7904A

Manuals – Specifications – Links – Pictures

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 7A29 or 7A19 amplifier)
Fastest calibrated sweep	500 ps/div with 7B10, 7B15, or 7B92A
Outputs	Vertical Signal Out (25 mV/Div into 50 Ω, 0.5 V/Div into 1 MΩ); +Sawtooth; +Gate; camera power; probe power
Z axis input	+2 V to blank from max. intensity, –2 V to unblank from min, intensity; 1 MHz BW; 470 Ω // 50 pF; max. 15 V DC+ peak AC
CRT	Acceleration voltage 24 kV (+21 / –3 kV) Standard: 8×10 Div @ 1 cm, P31 (green): 154-0644-05/154-0893-05, 1.25 cm/ns Option 78, 8×10 Div @ 1 cm, P11 (blue): 154-0644-09, 2.5 cm/ns Option 4, 8×10 Div @ 0.5 cm, P31 (green): 154-0661-05, 2 cm/ns Option 13, 8×10 Div @ 0.5 cm, P11 (blue): 154-0661-10, 4 cm/ns
Calibrator	1 kHz square wave, 40 mV to 4 V in decade steps (4/40/400 mV into 50 Ω); 40 mA current loop
Power	90−132 V or 180−250 V, 48−440 Hz, 210 W nom.
Weight	16.9 kg (37.2 lbs) without plugins
Dimensions	34.5 cm × 30.5 cm × 57.7 cm (13.6 in x 12.0 in x 22.7 in) H×W×L
Options	Opt.1: deletes read out system Opt.2: X-Y delay compensation network Opt.3: Extra EMI shielding Opt.4: Maximum-brightness CRT with reduced area Opt.78: P11 phosphor

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

Custom ICs used in the 7000 series readout system

Page	Model	Part nos	Description	Designers	Used in
155-0014-01	M019D	155-0014-00 • 155-0014-01	analog-to-decimal converter	Barrie Gilbert	7000 series readout system • 7854 • 7934 • 7J20 • 7L5 • P7001
155-0015-01	M020F	155-0015-00 • 155-0015-01	analog data switch	Barrie Gilbert	7000 series readout system • 7854 • 7934
155-0017-00	M025	155-0017-00	5 MHz decade counter	Barrie Gilbert	7000 series readout system • 7854 • 7934
155-0018-00	M026	155-0018-00	zeros logic control	Les Larson	7000 series readout system • 7934
155-0019-00	M027	155-0019-00	decimal point and spacing control	Les Larson	7000 series readout system
155-0020-00	M028	155-0020-00	output assembler	Les Larson	7000 series readout system
155-0021-00	M029C	155-0021-00 • 155-0021-01	timing generator	Les Larson	7000 series readout system • 7854 • 7934
155-0023-00	M160	155-0023-00	character generator (0 1 2 3 4 5 6 7 8 9)	Barrie Gilbert	7000 series readout system
155-0024-00	M161	155-0024-00	character generator (↓ < I / + - + C Δ >)	Barrie Gilbert	7000 series readout system
155-0025-00	M162	155-0025-00	character generator (m μ n p X K M G T R)	Barrie Gilbert	7000 series readout system
155-0026-00	M163	155-0026-00	character generator (S V A W H d B c Ω E)	Barrie Gilbert	7000 series readout system
155-0027-00	M164	155-0027-00	character generator (U N L Z Y P F J Q D)	Barrie Gilbert	7000 series readout system