7904
The Tektronix 7904 is a 500 MHz, non-storage 7000-series oscilloscope mainframe with four bays. It accepts two 7000-series vertical plug-ins and two 7000-series horizontal plug-ins. There is also a rack-mount version, the R7903, albeit with only one horizontal bay.
The 7904 was introduced in late 1971/early 1972 (Note 1). In 1984, it was replaced by the redesigned 7904A.
Performance is largely determined by the plug-ins. The 7A19 vertical amplifier and 7B92 time base were introduced along with the 7904 to match the 500 MHz system bandwidth.
Design Staff of 7904 Project (from July 1971 Tekscope):
Val Garuts was project manager and developed the large signal amplifier circuit used in the horizontal and Z-axis amplifiers. Thor Hallen did the 7A19 plug-in and the vertical amplifier, and John McCormick the horizontal. The trigger and time base (7B92 plug-in) were done by Les Larson and Bill DeVey. Bill Peek worked on the Z-axis amplifier and auto-focus, with Hans Springer doing the mainframe interface and channel switching. Joe Burger's work on the power supply, coupled with Joel Swanno’s efforts in mechanical design, reduced the weight to only 30 pounds. Ken Hawken did the fine job on the CRT.
Key Specifications
| Bandwidth | 500 MHz (with 7A19 or 7A29 amplifier) |
|---|---|
| Fastest calibrated sweep | 500 ps/Div (with 7B92A, other time bases "uncalibrated for first 60 ns") |
| Outputs | Vertical Signal Out (25 mV/Div into 50 Ω, 0.5 V/Div into 1 MΩ); +Sawtooth; +Gate; camera power; probe power |
| Inputs | Z Axis (15 Vp-p) |
| CRT |
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| Calibrator | DC, square wave (1 kHz or ½ B Sweep gate), 4 mV to 40 V in decade steps (2/20/200/400 mV into 50 Ω); 40 mA current loop |
| Power | 90−132 V or 180−264 V, 48−440 Hz, 190 W max. |
| Weight | 13.5 kg (30 lbs) |
| Dimensions | 34.2 cm × 30.5 cm × 69.5 cm (13.5 in x 12.0 in x 23.8 in) H×W×L |
| Options |
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Links
- 7904 Repair with Video
- Tek 7904 @ amplifier.cd
- Repairing front panel buttons of Tektronix 7904 oscilloscope
Documents Referencing 7904
| Document | Class | Title | Authors | Year | Links |
|---|---|---|---|---|---|
| Tekscope 1971 V3 N4 Jul 1971.pdf | Article | A Subnanosecond Realtime Oscilloscope | Val Garuts • Thor Hallen | 1971 | 7904 • 154-0644-00 • 7A19 • Ft doubler • 7B92 |
| 7000 series brochure March 1973.pdf | Brochure | 7000 series brochure, March 1973 | 1973 | 7A11 • 7A12 • 7A13 • 7A14 • 7A15A • 7A16A • 7A17 • 7A18 • 7A19 • 7A21N • 7A22 • 7B50 • 7B53A • 7B70 • 7B71 • 7B92 • 7CT1N • 7D11 • 7D13 • 7D14 • 7D15 • 7M11 • 7L12 • 7S11 • 7S12 • 7T11 • 7704A • R7704 • 7904 • R7903 • 7603 • R7603 • 7403N • R7403N • 7313 • R7313 • 7613 • R7613 • 7623 • R7623 • P7001 | |
| Tekscope 1974 V6 N3.pdf | Article | Servicing the 7904 high-efficiency power supply | 1974 | 7904 |
Patents that may apply to 7904
| Page | Title | Inventors | Filing date | Grant date | Links |
|---|---|---|---|---|---|
| Patent US 3453403A | Power selection device | Eldon Hoffman | 1966-08-18 | 1969-07-01 | 115 • 140 • 141 • 141A • 144 • 145 • 146 • 147 • 148 • 149 • 149A • 230 • 284 • 286 • 453 • 454 • 491 • 520A • 521A • 522 • 545B • 547 • 556 • 561B • 564B • 568 • 576 • 611 • 647A • 2101 • 2601 • 5030 • R5030 • 5031 • R5031 • 7503 • 7504 • 7704 • 7704A • 7904 • R7903 |
Operation
The 7904 has many modes of operation. One mode is called "Independent-Pairs Display" in the manual, where the input to the left vertical plug-in is displayed using the B horizontal time-base plug-in, and the input to the right vertical plug-in is displayed using the A horizontal time-base plug-in. This resembles the trace-slaving "ALT" mode that is produced by an 1A4 in a 547. Many other modes are available. It is possible to put vertical plug-ins in the horizontal slots for X-Y operation. It is even possible to put a horizontal plug-in in one of the vertical slots to produce a raster scan.
