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The Tektronix Type 1A7 is a high-sensitivity differential plug-in for 500-series scopes. It senses down to 10 μV/Div, either AC or DC-coupled. It's possible to apply up to ± 300 mV offset to the reading while maintaining sensitivity. Upper and lower cutoff frequency is selectable on the front panel. Maximum bandwidth is 500 kHz, and common-mode rejection is 50,000 to 1.

Type 1A7's front end is a matched quad of 7586 nuvistors, with two in parallel - to reduce noise - on each input. These tubes are in temperature-equalizing housings, and mounted on a rubber-isolated subchassis. The "coarse" balance adjustment controls the relative heater voltages on the 7586's.

Type 1A7 (initially named Type F) was designed by John Addis and introduced in 1966.

Type 1A7A

In 1968, the 1A7 was superseded by the FET-equipped Type 1A7A (designed by Thor Hallen), which also doubled common-mode rejection and bandwidth (to 1 MHz).

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 offset current sources.

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


Deflection 10 μV/Div to 10 V/Div in 1–2–5 sequence
Input impedance 1 MΩ // 47 pF (either input)
     — 1A7
Bandwidth 1 MHz, LF limit switchable DC, 0.1 Hz to 10 kHz in ×10 steps, HF limit switchable 100 Hz to 100 kHz in ×3/×10 steps, and 500 kHz; AC coupling 1.6 Hz
     — 1A7A
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