485
The Tektronix 485 is a dual-trace, portable analog oscilloscope with a maximum bandwidth of 350 MHz, introduced in March of 1972.
The impedance of the inputs can be set individually to 50 Ω or 1 MΩ. The scope achieves its maximum bandwidth when the inputs are in 50 Ω mode.
A distinguishing feature – at least in a portable oscilloscope of its period – is the Alternate Horizontal Mode. In this mode, the B timebase is shown in a separate full-width scan, as opposed to the more common Mixed Mode, where the B timebase is shown on the same line as the A timebase, after the delay time.
The 465, which was introduced after the 485, only received this feature in its "B" incarnation (465B).
Variant 485-1 omits the "A EXT Trigger display", as does variant 485-2 which additionally only has 50 Ω inputs.
John Addis was project leader for the vertical section, assisted by Wink Gross. Glenn Bateman, Ron Peltola and Bob Firth designed the low- and high-impedance attenuators. Murlan Kaufman was project leader for the horizontal and logic systems and designed the trigger generator. Bob White designed the trigger amplifier and external trigger view circuits. Keith Taylor did the work on the fast sweeps, the horizontal and the Z-axis amplifiers. Dick Troberg designed the high efficiency power supply system.
Key Specifications
| Input Impedance | 50 Ω / 1 MΩ // 20 pF |
|---|---|
| Rise time | 1 ns (50 Ω) / 1.4 ns (1 MΩ) |
| Bandwidth | 350 MHz (50 Ω) / 250 MHz (1 MΩ) |
| Deflection | 5 mV/div to 5 V/div in 1−2−5 sequence, 2% accuracy |
| Time Base | 1 ns/div to 0.5 s/div in 1−2−5 sequence |
| CRT | 154-0652-00 and 154-0652-05, 21 kV acceleration, 8 × 10 divisions (0.8 cm/div) |
| Weight | 9.3 kg (21.5 lb) |
| Power | AC 90–136 or 180–272 V, 48–440 Hz, 60 W @ 115V |
Links
- Gene Andrews, A nanosecond portable oscilloscope. In Tekscope Vol.4 No.2, March 1972, p.2+.
- Tek 485 @ amplifier.cd
- 485 troubleshooting @ YouTube
- 485 Restoration and Repair @ Zenwizard Studios YouTube
- 485 Power Supply and Tube Alignment @ Zenwizard Studios YouTube
- 485 Horizontal Alignment @ Zenwizard Studios YouTube
- 485 Vertical and Trigger alignment @ Zenwizard Studios YouTube
Prices
| Year | 1972 | 1973 | 1976 | 1986 |
|---|---|---|---|---|
| Catalog Price | $4,200 | $4,200 | $4,550 | |
| In 2023 Dollars | $30,900 | $29,100 | $24,600 |
Internals
The 485 includes a switching power supply and uses custom integrated circuits for most of the gain blocks. Triggering uses tunnel diodes.
Pictures
External
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Time base A, External trigger display switch
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Internals
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Top, Horizontal Amp board
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Underside, Power supply, A-Trig board
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LHS, Vertical Amp board
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RHS, Sweep/Inverter board
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A-Trigger board
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Vertical attenuator Assy
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Vertical attenuator Assy, 50Ω Board
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Vertical attenuator Assy, Hi-Z Board
