549

Manuals – Specifications – Links – Pictures

The Tektronix 549 is the only storage scope in the 500 series (except for the 537 that never left prototype stage).

It takes a letter-series or 1-series vertical plug-in. The 549 was introduced in 1965 and discontinued after 1973.

Mel Holznagel designed the vertical output stage. Bob Shand did the mechanical design.

Key Specifications

Bandwidth	DC to 30 MHz (−3 dB) with fast plug-ins (1A1, 1A2, 1A4, 1A5)
Rise time	12 ns
Writing speed	5 cm/μs
Power	104/115/127 or 208/230/254 VAC ±10%, primary voltage selector (inside cabinet) + voltage range selector (on rear panel), 50 to 60 Hz, 650 W/750 VA
Thermal protection	65°C (150°F) Automatic resetting thermal cutoff
Size	43.2 cm × 32.9 cm × 60.7 cm (W/L/H, 13" × 24" × 17")
Weight	31 kg (68 lb)
Cooling	AC Fan
Accessories	012-0102-00 remote control cable/switch

Links

• Rajesh's Tek 549 Restoration / Video
• Tektronix, the Storage Story (1966) @ radiomuseum.org
• A 549 @ YouTube
• Deon's 549 with 564 HT Transformer

Documents Referencing 549

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Patents that may apply to 549

Page	Title	Inventors	Filing date	Grant date	Links
Patent US 3426237A	Automatic erase circuit for storage tube	Don Calnon • Russ Fillinger • Melvin A. Holznagel • Richard W Stack	1965-08-23	1969-02-04	549 • Direct-view storage CRT

Internals

Mix of Transistors and Tubes

Like many Tek scopes from the period, the 549 uses a mix of transistors and tubes. For example, consider the buffer amplifier in the 549, whose purpose is to interface the high-impedance output of the plug-in with the low-impedance of the 200 ns delay line in the 549. As is usual in oscilloscope vertical circuits, the requirement is to have flat frequency response from DC to the maximum frequency of the scope and to have linear phase response over this same frequency range.

In the 549, this buffer is implemented with a 6DJ8 cathode follower at the plug-in interface driving an NPN BJT differential amplifier at the bottom of a cascode with a 7119 tube on top. The output of the cascode (the plate of the 7119) drives the delay line.

Since the entire signal path is differential, the common-mode voltage does not have to be zero, and it is not – the differential signal in the delay line rides on 167 volts of DC.

After the delay line, the signal enters another cascoded differential amplifier with NPN BJTs on the bottom and a pair of 10-watt 8608 power pentodes on the top whose plates drive the CRT's vertical deflection plates of the CRT through inductive matching/peaking networks.

Non-Distributed Amplifier

The 549 is slightly unusual among 54x-series scopes in that it does not use a distributed vertical amplifier. (Other exceptions include the 545B and 547).

Triggering

Triggering is done using an NPN BJT Schmitt trigger.

Storage

The 549 uses the T5490 CRT which has two storage targets, upper and lower, whose storage mode and erase signals can be controlled independently.

The 012-0102-00 remote control cable/switch (also used for 564B) can be used to remotely erase the screen and reset the single sweep. It connects to an Amphenol 165-16 socket at the rear top of the scope (see 549 remote control connector for pin-out).

Power Supply

The 549's power supply provides regulated outputs of −12.4 V, −150 V, +100 V, +225 V, +300 V, +350 V, and +500 V as well as a +475 V unregulated output.

Line input is connected to main transformer primary via two switches, one inside the chassis to select the 110 V or 230 V range, and another on the rear of the chassis to select Low/Medium/High voltage in either range.

Multiple secondary windings feeds diodes for rectification for different voltages. Both center-tap and bridge configuration is used. Transistors and/or tubes are used for regulation.

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 5651 VR tube. A 12AX7 is used as the comparator, three 12B4 in parallel are used as series pass tubes. A 6AU6 is used as an error amplifier.

Most other stages replicate the same design, except slight changes in tubes used − the +350 V, +225 V and +100 V regulators employ a 6080 as the pass element.

The −12.4 V regulator is transistor-based.

The 549 power supply uses a 6N030 delay relay (P/N 148-0021-00) to control a relay that switches supply voltages on only after the tubes are warmed up. On power up, only heater voltage is applied to the tubes. After a delay of up to 60 seconds, the thermal delay relay activates the main relay (driven from unregulated +170 V). This also cuts out the delay relay, which can cool down and will be ready to delay again even after a quick interrupt in power input.

The 549 has a 65°C (150°F) thermal cutoff.

The 549 uses a 120-0423-00 HV transformer driven by a 6GF5 tube from +470 V.

HV Transformer Problem and Replacement

The HV transformer (part #120-0423-00) uses epoxy impregnation like models 544,545B,546,547,556 and as such suffers the same issue of increasing losses with age unlike the earlier bee's wax transformers. This issue will eventually lead to failure of the HV oscillator circuit resulting in loss of display intensity, blooming and finally vanishing trace. One solution is to use a donor HV transformer out of a 564 storage scope. This was successfully implemented by Morris Odell and Deon Vandenberg however invented by another. A photo is provided below showing the new transformer installed with terminals arbitrarily labelled to help others perform the same task. Looking at the photo the top connections are obvious. The left middle connection goes to the right strip pin 9 (labelled as 9) The bottom section has two connections, one on the left towards the neons(labelled A) this goes to the anode of the driver tube V800 pin 7. The other obscured wire is the bottom left which goes to the 4th pin on the left strip (labelled as 4). Resistor R807 is to be changed from 39k to 47k. Resistor R2 is to be added between the junction of D836 and C842 and R837. (See schematic.) When this is done adjust the HT at the test point to -3700V (R855) and adjust R815 to make the grid voltage -3790V (located at test point labelled TP). To see the new transformer in action click on the bottom youtube link.

Pictures

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  549 front, earlier round bezel

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  549 front, later rectangular bezel

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  549 Storage controls

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  Front of a 549

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  549 Rear

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  Line voltage selector

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  B INTEN BY A Trig in 549

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  Dual trace display in 549

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  549 knob layout

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  549 ad in Electronics 1965-08-23

Internal

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  LHS

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  RHS

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  RHS Timebase Ch: Door Open

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  Top

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  Underside

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  8608 vertical output tubes

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  Vertical amp

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  8608 vertical output tubes

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  8608 vertical output tubes

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  Top view

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  Storage board

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  Power supply behind door

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  Right side internal

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  Primary voltage range selector

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  LV power supply tubes

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  LV power supply tubes

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  Storage board Rev "PC" (recapped)

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  Storage board Rev "PE"

HT Transformer modification

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  564 HV transformer installed in the 549

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  Schematic showing other changes required