547

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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
Line voltage 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
Sweep Rates 100 ns/div to 5 s/div
Trigger Coupling AC, DC, AC LF Rej
External Horizontal Input 100 mV/cm to 10 V/cm, DC to 400 kHz
CRT T5470, 10 kV acceleration, 6x10 cm viewing area
Calibrator ~1 kHz, 200 μ Vp-p to 100 Vp-p
Power consumption 510 W
Cooling 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.

CRT

The 547 uses the Tektronix 154-0478-00 CRT unless optioned for a special phosphor.

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. However, this this reduces the load on the regulator circuit by about 1 Watt due to the lack of tube heater filaments. This forces the regulator past its design limit and can 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.

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, +350 V, as well as a +325 V unregulated output for CRT HV section.

Multiple secondary windings feeds 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. 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. Heater voltage is applied to all tubes immediately when the power switch is turned on.

Links

Common Problems

Pictures

547

547 Internals

RM 547

Schematics


Some Parts Used in the 547

Page Class Description Used in
12AT7 Vacuum Tube (Dual Triode) dual high-gain triode 161 180 310 310A 315 316 360 502 502A 512 513 513D 514 514AD 514D 516 524AD 529 RM529 544 546 547 556 3A2 3A75 1M1 A B C G H K L M N K R S Z
12AU7 Vacuum Tube (Dual Triode) dual medium-μ triode 122 160 161 162 181 190 310 316 317 502 502A 512 516 517 517A 526 535 536 545 545A 545B 547 549 555 575 581 581A 585 585A C D E N Q
12AX7 Vacuum Tube (Dual Triode) dual triode 513 531 531A 535 536 545 545A 545B 546 547 549 555 581 581A 585 585A E Q
12B4 Vacuum Tube (Triode) power triode 126 310 310A 316 317 502 502A 526 541 541A 535 535A 545 545A 546 547 549 551 555 513 581 581A 585 585A
5642 Vacuum Tube (Diode) directly-heated high-voltage rectifier 310 310A 316 317 360 453 502 502A 503 504 506 513 515 516 529 RM529 533 533A 535 536 543 543A 543B 545 545A 545B 547 551 555 556 567 575 581 581A 585 585A 647
6080 Vacuum Tube (Dual Triode) dual power triode 132 160 316 317 535 535A RM35A 541 541A 535 536 545 545A 545B 546 547 549 575 581 581A 585 585A
6AU6 Vacuum Tube (Pentode) RF pentode 2A60 80 107 160 181 190 310 310A 316 317 360 502 502A 512 513 516 517 517A 526 529 RM529 531 531A 535 536 545 545A 546 547 549 555 575 581 581A 585 585A C CA Q
6CW5 Vacuum Tube (Pentode) power pentode 132 526 547
6DJ8 Vacuum Tube (Dual Triode) dual triode 80 132 161 310A 316 317 3A75 502 502A 503 504 515 516 519 526 529 RM529 533 535 536 543 544 545 545A 545B 546 547 549 555 556 565 581 581A 585 585A 661 2A60 63 2A63 3A7 3A8 1121 1A4 67 81 82 86 3B1 3B4 1S1 B O W Z Telequipment S32A Telequipment D52 Telequipment TD51 Telequipment S52 Telequipment S51 Telequipment Type A
T5470 CRT 5" electrostatic deflection CRT 543B 544 545B 546 547