547

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Tektronix 547
50 MHz oscilloscope
Tektronix 547 with 1A1 plugin, in ALT Delayed Trigger

Produced from 1964 to 1975

Manuals
Manuals – Specifications – Links – Pictures

The Tektronix 547 is a 50 MHz scope that takes letter-series and 1-series plug-ins.

It has two identical timebases and, when used with the 1A1, 1A2, or 1A4, has the ability to display one input with one time scale and another input with a different time scale. The effect is similar to a dual-beam scope assuming that the input signals are repetitive. This "Sweep Switching" feature differentiates the 547 from the 546.

There is also a rackmount version, the RM547 or R547.

The program manager for the development of the Tektronix 544, 546, and 547 was Bob Rullman. The 547 vertical amplifier was designed by Keith Taylor.

Key Specifications

Bandwidth DC to 50 MHz (−3 dB) with fast plug-ins (1A1, 1A2, 1A4, 1A5)
Rise time 7 ns with 1A1
Sweep Rates 100 ns/div to 5 s/div
External Horizontal Input 100 mV/cm to 10 V/cm, DC to 400 kHz
CRT T5470 (154-0478-00 standard), 10 kV acceleration, 6x10 cm viewing area
Calibrator ~1 kHz, 200 μVp-p to 100 Vp-p
Power 90-136 V or 180-272 V, selected via primary voltage selector (inside cabinet) and voltage range selector (on rear panel), 50/60/400 Hz, 510 W, AC Fan

Internals

Triggering

The 'A' and 'B' triggers are based on a 10 mA tunnel diode. Up to serial number 11889, it uses a TD253. From 11890 onward, it uses a 152-0140-01.

HV Transformer

A common problem with 547s is the HV transformer. Rather than potting the HV transformer in wax, as was done up to that point, the 547's HV transformer was potted in epoxy. Unfortunately, this epoxy turned out to absorb moisture over time, particularly when used in humid climates. The moisture causes increased losses in the transformer.

Excessive losses require the regulator to drive the 6AU5 input oscillator tube (V800) harder. Eventually, the drive circuit cannot supply enough power to keep the supply in regulation. The usual solution is to scavenge a replacement transformer from another scope. As a labor of love, hobbyists have been known to rebuild the HV transformers. This is discussed from time to time on the groups.io (formerly Yahoo) TekScopes forum.

Bernie Schroder has found that the HV transformer degeneration can be slowed considerably by keeping the HV module cool and dry. The mod he was taught by Jim Willams involves replacing the 5642 tube rectifiers with NTE517 diodes to reduce the load on the regulator circuit by about 1 Watt by eliminating the filaments. However, this can force the regulator past its design limit and result in lack of regulation, until the transformer heats up and more power is required due to losses.

After changing to semiconductor diodes, it will be seen that grid pin 7 of V814 will be about 0 volts (fully on, with no swing to regulate) in an attempt to force its anode (pin 6) to about +55 V, which is the screen input of the 6AU5 (pin 8).

One way to remedy this is to replace the anode resistor coming off pin 6 of V814 (R803) from 56 kΩ to 82 kΩ. Doing so changes the grid voltage on pin 7 of V814 to a comfortable −0.8 V at switch-on.

Again, this becomes more negative as the losses inside the transformer increase, but not by much if the transformer is healthy.

A second path to thermal runaway on early serial numbers is C808, which resonates the transformer primary winding. Tek used a Sprague 160P DiFilm Black Beauty. In the 2020's, 160P's are exhibiting high Dissipation Factor when warm, enough to self-heat in this case. Replace with any modern capacitor.

Vertical Amplifier

The 547 has a five-stage BJT vertical amplifier that is fully differential from the plug-in connector to the CRT vertical deflection plates. There is one tube in the vertical signal path, a 12AT7 acting as a unity-gain buffer between the plug-in connector and the vertical amplifier.

Spoiler Switch

The plug-in bay of the 547 has a "spoiler switch" that only enables the full bandwidth of the 547's vertical signal path when certain relatively modern plug-ins are used, such as the 1A1, 1A2, 1A4, and 1A5.

Those plug-ins have a small hole to the left of the plug-in to mainframe connector, so they can be fully inserted without pressing the spoiler switch. (Spectrum analyzer plug-in Types 1L30 and 1L40 have the hole too but for no reason since their vertical output is low frequency.)

Delay Line

There is a 170 nanosecond delay line between the first and second gain stages.

Power Supply

The 547's power supply provides regulated outputs of −150 V, +100 V, +225 V, and +350 V, plus a +325 V unregulated output for the CRT HV oscillator.

Multiple secondary windings feed diodes for rectification for different voltages, using both center-tap and bridge configurations. The regulator section uses no transistors, only tubes. There are multiple 6.3 V secondary outputs for heaters, some elevated to different voltage levels based on the section/tube that is supplied, in order to keep the heater-to-cathode voltage level within limits.

As is common in many Tektronix scopes, all regulated voltages are referred to the negative regulated rail (−150 V in this case) by fixed low-tolerance dividers. Only the −150 V voltage is trimmed; its reference is a OG3 VR tube. A 12AX7 is used as the comparator and two 6CW5 in parallel are used as series pass tubes. A 6AU6 is used as an error amplifier. Most other power supply sections in the 547 replicate the same basic design, except slight changes in tubes used: The +225 V and +100 V regulators employ a 6080 as the pass element, and +350 uses a 6CW5.

The plate voltage delay circuit is similar to that found in many may other Tek scopes of the same era. Heater voltage is applied to all tubes immediately when the power switch is turned on. A 6N030T delay tube (P/N 148-0021-00) controls a relay that switches plate supply voltages on only after the tubes are warmed up.

