The Tektronix 3A9 is a differential amplifier plug-in introduced in 1969 for 560-series scopes. It shares similarities with the 3A10 transducer amplifier and the 7A22 from the 7000 series and 5A22N from the 5000-series scopes.
The 3A9 features a variable high-frequency cut-off from 100 Hz to 1 MHz and a variable low-frequency cut-off from DC to 10 kHz. When DC coupled, the 3A9 provides a variable offset voltage. The common mode rejection is 100,000:1.
|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)|
|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|
The differential amplifier design is a variant of the 1A7A circuit, also used with modifications in the 3A10, 7A22, 5A22N oscilloscope plug ins, and 5030/5031 scopes. The AM502 and the 26A2 for the 2601 mainframe use BJTs for the offset current sources instead of JFETs. The 26A2 adds a common mode signal circuit which is connected to a LEMO probe connector.
The front-end of the 3A9 starts with a differential pair formed by the two N-channel JFETs in a 151-1027-00, Q133.