A special plug-in, the 7A21N, provides direct access to the deflection plates up to 1 GHz at an uncalibrated sensitivity of 4 V/Div. This plugin requires modifications to the mainframe to bypass the Y output amplifier (thus disabling readout and the other vertical plugin bay).
A rear-panel remote control connector has connections for single-sweep ready lamps, a reset button, and readout control.
Internals
The 7904 uses a switch-mode power supply and has no fan. The signal path is completely differential and the internal signal wiring is 50 Ω coax.
The Y delay line in the 7904 has a delay of 65 ns, which is too short for some older time bases such as 7B53 to display the trigger event. The CRT (154-0644-05) has distributed vertical deflection plates.
Thor Hallen designed the main vertical amplifier and the 7A19 plugin (Note 1). It used bridged T coils and the "ft doubler" circuit patented by Carl Battjes to achieve its bandwidth.
The 7904 makes extensive use of custom integrated circuits and hybrid circuits, inter alia, the 155-0064-00 470-ps output amplifier, 155-0022-00 analog multiplexer for channel switching, 155-0059-00 HF amplifier, 155-0095-01 and 155-0095-03 differential HF amplifiers, and 155-0067-02 SMPS controller.
Early 7904 have issues with horizontal aberrations for sweep rates of 1 ns/Div or faster. After discovery of the issue modification kits that replace the horizontal amplifier were offered. For more information see the table below and the manual of the 067-0657-00 Normalized Ramp Generator that was used to investigate and rectify this issue.
| Serial Number | A9 Horizontal Amp. | Issue | Modification Kit |
|---|---|---|---|
| B010000-B081987 | 670-1632-00 | Fully calibrated sweeps for rates of 1 ns/Div or faster requires a dedicated 7B92 (non A!) and the two units to be calibrated as a system. | 050-0636-01 |
| B081988-B219999 | 670-1632-01 | Can be calibrated to either work with magnifier timebases (7B70,7B80), or alternatively non-magnifying time bases (7B92A), but not both. | 040-0791-00 |
| B220000 and above | 670-1632-02/03 | None - fully compatible with all timebases and all sweep rates. | − |
Prices
| Year | 1972 | 1976 | 1980 | |
|---|---|---|---|---|
| Model | 7904 | 7904 | 7904 | |
| Mainframe only | Catalog price | $2,900 | $4,100 | $6,265 |
| In 2024 Dollars | $21,800 | $22,600 | $23,900 | |
| Mainframe with 7A19, 7A19 Opt. 04, 7B92 |
Catalog price | $5,500 | $7,765 | $12,015 |
| In 2024 Dollars | $41,300 | $42,900 | $45,800 |
Notes
- See 7A11 and John Addis, Good Engineering and Fast Vertical Amplifiers, in Jim Williams (Ed.), Analog Circuit Design: Art, Science and Personalities (1991), p.114, and Tektronix New Products 1972 brochure.
Pictures
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7904 (non-A) front
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7904 rear
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Left side. Left top: Vertical amplifier; left bottom: switch-mode power supply; right center: delay line; right bottom: plug-in bays
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Right side. Top left: calibrator; bottom left: plug-in bays; top center: readout board; top right: Z amplifier
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Right side detail. Left: calibrator; right: readout.
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Plug-in backplane board front (left trigger selector piggyback board removed)
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B Trigger selector piggyback board (A6)
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Vertical interface piggyback board (A7). The two 155-0095-03 amplifiers (large metal cans) are used to select the signal from one vertical plug-in bay, and drive the delay line.
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Plug-in backplane board rear
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Backplane board sandwich seen from below
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Horizontal (X) amplifier board (late >B220000)
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Vertical (Y) amplifier board
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Z amplifier board
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front-panel controls
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7904 block diagram
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Power Supply
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7904 switchmode power supply, covers removed
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View from right (as seen from front of instrument)
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Primary side circuit board
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Primary side capacitors
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Detail view of transformer from the side
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Switching transformer
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Secondary side rectifier board
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Secondary side post-regulator
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HV block, multiplier
Parts
Some Parts Used in the 7904