|Bandwidth : DC to 1 MHz (Differential)|
|Input Impedance : 1MΩ 1%, 47pf|
|Calibrated ranges from 10 μV to 10 V/div in 19 steps
|Selectable upper and lower -3 dB points,
|10 μV/Hour DC Drift
|Out of Production 11/1/2000
The 1979 catalog lists the following recommended probes for the 7A22:
Passive : P6055, P6060, P6062B, P6101
Current : P6021, P6302/AM503
The 7A22 is a differential amplifier for use with all 7000-Series mainframes. Basic performance features are 10 μV/div to 10 V/div deflection factors, DC to 1 MHz bandwidth with selectable HF and LF -3dB POINTS, common mode rejection ratio of 100,000:1 at 10μV/div, DC coupled, differential signal range ± 1 V at 10μV/div and a DC OFFSET feature with ± 1 V range ± 100,000 div at 10 μV/div.
There are many factors which affect the usability of high-gain wideband differential amplifiers. Noise (if excessive) can make the high-gain positions unusable. Displayed noise (grounded inputs) is held to 16 μV at 10 μV/div, tangentially measured at full bandwidth. Since noise is related to bandwidth, the displayed noise can be greatly reduced with the HF -3dB POINT selector when the application allows. DC drift can also hinder measurements if the trace moves offscreen rapidly. Drift with time in the 7A22 is specified at 5 μV per minute and 10 μV per hour at 10 μV/div. Drift with temperature is 50 μV/°C or less. Low amplitude signals often ride a small DC component, perhaps a few millivolts, which would place a DC-coupled display offscreen at 10 μV/div. There are three ways to reject this DC voltage in the 7A22:
(1) AC coupled input if the signal frequency is high enough to be unaffected (2 Hz, LOWER -3dB POINT).
(2) AC coupling with the LF -3dB POINT selector which allows lower bandwidth selection down to 0.1 Hz.
(3) DC OFFSET which utilizes the differential feature and supplies an internal DC voltage to offset, or reject, the DC signal component.
These factors, and more, make the 7A22 well suited for measurements in the difficult low-amplitude low-frequency area.
Bandwidth - HF -3dB point; selectable in 9 steps (1-3 sequence) from 100 Hz to 1 MHz, accurate within 10% of selected frequency, risetime in 1 MHz position is 350 ns ±9%. LF -3dB point; selectable in 6 steps (1-10 sequence) from 0.1 Hz to 10 kHz, accurate within 12% of selected frequency, the switch also contains DC and DC with OFFSET positions. AC Coupled at input, 2 Hz or less.
Deflection Factor -- 10 μV/div to 10 V/div in 19 calibrated steps (1-2-5 sequence). Accuracy is within 2% with GAIN adjusted at 1 mV/div. Uncalibrated VARIABLE is continuous between steps and to at least 25 V/div.
Input R and C -- 1 MΩ within 1%; @47 pF.
Max Input Gate Current -- Differentially measured, 40 pA (+25°C) and 200 pA (+50°C) at 10 μV/div to 10 mV/div; 10 pA (+25°C) and 20 pA (+50°C) at 20 mV/div to 10 V/div. Single ended, one half the differential measurement. Display shift is ±4 div (+25°C) and ±20 div (+50°C) at 10 μV/div (AC couplet).
Signal and Offset Range
|Deflection Factor Settings
||10 μV to
|20 mV to
|0.2 V to
|2 V to
|Common-Mode Signal Range
||± 10 V
||± 100 V
||± 500 V
|MAX DC Coupled Input (DC + Peak AC at 1 kHz or less)
||± 15 V
||± 200 V
||± 500 V
|MAX AC Coupled Input (DC Voltage)
||± 500 V
DC rejection, at least 4 x 100,000:1
|DC Offset Range
||+1 V to
|+ 10 V to
|+ 100 V to
- 100 V
|+ 1000 V to|
- 1000 V
DC Stability -- Drift with Time (constant ambient temparature and line voltage): Short Term: 5 μV (P-P) or 0.1 div whichever is greater in any minute after 1 hour warm-up. Long Term: 10 μV (P-P) or 0.1 div whichever is greater in any hour after 1 hour warm-up. Drift with Ambient Temperature (constant line voltage) is 50 μV/°C or less.
