7904A
The Tektronix 7904A is a 500 MHz, non-storage 7000-series oscilloscope mainframe with four bays, introduced in 1984. It is a redesign of the predecessor model 7904 from 1971, using integrated circuits developed for the 1 GHz 7104.
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") |
| Trigger Source | Left / Vert Mode / Right |
| 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
- 7904A @ amplifier.cd
- Repairing front panel buttons of Tektronix 7904 oscilloscope
- Tektronix 7904A lab check in and LED MOD by Zenwizard Studios @ YouTube
Documents Referencing 7904A
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Internals
The 7904A incorporates a 65 ns Y delay line. This delay is too short for some older time bases such as 7B53 to display the trigger event. The signal path is completely differential and the internal signal wiring is 50 Ω coax. The CRT (154-0644-05) has distributed vertical deflection plates.
Differences to 7904
The 7904A borrows heavily from the 1 GHz 7104 introduced in 1978 in terms of front panel layout, mechanical design, and electronics, re-implementing the vertical amplifier using Hypcon-packaged amplifier chips such as the 155-0173-05, 155-0175-05 and 155-0178-05.
The 7904 had the elaborate 5-decade built-in calibrator with variable rate that was common on all first-generation 4-bay 7000-series scopes, it was dropped from the 7904A. The rear remote control connector unique to early 7000-series scopes was dropped as well. In the 7904A, The Control Illumination switch moved to the rear panel, and the readout system gained a pulsed mode in which it is synchronized with the sweep instead of interrupting the display at random times. This pulsed mode is not compatible with all time base plug-ins (see manual p. 1-12).
In addition, the 7904A adds a fan in the SMPS.
Prices
| Year | 1984 | 1990 | |
|---|---|---|---|
| Model | 7904A | 7904A | |
| Mainframe only | Catalog price | $8,810 | $12,750 |
| In 2024 Dollars | $26,600 | $30,600 | |
| Mainframe with 7A19, 7A19 Opt. 04, 7B92 |
Catalog price | $17,425 | $24,190 |
| In 2024 Dollars | $52,700 | $58,100 |
Pictures
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7904A
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7904A Rear
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7904A Top with Horizontal Amplifier at top right
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7904A Right with Z-axis on top right and 2nd Gen. Readout board at bottom right
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7904A Left with Vertical Amplifier (top) and Vertical switch board (bottom)
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7904A Topleft
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7904A Closeup of Vertical amplifier
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7904A Low-voltage Power Supply Schematic
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7904A Horizontal and vertical amplifiers
Parts
Some Parts Used in the 7904A