511

The 511 was Tektronix' first oscilloscope, introduced in June 1947 but only the second product released by the young company – the first was the Type 101 Video Calibrator. Howard Vollum was directly involved with the design of the 511.

According to TekWeek March 23, 1984, "511" stood for 5-inch tube, 1 channel, 1st model. It sold for $795^{[Note 1]}, compared to $1,800 for a two-piece Dumont scope that was mostly pre-war technology.

An improved version, the 511A, was introduced in November 1948. Major improvements included a regulated power supply for CRT, and a (in later models, s.b.) a calibrator. The 511AD was available through 1953.

Key Specifications

Bandwidth	5 Hz to 10 MHz (8 MHz with 2-stage amplifier); no DC coupling
Rise time	40 ns (50 ns with 2-stage amplifier)
Deflection	Without amplifier, 27 V/cm – 200 V/cm, DC or ACp-p. 1-stage amplifier, 2.7 V/cm – 40 V/cm. 2-stage amplifier, 0.27 V/cm – 4 V/cm.
Input	1 MΩ // 40 pF; 600 V max. DC+peak AC
Sweep	100 ns/cm to 10 ms/cm + variable; ×5 magnifier
Trigger	0.5 to 50 V (Peak) sine or pulse ≥50 ns
X input	DC coupled via 100 K potentiometer and sweep amplifier; 1.5 V/cm or less; DC to 800 kHz
CRT	5CP, 3 kV acceleration
Calibrator	Clipped sine wave of power line frequency, ranges 0-0.3, 0-1, 0-3, 0-10, 0-30, 0-100 Vp-p
Outputs	Sweep sawtooth, 20 Vp-p; Positive and negative gate, 40 Vp-p
Weight	511 – 29 kg (65 lb); 511A – 23 kg (50 lb);
Dimensions	15½" high, 12½" wide, 21½" deep
Power	511 – 180 W; 511A – 105-125 or 210-250 V, 50-60 Hz, 230 W

(511A unless noted otherwise)

There is also a 511AD, where the "D" in the model number indicates that it has an L-C delay line.

Prices

• $795 in 1948 (~$9,700 in 2023 dollars)

Internals

The 511/511A uses a standard CRT, the 5CP1A (with P1 phosphor), 5CP7A (P7) or 5CP11A (P11) below S/N 5100, the 5ABP from 5100 up. P1 was standard, P7 and P11 optional at no extra charge.

The vertical output is a pair of 6AG7 tubes, AC-coupled to the vertical deflection plates. The horizontal amplifier is DC-coupled through a chain of five NE-2 neons on either side for voltage offset.

There was an option that added a 1 μs marker generator.

Neither the 511 nor the 511A has a thermal cutoff.

511

The original 511 was produced with serial numbers 101 to 454 (June 1947 – November 1948).

There are two power transformers, T1 and T2, both operating on 60 Hz mains power with their primaries in parallel. T1 produces the CRT anode and cathode voltages, as well as various other regulated and unregulated voltages. The CRT cathode and anode voltages (+1500/-1500 V) are simply rectified voltages from the secondary of T1. The lack of regulation means that variations in mains voltage results in variation of deflection sensitivity. The +275 V and + 475V rectifier circuits have choke inputs.

511A (SN 455+)

The main difference introduced in the 511A is the power supply. The regulated positive supply voltages were lowered somewhat to +225 V and +450 V, with capacitor-input circuits (no chokes).

The CRT cathode and anode voltages are produced by a 2 kHz oscillator (a 6AQ5) that is powered by the +225 V_DC regulated supply. This results in vertical deflection calibration that is independent of mains voltage. HV rectifiers are two 1B3GT tubes producing +1500/-1500 V.

511A (SN 1406+)

Beginning with SN 1406, the 511A(D) gained a continuously variable sweep speed control, visible as a 2nd dial next to the "sweep speed multiplier".

511A (SN 2406+)

From SN 2406 upward, a dedicated calibrator stage uses one half of a 12AT7, V16.1, to clip a voltage derived from the mains transformer to a 100 V level divided from the regulated +225 V rail.

The HV rectifier uses two 1V2 tubes producing +1800/-1500 V.

Delay

The Tektronix Type 1-AD-25 delay line, composed of 24 L-C sections, was available as a factory option for the 511A. With the delay, the scope is a 511-AD. Even when ordered without the delay, the 511's chassis was pre-drilled for the delay so that it could be added later, in the field, without drilling. The delay could be switched in and out of the signal path, presumably to avoid the slight signal degradation the delay causes.

