in for 500-series scopes. It was designed by Bill DeVey after consultation with John Kobbe.

Manuals – Specifications – Links – Pictures

It has an Amphenol 165 series connector on the front panel for direct connection of the Type P6046 Active Differential Probe.

Type 1A5 was introduced in 1967, replacing Types W and Z, and lasted until the end of the 500-series scope line.

Key Specifications

Bandwidth	50 MHz down to 5 mV/div, 40 MHz at 1 mV/div
Deflection	1 mV/div to 20 V/div, 1−2−5
Common-mode rejection	20,000:1 from DC to 100 kHz, 10,000:1 up to 1 MHz, 200:1 at 20 MHz

Like most Tektronix differential plug-ins, the 1A5 has three modes: V_A−V_C, V_A−V_B, and V_C−V_B.

V_C is controlled by a ten-turn potentiometer and can vary from −5 V to +5 V (0.5 V on the 5 V/div to 20 V/div ranges).

Internals

The 1A5 is solid-state except for a pair of 7586 nuvistors used in the upper half of a cascode in the second amplifier stage.

The attenuator switching is mechanically complex. A gear mechanism drives the input attenuator switch (under the internal cover) selecting attenuators ×1000 (20 V/div to 5 V/div), ×100 (2 V/div to 500 mV/div), ×10 (200 mv/div to 50 mV/Div) or no attenuators (20 mV/Div to 1 mV/div).

Additionally, in the 500 mV/div and 50 mV/div positions, the operator can pull the V/Div knob outward when switching to one of the next two more sensitive ranges, in which case the higher attenuator (and higher input and comparison voltage range) remains in place.

Pictures

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Interior

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  Left side (attenuator cover removed)

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  Output board (left side) with HF Comp. daughterboard removed to show reed relays

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  Right side

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  Left side (attenuator cover in place)

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  Right side

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  Top

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  Top

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  Bottom

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  Rear

Switches detail

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Components