Displayed Noise -- 16 μV or 0.1 div (whichever is greater) at maximum bandwidth, source resistance 25Ω or less, measured tangentially.
Overdrive Recovery -- 10 μs or less to recover within 0.5% of zero level after removal of a test signal applied for 1 s (signal amplitude not to exceed differential dynamic range). A front panel OVERDRIVE light indicates and overdrive condition is being approached.
|1X and 10X||P6052|
above excerpt from 1973 Tektronix Products Catalog
Functions of Controls and Connectors
INPUT OVERDRIVE indicator lamp turns on to indicate excessive differential drive to the input amplifier stage. Lights when the differential dynamic range between input connectors is exceeded.
VOLTS/DIV - Nineteen position switch used to select the calibrated deflection factors.
VARIABLE (CAL. IN) - Two-position switch activated by the VARIABLE knob to select calibrated or uncalibrated deflection factors. At the IN position, the VARIABLE control is inoperative and the deflection factor is calibrated. When pressed and released, the knob moves outward to activate the VARIABLE control for uncalibrated deflection factors. The uncalibrated position provides continuously variable uncalibrated attenuation between the calibrated deflection factors and extends the deflection factor to at least 25 Volts/Div.
GAIN - Screwdriver adjust control to se the CRT display scale factor to agree with the VOLTS/DIV switch indication. Adjusted for proper deflection with the VOLTS/DIV switch set to the 1 mV position.
POSITION - The control that vertically positions the trace or display.
IDENTIFY - Momentary contact, push-button switch, concentric with POSITION. Will cause the trace, representing the output of the Type 7A22, to move a small amount when pressed. Aids in identifying the Type 7A22 trace when multiple traces are displayed.
HIGH FREQUENCY -3dB POINT - Nine position switch to select the approximate high frequency -3 dB point. The switch positions are: 100 Hz, 300 Hz, 1 kHz, 3 kHz, 10 kHz, 30 kHz, 100 kHz, 300 kHz, and 1 MHz.
LOW FREQUENCY -3dB POINT - Eight position switch to select DC coupling or the approximate low frequency -3 dB points. The switch positions are: DC OFFSET, DC, .1 Hz, 1 Hz, 10 Hz, 100 Hz, 1 kHz, and 10 kHz.
+ INPUT - Signal input connector. Positive input produces deflection upward.
- INPUT - Signal input connector. Positive input produces deflection downward.
AC-GND-DC - A miniature illuminated push-button type switch (One switch for each input connector). The buttons are interlocked so that only one button may be depressed at one time. When the 'AC' button is depressed, the signal is coupled through 0.1 μF to the input Amplifier and only the varying component of the input signal is amplified.
When the 'DC' button is depressed, the signal is coupled directly to the input Amplifier and the entire input signal, both AC and DC, is amplified. When the 'GND' button (or none of the buttons) is depressed, the signal is coupled through 0.1 μF and trhough 1 MΩ to ground. The Amplifier Input is grounded in this condition.
NOTE : The following two controls are operative only when the LOW FREQENCY -3dB POINT switch is set to DC or DC Offset.
STEP ATTEN DC BAL (DC MODE ONLY) - Front panel control for DC balancing the amplifier input stage. With no signals applied to the input connectors, the control is adjusted for no trace shift as the VOLTS/DIV switch is moved from the 10 mV position to the 10 μV position.
DC OFFSET (DC OFFSET mode only) - Coarse and fine controls to provide internal offset bias while maintaining the differential capability. Available range of the offset bias depends upon the settings of the VOLTS/DIV switch, and is indicated by shaded gray bands (OFFSET RANGE) around the VOLTS/DIV switch.
Steps 1 through 5 in the following procedure are intended to help place the trace on the screen quickly and prepare the unit for immediate use. Steps 6 through 8 are used to chek the GAIN adjustment. These steps along with those remaining are intended to demonstrate some of the basic functions of the Type 7A22.