Links

Common Problems

Pictures

547

547 Internals

RM 547

Schematics

Components

Some Parts Used in the 547

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
120-0308-00 120-0308-00 Discrete component high voltage transformer 543B 544 545B 546 547
12AT7 154-0039-00 Vacuum Tube (Dual Triode) dual high-gain triode 161 180 310 310A 315 316 360 502 502A 511A 512 513 513D 514 514AD 514D 516 524 529 RM529 544 546 547 556 565 570 3A2 75 3A75 1M1 A B C G H K L ML M N K R S Z
12AU6 154-0040-00 Vacuum Tube (Pentode) RF pentode 81 112 1L10 1L20 1L60 3L10 512 556 575 545 547 549 581 585 A B C G K H L ML M N O R S Z
12AU7 154-041 154-0041-00 154-0287-00 Vacuum Tube (Dual Triode) dual medium-μ triode 104 104A 122 160 161 162 181 190 310 310A 316 317 3C66 502 502A 507 511A 512 516 517 517A 524 526 535 536 545 545A 545B 547 549 555 561 564 570 575 581 581A 585 585A C D E N Q Hickok 1825
12AX7 154-043 154-0043-00 Vacuum Tube (Dual Triode) dual triode 3C66 513 524 531 531A 535 536 545 545A 545B 546 547 549 555 570 581 581A 585 585A E Q Hickok 1825
12B4 154-044 154-0044-00 Vacuum Tube (Triode) power triode 126 310 310A 316 317 502 502A 524 526 541 541A 535 535A 545 545A 546 547 570 549 551 555 513 581 581A 585 585A
1N3714 152-0081-00 Discrete component 2.2 mA, 25 pF germanium tunnel diode 546 547 556 21A 22A 3B1 3B2 3B3 422 491 283
1N3717 152-0381-00 152-0125-00 Discrete component 4.7 mA, 25 pF tunnel diode 1L40 1S1 1S2 11B1 11B2 11B2A 147A 1470 148 21A 22A 3B4 3B5 408 432 434 453 453A 454 466 491 5T3 544 RM544 546 RM546 547 RM547 556 RM556 7B70 7B71 7D11
2N2207 151-063 151-0063-00 Discrete component germanium PNP transistor 3B1 3B3 3S76 321A 547
5642 154-0051-00 154-0079-00 Vacuum Tube (Diode) directly-heated high-voltage rectifier 310 310A 316 317 360 453 502 502A 503 504 506 513 515 516 524 529 RM529 533 533A 535 536 543 543A 543B 545 545A 545B 547 551 555 556 560 561 561A 561S 564 567 570 575 581 581A 585 585A 647 647A
6080 154-0056-00 154-0315-00 Vacuum Tube (Dual Triode) dual power triode 132 160 316 317 516 535 535A RM35A 541 541A 535 536 545 545A 545B 546 547 549 565 567 575 581 581A 585 585A
6197 154-0146-00 Vacuum Tube (Pentode) 7.5 W power pentode 516 531 533 535 535A 547 556 75 3A75
6AU5 154-021 154-0021-00 Vacuum Tube (Pentode) 10 W beam power pentode 507 513 516 517 517A 531 535 541 535 545 547 581 581A 585 585A
6AU6 154-0022-00 157-0073-00 157-0059-00 154-0284-00 Vacuum Tube (Pentode) RF pentode 107 160 181 190 60 2A60 72 3A72 3C66 310 310A 316 317 360 502 502A 506 511 511A 512 513 516 517 517A 524 526 529 RM529 531 531A 535 536 545 545A 546 547 549 555 561 561A 561S 564 565 567 570 575 581 581A 585 585A 80 C CA Q
6BY8 154-0414-00 Vacuum Tube (Pentode) diode-pentode 547
6CW5 154-0202-00 Vacuum Tube (Pentode) power pentode 132 526 547 General Radio 1124 Telequipment D56
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 D56 Telequipment S32A Telequipment D52 S-311 Telequipment TD51 Telequipment S52 Telequipment S51 Telequipment Type A TU-4
8426 Vacuum Tube (Pentode) RF pentode O 545A 547 549 581A 585A
SMTD995 152-0140-01 Discrete component 10 mA, 8 pF tunnel diode 1S1 1S2 1502 21A 22A 3T5 3T6 475 475A 475M 544 R544 546 RM546 547 RM547 556 R556 581A 585A RM585 7B52 7B53N 7B70 7B71 7D10 7D11 7T11 7T11A R7912 S-51 S-52 TU-5 067-0572-00 067-0572-01 067-0681-00
STD704 152-0125-00 Discrete component 4.7 mA tunnel diode 1L40 1S1 11B1 11B2 11B2A 147 R147 147A R147A 1470 148 R148 148-M 149 R149 149A R149A 21A 22A 3B4 3B5 408 432 434 453 453A 454 464 465 466 491 5T3 544 RM544 546 RM546 547 RM547 556 RM556 7B70 7B71 7D11
T5470 154-0429-00 154-0450-00 154-0451-00 154-0452-00 154-0457-00 154-0458-00 154-0459-00 154-0478-00 154-0478-01 154-0478-02 154-0478-03 154-0568-00 154-0568-01 154-0568-02 154-0568-03 CRT 5" electrostatic deflection CRT 543B 544 545B 546 547
TD202 152-0155-00 Discrete component 2.2 mA, 25 pF tunnel diode 546 RM546 547 RM547
TD253 152-0154-00 Discrete component 10 mA, 9 pF germanium tunnel diode 547 7B70
TD714 152-0402-00 Discrete component 2.2 mA, 25 pF tunnel diode 1401 1401A 283 R283 3B2 3B3 422 491 546 RM546 547 RM547 556 RM556 SPG11 SPG12