1A7A

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The Tektronix 1A7A, nominally designed by Thor Hallen and introduced in 1968, is a redesign of the 1A7 high-sensitivity differential amplifier plug-in for 500-series scopes. The 1A7 and 1A7A have essentially the same features including 10 μV/Div deflection factor when either AC or DC-coupled, high frequency and low frequency bandwidth limit filters, DC Offset, high common mode rejection ratio and large common mode dynamic range.

The 1A7A doubled the 1A7's bandwidth (to 1 MHz) and has a JFET input stage that greatly reduced input drift.

The 1A7A's differential amplifier design was re-used with some modifications in the 3A9, 3A10, 7A22, 5A22N and 5030/5031 scopes. The AM502 and 26A2 use BJTs instead of JFETs for the differential offset current sources.

Type 1A7A remained available until the end of the 500-series line.

John Addis says:

The 1A7A (designed by Thor Hallen) and the 7A22 (designed solely by Val Garuts) used essentially the same circuit. The brilliant input circuit was the work of Val Garuts. The 1A7A came out first. Thor had worked for at Tektronix for Val Garuts less than a year when the 1A7A was introduced. Thor later became famous for designing not just the 7904 (500 MHz mainframe) but also its 7A19 plugin. Thor died in 2002.

Key Specifications

Deflection	10 μV/Div to 10 V/Div in 1–2–5 sequence
Input impedance	1 MΩ // 47 pF (either input)
Bandwidth	1 MHz, LF limit switchable DC, 0.1 Hz to 10 kHz in ×10 steps, HF limit switchable 100 Hz to 1 MHz in ×3/×10 steps, AC coupling 1.6 Hz
Signal ranges

Range	Differential signal	DC Offset	Common mode
10 μV/Div to 10 mV/Div	±0.4 V	±0.4 V	±10 V
20 mV/Div to 0.1 V/Div	±4 V	±4 V	±100 V
0.2 V/Div to 1 V/Div	±40 V	±40 V	±500 V
2 V/Div to 10 V/Div	±400 V	±400 V	±500 V

Pictures

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Components

Some Parts Used in the 1A7A

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