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Tektronix TU-4
560 Series test load plug-in
Tektronix TU-4

Compatible with 560-series scopes

Produced from 1961 to March 1963

(All manuals in PDF format unless noted otherwise)
Manuals – Specifications – Links – Pictures

The Tektronix TU-4 is a plug-in for testing 560-series oscilloscope mainframes including the Type 506 as well as the Type 129 four bay plugin enclosure and power supply. It contains load resistors for testing the power supplies of the scope. These apply lighter loads to the early 560, low power scopes, and heavier loads to the later 561 and other higher power scopes in the 560 family. For full load testing, two TU-4 units are necessary, and, presumably four for a Type 129.

There are two neon lamps on the TU-4 front panel that are intended to show whether the AC line input power of the scope under test is connected correctly. The functioning of these lamps depends on 117 VAC hot and neutral being connected to pins 7 & 8, respectively, in the plugin connectors of the scope being tested. This will work correctly even if the scope being tested is wired for 234 VAC. These pins were not connected in later models of the 560 series. Consequently, the neon lamps are non-functional when the TU-4 is used with a 561B, a 564B, or a 568 (SN 288 or later.)

When the TU-4 is properly calibrated, the RIPPLE AND PERCENT DC ERROR connector output delivers 10 mV for each 1% error of the the power supply in the scope. This output has a 1 MΩ source impedance and is designed to drive a 1 MΩ scope input. Thus, monitoring this voltage using a modern DVM will exaggerate any error by a factor of about 1.8. There is a button to filter the ripple from this output, and another button to ground the output, to provide an accurate ground reference. While development of the TU-4 was stopped rather early, due to the difficulty of getting it to work correctly with all the members of the 560 family, it remains useful for doing quick checks of voltage and ripple.

The SIGNAL INPUT connector drives the vertical deflection plates directly, with no amplification. Connecting a 20 V calibrator signal to this input should produce a square wave about 2 cm high. Moving the toggle switch to the DUAL TRACE position should produce two traces about two major divisions apart. If this calibrator signal is also connected to the Z AXIS INPUT, this should reduce the intensity of the leading edge(s) of the square wave(s).

Note that some of the photos on this page show a TU-4 with BNC connectors instead of UHF connectors. That change was scheduled to start at SN 300, but production ended before this upgrade could be implemented. The UHF connectors, but not the binding post, were scheduled to be changed. One of the small black knobs on this upgraded unit is also incorrect; all three small knobs should be the same. While the BNC connectors are a welcome improvement, the TU-4 with BNCs shown on this page must have been upgraded after it was sold.



Some Parts Used in the TU-4

Part Part Number(s) Class Description Used in
0G3 154-0291-00 Gas Discharge Tube (Voltage regulator) 85 V voltage reference 132 506 547 560 561 561A 561S 564 565 567 661 TU-4 Z
6BJ8 154-0305-00 Vacuum Tube (Triode) medium-μ triode + dual diode TU-4 51
6DJ8 154-0187-00 154-0305-00 Vacuum Tube (Dual Triode) dual triode 132 161 310A 316 317 502 502A 503 504 506 515 516 519 526 529 RM529 533 535 536 543 544 545 545A 545B 546 547 549 555 556 561A 561S 564 565 567 581 581A 585 585A 661 1A4 1S1 60 2A60 63 2A63 67 2B67 3A1 3A1S 3A2 3A3 3A6 3A7 72 3A72 75 3A75 4S2 51 3B1 3B1S 3B2 3B3 3B4 3M1 3S76 3T77 3T77A 9A1 9A2 1121 80 81 82 86 B O W Z Telequipment S32A Telequipment D52 S-311 Telequipment TD51 Telequipment S52 Telequipment S51 Telequipment Type A TU-4
NE-2 150-002 150-0002-00 Gas Discharge Tube (Neon lamp) Neon lamp 511 511A 581 581A 585 585A 545A TU-4