7A22

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The Tektronix 7A22 is a single channel differential vertical amplifier for the 7000 series mainframes, designed by Val Garuts and produced from about 1969 to 1991. Specifications and controls are similar to the 26A2 and the 3A9 from the 560 series but without current probe input nor front panel signal output.

The 7A22's input sensitivity reaches down to 10 μV/Div. Bandwidth is 1 MHz, the upper 3 dB limit can be reduced in ×3 steps down to 100 Hz (to eliminate noise, inter alia), and the lower bandwidth can be raised in ×10 steps from 0.1 Hz to 10 kHz. A separate control optionally supplies an internal DC voltage to offset the DC signal component. Even in the most sensitive ranges (10 μV/Div to 10 mV/Div), common-mode voltage can be ±10 V. Input resistance is 1 MΩ, but for high source resistance DC coupled measurements, one can disconnect the internal gate return resistors of the input FETs, at the disadvantage of disabling the 20 mV/div and higher ranges.

Applications include audio, biological signals, sensors etc.

An example application is found in Jim Williams' LT Application Note 124 – see Appendix D for a comparison of differential amplifiers.

Key Specifications

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
Deflection	10 μV/Div to 10 V/Div in 1–2–5 sequence
Input impedance	1 MΩ // 47 pF (either input)
Signal ranges

Range	Differential signal	DC Offset	Common mode
10 μV/Div to 10 mV/Div	±1 V	±1 V	±10 V
20 mV/Div to 0.1 V/Div	±10 V	±10 V	±100 V
0.2 V/Div to 1 V/Div	±100 V	±100 V	±500 V
2 V/Div to 10 V/Div	±1000 V	±1000 V	±500 V

Internals

The differential amplifier design is a variant of the 1A7A circuit, also used with modifications in the 3A9, 5A22N, AM502, and 5030/5031 (26A2 too?).

John Addis says:

The 1A7A (designed by Thor Hallen) and the 7A22 (designed by Val Garuts) used essentially the same circuit. Exactly who came up with the brilliant input circuit is lost to history. The 1A7A came out first, but Thor had worked as evaluation engineer for Val Garuts (and is listed that way in the 7A22 Engineering Instrument Specification). Val does not remember who created the circuit, and Thor died in 2002.

Prices

Year	1970	1971	1980	1984	1990
Catalog price	$500	$500	$1,060	$1,590	$2,260
In 2023 Dollars	$3,900	$3,800	$3,900	$4,700	$5,300

Pictures

Plug-in

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  7A22 front view

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  left side

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  left side (with cover)

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  right side

Measurements

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  7A22: 1 kHz, 130 μV_p-p triangle, BW=1 MHz

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  7A22: 1 kHz, 130 μV_p-p triangle, BW=100 kHz

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  7A22: 1 kHz, 130 μV_p-p triangle, BW=10 kHz

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  7A22: 1 kHz, 130 μV_p-p triangle, BW=1 kHz

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  15 μV p-p triangle wave displayed in variable-persistence storage mode on a 7613 for noise filtering