History

The 511 was designed by Frank Hood, Logan Belleville, and Howard Vollum.

• See also https://vintagetek.org/tektronix-first-products/

Tektronix engineer Frank Hood recollects:

My first assignment was to build or modify some special instruments for Bonneville Power. They wanted a device that would detect and record any lightning strikes or arc-overs on the high voltage power lines running between Vancouver, Wash. and other cities such as Longview, Spokane, etc. They wanted to detect each event, in a fraction of a millionth of a second, then to send a pulse of energy down the defective line and measure the time it took to return, (this was an application much like radar). They wanted markers displayed at each mile and fraction of a mile so that they could determine the exact location of the fault. They needed to record a photographic image for latter study. Two or more such instruments were built. We called these Type 511B. They worked very well and were used for several years.

John Addis says:

The 511 was indeed somewhat crude. The vaunted calibrator which Vollum introduced to give people the sense that you could make real measurements is actually just a 60 Hz sine wave off the power transformer, not even a square wave, so it is completely unregulated. Fortunately for Vollum, both the calibrator and the CRT HV are unregulated. When the line voltage goes down, the scope sensitivity goes up (reduced HV makes beam converge less after plates). So the displayed calibrator amplitude is not very sensitive to line voltage.

Links

• Richard Sears' detailed 511A Page
• [Note 1] TekWeek March 23, 1984 says $595 but the advertised price was $795 (see below).

Pictures

511

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  511 sn305 Front

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  511 sn305 Top

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  511 sn305 Bottom

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  511 sn305 Back

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  511 sn305 Sweep chassis

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  511 sn305 Power Supply, Video Amplifier

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  511 sn305 HV shroud

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  Vollum scope - Electronics Magazine, April 1948

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  511 ad from September 1948

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  511 non-A power supply schematics

511A

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  511A

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  511A

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  511A

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  511A ad from Electronics Magazine, November 1948, p.239

511AD

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  511AD

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  511AD

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  511AD

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  511AD

Components

Some Parts Used in the 511

Part	Part Number(s)	Class	Description	Used in
0C3	154-0002-00	Gas Discharge Tube (Voltage regulator)	105 V voltage reference	511
0D3	154-003 • 154-0003-00	Gas Discharge Tube (Voltage regulator)	153 V voltage reference	511 • 511A • 513 • 514
2X2	154-0085-00	Vacuum Tube (Dual Rectifier)	dual rectifier	511
5CP	154-062 • 154-0062-00	CRT	5" CRT with post-deflection acceleration	511 • 511A
5U4	154-086 • 154-0086-00	Vacuum Tube (Dual Rectifier)	dual rectifier	511
6AC7	154-011 • 154-0011-00	Vacuum Tube (Pentode)	RF pentode	511 • 511A
6AG7	154-012 • 154-0012-00	Vacuum Tube (Pentode)	9 Watt power pentode	104 • 104A • 105 • 112 • 511 • 511A • 512 • 513 • 514 • 517 • 517A • 524
6AL5	154-016 • 154-0016-00 • 154-0038-00	Vacuum Tube (Dual Diode)	high-perveance dual diode	163 • 181 • 190 • 1M1 • 310 • 310A • 315 • 316 • 317 • 3B1 • 3B1S • 3B2 • 3B3 • 3B5 • 502 • 502A • 503 • 511 • 511A • 512 • 516 • 517 • 517A • 524 • 526 • 535 • 535A • 545 • 545A • 549 • 551 • 565 • 570 • 581 • 581A • 585 • 585A • C • T • Telequipment D52 • Telequipment D56 • Telequipment S52
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
6C4	154-029 • 154-0029-00	Vacuum Tube (Triode)	VHF triode	190 • 3B2 • 507 • 511 • 511A • 517 • 517A • Chemtrix 205
6J6	154-032 • 154-0032-00	Vacuum Tube (Dual Triode)	high-frequency dual triode	104 • 104A • 161 • 511 • 511A • 512 • 517 • 517A
6L6	154-087 • 154-0087-00	Vacuum Tube (Pentode)	beam power pentode	511
6SJ7	154-088 • 154-0088-00	Vacuum Tube (Pentode)	Pentode	511
6V6	154-089 • 154-0089-00	Vacuum Tube (Pentode)	12-watt beam power pentode	511
6X5	154-090 • 154-0090-00	Vacuum Tube (Dual Rectifier)	dual rectifier	511
NE-2	150-002 • 150-0002-00	Gas Discharge Tube (neon lamp)	Neon lamp	511 • 511A • 581 • 581A • 585 • 585A • 545A • TU-4