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.
|Bandwidth||DC to 50 MHz (−3 dB) with fast plug-ins (1A1, 1A2)|
|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|
The 547 uses the Tektronix 154-0478-00 CRT.
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 tube rectifiers with NTE517 diodes. This removes the tube filament heat and current load. Adjust grid of driver tube as required for appropriate regulation range (see photo below)
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.
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, 1L30, and 1L40. 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.
- Spoiler switch explanation excerpted from Tek 547 544 546 Technical Instruction and Training (PDF)
- Spoiler switch explanation excerpted from Tek 547 Notes (PDF)
There is a 170 nanosecond delay line between the first and second gain stages.
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. Both center-tap and bridge configuration is used. Its a all Tube design for the regulation. There are multiple 6.3V secondary outputs for heaters, many elevated to different voltage levels based on the section/tube its used for to keep the Heater-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, +350 uses a 6CW5.
The plate voltage delay circuit is similar to that found in many may other Teks of the same era. A 6N030 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.
- 547 Restoration with video
- Tek 547 in "Reading Jim Williams" blog: Scope Sunday 13 and Vintage Scopes are Better, pt.1
- "MightyOhm" blog: Jim Williams workbench
- Comparing an Apollo Era Workhorse to Today’s Bench Scope @ tek.com
- Eiki Martinson: Tektronix 547 Oscilloscope—Getting an Old Soldier Back in the Fight
- Tek 547 page @ amplifier.cd
- The Tektronix 547 Oscilloscope - Magic in the Box
- J.Evans's 547 page
- See 547/Repairs
547 with 1A1
Tek 547 HV Section and 5642HV Rectifier Tube (Cover removed)