1. Insert the unit into the oscilloscope plug-in compartment.
2. Set the Type 7A22 front-panel controls as follows:
|HIGH FREQUENCY -3 dB POINT||1 MHz|
|LOW FREQ -3 dB POINT||DC|
|AC-GND-DC (+ INPUT)||GND|
|AC-GND-DC (- INPUT)||GND|
|STEP ATTEN DC BAL||Midrange|
3. Turn the oscilloscope intensity control fully counterclockwise and turn the oscilloscope Power ON. Preset the time-base and triggering controls for a 0.5 ms sweep rate and automatic triggering.
4. Wait about five minutes for the Type 7A22 and the oscilloscope to warm up.
About five minutes is sufficient time for warmup when using the Type 7A22 for short-term DC measurements. For long-term DC measurements using the lower deflection factors, allow at least one hour.
5. Adjust the Intensity control for normal viewing of the trace. The trace should appear near the graticule center.
6. Using the POSITION control, position the trace 2 divisions below graticule center.
If the maximum input voltage rating in the 10 μV to 10 mV range of the VOLTS/DIV switch is exceeded, the inputs are diode-clamped to fixed voltages of approximately + 16.5 volts and/or -16.5 volts and damage to the signal source is possible. If the signal source can supply more than 1/16 A of current, the input protective fuse(s) will open. An open input fuse is indicated by the lighting of the INPUT OVERDRIVE indicator with the input coupling switches set to GND.
7. Apply a 4 mV peak-to-peak calibrator signal through a coaxial cable to the + INPUT connector on the Type 7A22.
8. For DC coupled, single-ended operation, set the + INPUT AC-GND-DC coupling switch to DC. The display should be square waves 4 divisions in amplitude with the bottom of the display at the reference established in step 6.
9. For AC coupled, single-ended operation, reposition the display with the Type 7A22 POSITION control to place the bottom of the display at the graticule center line.
10. Set the _ INPUT AC-GND-DC coupling switch to AC and note that the display shifts downward about 2 divisions to its average level.
11. Disconnect the coaxial cable from the + INPUT connector. Connect a dual input connector to the + INPUT and - INPUT connectors. Connect the coaxial cable from the Calibrator to the dual input connector.
12. For AC coupled differential operation, set the -INPUT AC-GND-DC coupling switch to AC. The calibrator signal is now coupled to both inputs as a common-mode signal. A straight line display should be observed, since the common-mode is being rejected.
above excerpt from 7A22 Maintenance Manual (US Army version)
|1- 1||366-1059-00||Pushbutton : Gray (Identify)|
|1- 2||366-1077-00||Knob : Gray (Position-large outer)|
|1- 7||366-0392-02||Knob : Gray (step-atten/dc bal)|
|1-10||366-1166-00||Knob : Red (Var Volts/div)|
|1-11||366-1057-00||Knob : Gray (Volts/Div - large ourter)|
|1-12||366-0379-00||Knob : Gray, Mode (HF-3db point)|
|1-13||366-0379-00||Knob : Gray, Mode (LF-3db point)|
|1-14||366-1084-00||Knob : Gray (offset-fine small inner)|
|1-15||366-1101-00||Knob : Gray (offset coarse-larger outer)|
|1-38||366-1058-07||Knob : Latch (7A22 pull tab)|
|1- 3 (R430/S622)||311-0888-01||Res, Var, Nonwir : 2 x 10K, 0.5W (Clarostat D381S-CM40098) (position)|
|1- 8 (R258)||311-0467-00||Res,Var,Nonwir : 100K, 20%, 0.5W (CTS Keene 300SF-41334) (step atten/dc bal)|
|1-16 (R270)||311-0889-00||Res, Var, ww : 5K, 1W (Spectrol 162-214) (offset coarse)|
|1-23 (R265)||311-0887-00||Res,Var,Nonwir : 50K, 10%, 0.5W (offset fine)|
|2-21 (R540)||311-0702-00||Res,Var,Nonwir : 250 ohm, 10%, 0.5W (Clarostat 382-CM39823) (gain)|
|2-62 (R535/S535)||311-0949-00||Res,Var,Nonwir : 2K,10%, 0.5W w/ switch (A-B WA1G040S202UA) (volts/div var)|