7A18: Difference between revisions

Revision as of 10:41, 30 October 2020

The Tektronix 7A18 is a general-purpose 75 MHz dual-trace vertical plug-in for 7000-series scopes. Model 7A18N is identical except it omits the readout circuits.

Option 06 (first offered in 1975 catalog) adds offset voltage controls giving ±200 Div offset range. This option replaces the IDENTIFY buttons with DC offset controls and adds a fourth "DC offset" position to the input coupling switch.

The 200 MHz 7A26 and 400 MHz 7A24 share the same front panel layout and operation.

The 7A18 uses a discrete front-end followed by M36 channel switch ICs for the vertical and trigger signals.

Key Specifications

Input impedance	1 MΩ // 20 pF
Deflection	5 mV/div to 5 V/div in 1–2–5 sequence, 2%
Bandwidth	0 – 75 MHz (DC), 10 Hz – 75 MHz (AC)
Noise	< 300 μV in 5 mV/Div
Option 06 offset range	±200 Div equiv. from ±1 V in 5 mV/Div range up to ±200 V in 1 V/Div range (above that limited by maximum input voltage)
Features	Mode: CH1 only, CH2 only, Add CH1+CH2, Alternating, Chopped. CH2 can be inverted. Input sockets with contact ring for probe ×10 / identify information No bandwidth limiter switch
Weight	1.4 kg

Prices

Year	1971	1976	1980	1984	1990
Catalog price	$535	$615	$915	$1,250	$1,790
2018 value	$3,300	$2,700	$2,770	$3,000	$3,420

Repair issues

The pins of the attenuator modules are connected to conductive traces on the ceramic substrate inside by low-temperature soldering, which can go bad. Re-seating the module can temporarily restore the internal contact but will usually not fix the problem permanently. Repair is possible by opening the click-locked lid and carefully resoldering.

Pictures

7A18 Front
7A18A Front
7A18A left side. The step attenuators can be seen on the left, the amplifier board on the right.
7A18A right side. The circuit boards on top carry the readout circuitry.
7A18 attenuator opened. One of the attenuation R/C modules has been unplugged to reveal the switch contacts.
A 7603 with two 7A18s
7A18 in 7613 mainframe

Option 06

7A18A Opt.06 Front. AC/GND/DC switches have an extra rightmost "DC Offset" position enabling the offset controls.
7A18A Opt.06 left side (rear). Note the two blue 10T-potentiometers for offset voltage adjustment.
7A18A Opt.06 - offset controls take the place of the Identify buttons on the standard model.

@@ Line 20: / Line 20: @@
 The 200 MHz [[7A26]] and 400 MHz [[7A24]] share the same front panel layout and operation.
-The 7A18 uses the [[M036|M36]] channel switch IC for the vertical and trigger signals.
+The 7A18 uses a discrete front-end followed by [[M036|M36]] channel switch ICs for the vertical and trigger signals.
 {{BeginSpecs}}