Tektronix 1A4 50 Mhz 4-channel Amplifier (1969)

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BAMA 1A4 Free Manual and Schematic Download Site
Quick Specifications / Photos
Detailed Specifications
Operating Instructions
Misc. Part Numbers

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Tek Catalog CostLow BidHigh Bidaverage
$825 (1969)
$1150 (1973)
$1275 (1974)
$63.00 12/23/02 #3100749448 spidermanz (10 bids)
$51.00 3/16/03 #2514882365 spidermanz (7 bids $10 start)
$6.00 11/28/04 #3854977248 janifree (2 bids $5 start) (dirty,noisy,untested)
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  • DC to 50 MHz bandwidth (in 547)
  • 10 mV/cm to 20 V/cm in 11 calibrated steps for each channel
  • 7ns Risetime (in 547)
  • 1 MΩ, 20pF Input

  • This is a four channel amp, and one that works very well. With the right scope (like a 547) it has a bandpass of up to 50 MHz. It can chop, alt, or add in any possible way between the four channels, and handy "ident" buttons help you identify what's what when you have four traces on screen.
    The Tektronix Type 1A4 is a four-channel 50 MHz plug-in unit designed to operate at maximum bandwidth in the Type 544, 546, 547, and 556 Oscilloscopes (including rackmounts). The unit provides four-channel operation for all 530-, 540-, 550-, and 580-series oscilloscopes. It can also be used in conjunction with other oscilloscopes and devices through the use of a Tektronix Type 127, 132, or 133 plug-in power supply.

    The Type 1A4 contains four identical fast-rise calibrated preamplifier channels. Each channel has its own input selector, attenuator, polarity and position controls which allows each display to be adjusted for optimum viewing. Basic deflection factor for each channel is 10 mV/cm.

    The unique electronic switching logic of the Type 1A4 provides the versatility of two independent dual-trace units connected to the inputs of a third dual-trace unit without sacrificing bandwidth. For example, displays composed of channel 1 minus channel 2 can be chopped or alternated with channel 3 minus channel 4. As another example, the unit can be used in a "double-added" mode (channels 1 and 2 added to channels 3 and 4).


    The following performance requirements (center column data) apply over an ambient temperature range of 0°C to +50°C after a warm-up time of 20 minutes.

    CharacteristicPerformance RequirementSupplemental Information
    Deflection Factor10 mV/cm to 20 V/cm in 11 calibrated steps for each channel.Steps in 1-2-5 sequnce.
    Deflection AccuracyWithin ±3% of indicated deflection with VARIABLE V/CM control in the CAL (detent) positionWith gain correct at 10 mV/cm.
    Added Accuracy±1% with V/CM switch set to .01.
    Variable Deflection FactorUncalibrated deflection factor at least 2.5 times the V/CM switch indication. This provides an uncalibrated deflection factor of at least 50 V/cm in the 20 V/cm position.
    Frequency Response (not more than -3 dB) using the Type 1A4 with Tektronix Oscilloscopes:
    544, 546, 547, or 556
    DC to 50 MHz
    581, 581A, 585 or 585A
    DC to 50 MHz with Type 81A Plug-In AdapterDC to 33 MHz with Type 81 Plug-In Adapter
    541, 541A, 543, 543A, 543B, 545, 545A, 545B or 555
    DC to 33 MHz
    DC to 30 MHz
    DC to 27 MHz
    531, 531A, 533, 533A, 535 or 535A
    DC to 15 MHz
    DC to 11 MHz
    Risetime (calculated minimum) using the Type 1A4 with Tektronix Oscilloscopes:

