485
The Tektronix 485 is a dual-trace, portable analog oscilloscope with a maximum bandwidth of 350 MHz. 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.
The 485 was introduced in March of 1972. It includes a switching power supply and uses custom integrated circuits for most of the gain blocks. Triggering uses tunnel diodes.
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. At the same time, the section shown with the B timebase is shown highlighted in the A scan.
The 465, which was introduced after the 485, only received this feature in its "B" incarnation (465B).
The 485 uses the 154-0652-00 and 154-0652-05 CRTs.
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 |
Links
- Tek 485 @ amplifier.cd
- 485 troubleshooting @ YouTube
Maintenance issues
A healthy Tek 485 CRT has been observed to have a filament current of 98 mA. A broken Tek 485 CRT that lost its vacuum was observed to have a filament current of 153 mA.
