Tektronix DD501 Digital Delay

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Quick Specifications / Photos
Detailed Specifications
Operating Instructions
Misc. Part Numbers

Samples of e-Bay Prices
Tektronix Catalog CostLow BidHigh Bidaverage
$725 (1977)
$1170 (1982)
$1385 (1985)
$42.00 8/8/01 #1623029262 ridgeeq
$39.80 8/16/01 #1625857623 jshank
$46.07 9/6/01 #1633444997 jshank
$89.00 9/17/01 #1637351196 baron11
$33.50 10/22/01 #1650783809 j.a.
$76.00 10/31/01 #1655265863 hayes3812
$21.71 8/8/04 #3831389716 toynation1 (6 bids $10 start) (untested)
$50.00 8/10/04 #3831798648 boss1 (1 bid) (untested)
$30.99 8/16/04 #3832788247 tbp1 (2 bids $30 start) (working)
$11.50 9/3/04 #3836770001 sams995 (2 bids $10 start) (untested)
$16.00 7/6/05 #7527504731 boss1 (2 bids $15 start) (untested)
* $16.25 3/18/06 #7599181971 superpicklekongkiller (3 bids $14 start) (untested)
$16.99 4/14/06 #7608075644 boss1 (2 bids $16.00 start) (untested - corners chipped)
$42.00 (+$13 ship) 12/15/06 #330060342024 ridge_equipment (3 bids $34.99 start) (lights up-untested otherwise)
$26.00 (+~$15 ship) 1/11/08 #180201617610 tjs6121 (5 bids $0.99 start) ("great working condition")
$32.75 (+$9.26 ship) 7/16/08 #250268866983 apple3_14 (6 bids $9.99 start) (powers on)
$19.99 (+~$19 ship,handling) 11/10/10 #390259182359 esssurplus (1 bid) (untested)

  • Delay to 99,999 Events
  • Divide by N up to 20 MHz
  • Pulse Counting to 65 MHz
  • Trigger Level Range +1.0V to -1.0V
  • Pulse Width (minimum) 5 ns
  • Trigger View Output of at least 0.5V


    The DD 501 Digital Delay is an events counting plug-in unit designed for use in a TM 500-Series Power Module mainframe. Separate external trigger signals are connected to the EVENTS and START INPUT connectors allow up to 99,999 events to be counted. That is, the unit counts a predetermined number of events, from 0 to 99,999, selected by the front-panel thumb-wheel switches. The last event counted generates a trigger pulse to the DLY'D TRIG OUT connector on the front panel. Delay by event is particularly useful in troubleshooting asynchronous logic systems. The DD 501 can also function as a frequency divider when the same signal is applied to both inputs.

    The DD 501 can be used in a "counted burst" mode with pulse or function generators that can be synchronously gated. This provides the ability to dial up the number of pulses you want in a burst for applications with shift registers, memories, data communications, process control, or any system requiring an exact number of pulses or waveforms. A jumper inside the DD 501 converts the DLY'D TRIG OUTPUT to a delay interval (gate) waveform for this application. TEKTRONIX generators capable of being gated by the DD 501 are the FG 501, FG 502, FG 504 and the PG 508.

    Other DD 501 applications include ranging for radar, sonar, ultrasonics, or laser. By using the proper frequency clock, the numbers dialed up can represent miles, yards, kilometers, etc. In systems requiring precision timing. several DD 501s and a reference clock can provide precise thumbwheel-selectable repetition rates, delays, pulse widths, or timing intervals.

    Electrical Characteristics

    CharacteristicPerformance RequirementSupplemental Information
    Input Resistance and Capacitance 1 MΩ paralleled with 20 pF (variable)
    Slope+ or -, selectable
    Sensitibity85 mV p-p minimum at 30 MHz; 120 mV p-p minimum at 65 MHz.
    Trigger Level Range-1.0 V to + 1.0 V
    Frequency Response0 to 65 MHz
    Pulse Width (minimum)5 ns
    TRIG VIEW OutputAt least 0.5 VPermits viewing of all shaped triggers
    Source Impedance 200 Ω or less
    Trigger LEVEL IN/OUT Monitor Jack Probe-tip jack -- allows monitoring comparator voltage of preset or trigger level to within 25 mV.
    Source Impedance Approximately 1 kΩ
    TRIG'D Indicator 
    EVENTSVisual indication of triggering
    STARTVisual indication that start gate is open
    LEVEL Controls 
    0 Volt Trigger Level Within 30° of mechanical zero
    START Pulse Lead Time Simultaneous or ahead of the EVENTS pulse
    Recycle Time50 ns or lessParalleling START and EVENTS INPUTS determines maximum ÷ N + 1 frequency
    RESETResets start gate and events counter 
    0 to 99999
    Throughput Time30 ns or less
    Delayed Trigger Out
    Pulse Width (max)

    Up to 5 ns greater than the events pulse width
    AmplitudeAt least 1 V into 50 ohmsFrom +0.8 to +2.2 V into 3 TTL loads (approximately 5 mA)
    Source ImpedanceLogic 1 approximately 50 ohms
    Logic 0 approximately 200 ohms
    TRIG'D IndicatorIndicates trigger out 

    above excerpts from 1977 TM 500 brochure and DD 501 DIGITAL DELAY (with Options) Instruction Manual


    Signal Connection

    The DD 501 unilizes dc coupling into the EVENTS and START trigger INPUT connectors. In general, probes offer the most convenient means of connecting signals to the DD 501 trigger inputs. Tektronix probes are shielded to prevent pickup of electrostatic interference. A 10X attenuation probe offers a high input impedance and allows the circuit under test to perform very close to normal operating conditions. Also, a 10X probe attenuates tha input signal 10 times.