    544, 546, 547 or 556
    7 ns Calculated using this formula:
    Risetime = 0.35/(Frequency)²
    581, 581A, 585 or 585A
    7 ns with Type 81A Plug-In Adapter11 ns with Type 81 Plug-In Adapter
    541, 541A, 543, 543A, 543B, 545, 545A, 545B or 555
    11 ns
    12 ns
    13 ns
    531, 531A, 533, 533A, 535 or 535A
    24 ns
    32 ns
    Input Characteristics:
    DC Resistance
     1 MΩ, ±1%.
     20 pF, ±5%
    Maximum Input Voltage 600V combined DC and peak AC.
    Input Coupling Modes AC or DC, selected by front-panel switch. GND position internally disconnects the signal and grounds the amplifier input circuit to provide a zero reference for the trace.
    AC Low-Frequency Response Typically -3 dB at 2 Hz direct. 0.2 Hz with 10X probe.
    Vertical Display Modes Any two channels alternated, chopped, or added in any combination. Four channels (Channels 1 and 2 alternated, chopped, or added with Channels 3 and 4).
    Chopping Repetition Rate400 kHz, ±20%To show successive 2.5 μs (approx.) segments of each trace.
    Chopped Blanking Pulse Width 0.4 to 0.8 μs, measured at the 50% amplitude level.

    Chopped transient blanking occurs in all oscilloscopes except Types 536, 551, 581A and 585A
    Common-Mode Rejection Ratio>=20:1 for signals from DC to 10 MHz.Checked with 10 MHz common-mode sine-wave signals up to 10-cm in amplitude.
    Polarity Inversion Signal in any channel can be inverted.
    Normal/Invert Trace Shift<1 cm at an ambient temperature of 25°C, ±5°C.When VAR BAL controls are adjusted for no trace shift.
    Trigger Selector Balance Trace Shift<=0.2cm at an ambient temperature of 25°C, ±5°C.
    Trace Drift with Time (after warm up), V/CM switch at .01 ±2 cm in any hour after a 20-minute warm up at 25°C, ±5°C.
    Channel Isolation:
    >=5,000:1 for signals from DC to 10 MHz.
    >=50:1 for signals from DC to 20 MHz
    >=0.5V/cm of displayed signal.SIGNAL OUTPUT connector unterminated.
    <=20 Hz to >=10 MHz unterminated in all modes except chopped.
    <=20 Hz to 500 kHz (±20%) in chopped mode.
    With gray-on-white wire connected to pin M on the Logic board.
    Output Impedance
     Approximately 50 ohms.
    Output Coupling
     DC Level: 0V, ±1 V at output stage and AC-coupled in preceding stages.

    Above excerpt from Textronix Type 1A4 Plug-In Instruction Manual


    A brief description of the function or operation of the Type 1A4 front- and rear-panel controls and connectors is provided here. On the front panel the controls and connectors are logically arranged so the signal path flow for each channel is from the Input connector upward. Channel 1 and 2 signal paths converge into the Ch 1 & 2 MODE switch, Channel 3 and 4 signal paths convere into the Ch 3 & 4 MODE switch, and the outputs from both of these switches are then applied to the DISPLAY switch. Since the controls are arranged in this manner, the listing of the controls in this manual usually follows the same plan.


    The following Input connector and controls are identical for each channel.

    InputSignal input connector for the channel.
    AC-GND-DCThree-position lever switch to provide a choice of AC or DC input coupling for the applied signal. The GND position internally disconnects the signal and grounds the channel-amplifier input circuit to provide a zero reference for the trace.
    V/CMAn eleven-position switch to select the calibrated deflection factors from 0.1 V/CM to 20 V/CM in a 1-2-5 sequence.
    VARIABLEVaries the deflection factors between calibrated settings by at least a 2.5:1 ratio, allowing overlapping and continuously variable deflectio factors from 0.1 V/Cm to at least 50 V/CM. This control has 360° rotation and a detent position for the CAL (calibrated) position.
    INVERTWhen the INVERT knob is pulled outward, the display polarity is inverted with respect to the applied signal; when the INVERT knob is pushed in, the display presents the same polarity as the polarity of the applied signal.
    VAR BALScrewdriver adjust potentiometer for varying the channel amplifier balance so the display DC level will remain stationary when turning the VARIABLE control.
    POSITIONPositions the trace or display vertically on the CRT.
    IDENTIFYA push-button switch that momentarily shifts the trace display upward a small amount to identify the respective channel.
    GAINScrewdriver-adjust potentiometer for adjusting the common gain of all channels simultaneously. Compensates for slight gain variations between oscilloscopes.

