7A19

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The Tektronix 7A19 is a one-channel 600 MHz vertical amplifier plug-in for 7000-series scopes, designed by Thor Hallen and introduced along with the 7904 mainframe in late 1971/early 1972 (note 1).

Operation

The 7A19 has no variable gain control. An option (#4) was available that added a variable signal delay (± 0.5 ns implemented using a mechanically variable passive delay line), intended to match timing between multiple channels.

The pre-charge setting on the input coupling switch is intended for situations where there might be residual charge on the input coupling capacitor that could overload the input. To use it, one sets the switch to PRE-CHG before connecting the input signal, then waits two seconds before switching to AC (LF point is 1 kHz). The PRE-CHG setting also serves as a ×100 attenuator having a 5 kΩ input impedance in series with 2 μF, extending LF cutoff down to 20 Hz. In the AC GND position, the input is disconnected from the amplifier and terminated in a capacitively coupled 50 Ω load.

Key Specifications

Input impedance	50 Ω
Bandwidth	600 MHz (500 MHz in 7904)
Deflection	10 mV/Div to 1 V/Div, 1—2—5 sequence. Pre-charge circuit may be used as a calibrated ×100 attenuator.
Maximum input	2 W average or 50 Div, in AC mode 100 V DC+peak AC
Variable delay (Opt.4)	-0.5 ns to +0.5 ns

Internals

The 50 Ω input impedance of the 7A19 is provided by a pair of 100 Ω resistors in parallel. The resistors are protected by a pair of fuses in parallel. The manual explains that the motivation for using two fuses in parallel is to minimize the effect of the series impedance of the fuses.

The only active device in the vertical signal path of the 7A19 is an 155-0068-00 amplifier hybrid, (U40, Tek internal part number H101). A second 155-0068-00 is used in trigger signal path of the 7A19. The trigger signal path is almost identical to the vertical signal path.

Notes

See 7A11 and John Addis, Good Engineering and Fast Vertical Amplifiers, in Jim Williams (Ed.), Analog Circuit Design: Art, Science and Personalities (1991), p.114, and Tektronix New Products 1972 brochure.