    Tektronix probes are designed to monitor the signal source with minimum circuit loading. The use of a probe will, however, limit the maximum trigger frequency range. To obtain maximum trigger bandwidth when using probes, select a probe capable of compensating the input capacitance. Observe the grounding considerations given in the probe manual. The probe-to-connector adapters and the bayonet-ground tip provide the best frequency response.

    In high-frequency applications, which require maximum overall bandwidth, use a coaxial cable terminated at the output end in the characteristic impedance of the source. To maintain the high-frequency characteristics of the applied signal, use high-quality, low-loss cable. Resistive coaxial attenuators can be used to minimize reflection if the applied signal has suitable amplitude.

    High-level, low-frequency signals can be connected directly to the external trigger inputs with short, unshielded leads. When this method is used, extablish a common ground between the DD 501 and the associated equipment. The common ground provided by the line cords is usually inadequate. If interference is excessive with unshielded leads, use a coaxial cable or probe.

    The front-panel output signal from the DLY'D TRIG OUT connector should be connected to other equipment with 50 ohm coaxial cable. The cable should be terminated in 50 ohms to maintain the risetime and falltime characteristics of the signal.


    The input signal may have a wide variety of shapes and amplitudes, many of which are unsuitable as delay-initiating triggers. For this reason, these signals are first applied to a trigger circuit where they are converted to pulses of uniform amplitude and shape. This makes it possible to start the delay with a pulse that has a constant size, eliminating variations of the delay circuit operation caused by changing input signals. The trigger controls provide a means to select the START and EVENT pulses at any voltage level on either slope of the waveform.

    The trigger SLOPE and LEVEL control determine the slope and voltage of the input signal where the trigger circuit responds. Generally, the best point on a waveform for triggering is where the slope is steep, and therefore usually free of noise. Assuming a sine-wave input waveform, the steepest slope occurs at the zero-crossing point. This is the point selected for triggering when the LEVEL control is set to 0 (center). A more positive or negative point on the waveform is selected as the LEVEL control is rotated clockwise or counterclockwise respectively from 0 (toward + or - symbols on the panel).

    Before setting the trigger level, the desired slope should be selected. Adjust the START LEVEL control to the desired start trigger point. Then adjust the EVENTS LEVEL control to trigger the events pulse either simultaneously or after the start trigger pulse. The relationship between start and events triggering is monitored at the START and EVENTS TRIG VIEW connectors.

    Either LEVEL control can be preset to a fixed voltage level by adjusting the front-panel PRESET adjustment. Rotate either LEVEL control fully clockwise (into the detent), and set the PRESET screwdriver adjustment to the desired triggering voltage level.



    The EVENTS DELAY COUNT switch is a 5 decade, digital readout switch that increases or decreases the count at which a delayed pulse will occur. This switch selects the number of events to be counted. The delay count is displayed on the front-panel switch readout. The DLY'D TRIG OUT signal is delayed 1 count more that the EVENTS DELAY COUNT switch setting; that is, a switch setting of 00000 will count 1 event pulse, or a switch setting of 99999 will count 100,000 event pulses to produce a DLY'D TRIG OUT pulse.

    INPUT Connectors

    Individual front-panel connectors are provided for connecting the external trigger signals to the EVENTS and START trigger preamplifiers.

    EVENTS and START SLOPE Switches

    Determine the amplitude point on the trigger signal at which the circuit triggers. In the fully clockwise detent position, the circuit triggers at the amplitude point on the trigger signal selected by the PRESET screwdriver adjustment.

    LEVEL IN/OUT Connectors

    Individual front-panel pin jacks are provided to monitor the EVENTS and START dc level at which the triggering occurs.

    EVENTS TRIG'D Indicator

    Provides a visible indication that the Events circuit has received a trigger, and that an adequate trigger signal is applied.

    START TRI'D Indicator

    Provides a visible indication that the Start gate circuit has received a trigger, and is open, ready for the events count to begin.

    RESET Pushbutton

    A front-panel RESET button is provided to clear the EVENTS counter and reset the START circuit. The next START pulse will restart the EVENTS count at 00001. The RESET pushbutton allows the operator to reset the counter and start circuit when in long term count cycles or when a false trigger occurs.

    TRIG VIEW Connectors

    Individual front-panel probe-tip connectors are provided for monitoring the EVENTS and the START trigger pulse waveforms. The TRIG VIEW output signals are a representation of the input trigger signals repetition rates. The TRIG VIEW output pulse width is determined by the input waveshape and the triggering voltage level. For example, a sinewave EVENTS INPUT signal, set to trigger 2.5 microseconds before its peak, produces an output trigger width of 5 microseconds. Consequently, varying the trigger amplitude point on the input waveform will vary the output pulse width proportionally.

    DLY'D TRIG OUT Connector

    Provides a means of applying the shaped delayed trigger pulses to associated equipment. Output signals are generated as positive-going rectangular pulses coincident with the end of the delay interval. The DLY'D TRIG OUT pulse width will be identifal to the Schmitt-trigger pulse width, which can be monitored at the front-panel TRIG VIEW connector.


    Provides a visible indication when a delayed trigger output has occurred.

    above excerpt from DD 501 DIGITAL DELAY (with Options) Instruction Manual

    1-2366-1576-00Knob : Gray (inner p.b. - slope)
    1-3366-1280-00Knob : Gray (outer - level)
    1-22 (R75,R175)311-0326-00Res.,Var,Nonwir,10K ohm, 20%, 0.50W (A-B W7683 - preset)
    1-10 (R70/S70,R170/S170)311-1715-00Res.,Var,Nonwir : 10K ohm,20%,1W w/Switch (A-B 13M865A - Level/Slope)
    1-6260-1650-00Switch, Rotary : Thumbwheel (Digitran 23-T-1 5 digits frequency)