    Other Controls and Connector

    Ch 1 & 2 MODEA five-position 360°-rotation switch that selects the mode of operation as follows:
    CHANNEL 1 - Displays Channel 1 only.
    ALT - Dual-channel alternate mode of operation (triggered electronic switching between channels during the sweep retrace interval).
    CHOP - Dual-channel chopped mode of operation (free-running electronic switching of channels at a rate of approximately 2 μs displayed time to 0.5 μs blanked time).
    ADD - Permits adding the outputs of the two channels algebraically.
    CHANNEL 2 - Displays Channel 2 only.
    Ch 3 & 4 MODESame as Ch 1 & 2 MODE switch but selects the mode of operation for Channels 3 and 4
    DISPLAYA five-position switch that selects the type of display as follows:
    1 & 2 - Displays Channel 1 or 2, or 1 and 2 depending on position of Ch 1 & 2 MODE switch.
    ALT - Provides an alternating diaplay between dual Channels 1 & 2 and Channels 3 & 4. A 547 TRACE SLAVING switch on the rear panel provides for sweep-switching slave operation when the Type 1A4 is operated in the Type 547 Oscilloscope. When this rear-panel switch is set to LOCK, Channels 1 and 2 are slaved to A sweep and Channels 3 and 4 are slaved to B sweep.
    CHOP - Provides chopped operation between Channel 1 and 2 composite signal and Channel 3 and 4 composite signal.
    ADD - Adds the outputs of Channel 1 and 2 composite signal to Channel 3 and 4 composite signal.
    3 & 4 - Displays Channel 3 or 4, or 3 and 4 depending on position of Ch 3 & 4 MODE switch.
    SIGNAL & TRIGGER SOURCEA four-position switch that selects the channel signal to be applied to the SIGNAL OUTPUT connector and to the plug-in internal trigger for oscilloscopes with plug-in trigger capabilities.
    SIGNAL OUTPUTProvides an output signal to be used for triggering purposes or cascade operation.

    Above excerpt from Textronix Type 1A4 Plug-In Instruction Manual
    366-0215-01Knob, lever, charcoal AC-GND-DC
    366-0365-00Knob, red - VARIABLE AC-GND-DC
    366-0322-00Knob, charcoal - DISPLAY
    366-0366-00Knob, red - IDENTIFY
    366-0322-01Knob, charcoal MODE
    366-0347-00Knob, charcoal - POSITION
    366-0322-00Knob, charcoal - V/CM
    366-0140-00Knob, red - SIGNAL & TRIGGER SOURCE
    SW1(2-2,27,52,77)260-0805-00Switch, Lever - AC-GND-DC
    SW300,310,320,330260-0723-00Switch, Slide - PULL TO INVERT
    R75 ??(VARIABLE)
    SW100260-0802-00Switch, Rotary - SIGNAL & TRIGGER SOURCE
    1-8(SW475)260-0802-00Switch, Unwired DISPLAY (s/n
    1-8(SW475)260-0802-01Switch, Unwired DISPLAY (s/n >=B050000)
    1-36(R379)311-0651-00Resistor, variable 10K - GAIN
    1-2,13(SW415,445)262-0803-00Switch, Unwired MODE
    1-19,23,26,29(R305,15,25,35)311-0652-00Resistor, variable 2 x 5K - POSITION
    2-1,26,51,76 (SW15)260-0806-00Switch, Unwired V/CM
    1-31 (R60)311-0650-00Resistor, variable 5 K - VAR BAL