7A16P

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The Tektronix 7A16P is a single channel, programmable, vertical amplifier for 7000-series digitizing mainframes. All functions of the 7A16P can be remotely programmed via the GPIB 7000-series main interface bus, with exception of the variable gain control and the probe identify switch. It is special among the 7000-series vertical amplifiers since it offers a switchable 1 MΩ/50 Ω input impedance, only paralleled by the 7A42. The 7A16P is also unique as it has two input BNC connectors, but is strictly a single channel plugin, having a switch that routes one of the BNC connectors to the amplifier circuits. This feature is handy in remote-controlled digitizing applications.

It was mainly intended for use in the 7612D and the 7912 family, but can also be used in the 7854 if paired with a 021-0374-00 and internally modified by adding cables for a 18 pin header and setting jumpers correctly. It is not recommended to use the 7A16P in any conventional 7000-series mainframe since it expects +5.1 V at pins B27 and A9 of the mainframe interface, and shorts them together. A9 is the 5V light pin on conventional mainframes, and its current rating might be too low for successful operation of the 7A16P. In the 7854 the "Control Illumination" switch at the rear must be at "high" to supply 5V at A9.

Key Specifications

Bandwidth 1 MΩ	0 – 150 MHz
Bandwidth 50 Ω	0 – 200 MHz
Deflection	10 mV/Div to 5 V/Div in 1–2–5 sequence
Input impedance	1 MΩ
Features	Two BNC inputs 20 MHz bandwidth limit switch Invert switch Probe multiplier / Identify switch sensing inputs

Internals

The input stage of the 7A16P contains miniature relays switching between the two available input connectors and selecting the AC and DC coupling modes. Another relay is used to enter a 50 Ω shunt if the corresponding input impedance is selected. Relays then select an optional 10x attenuator before entering the input buffer. This buffer contains an AC coupled MOSFET common drain amplifier and a DC coupled operational amplifier, configured in a feed-beside scheme. Gain switching is accommodated by several junction FETs to enter another 10x attenuator in front of the MOSFET buffer, and to enter 2x and 5x low impedance attenuators after the input buffer.

The digital circuitry is build around a Motorola 6800 processor with several MC6821 to drive the switches of the analog circuits and interfacing the modified 7000-series internal GPIB bus.