221

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The Tektronix Type 221 is a miniature 5 MHz analog scope introduced in 1973.

Key Specifications

Bandwidth	DC to 5 MHz
Input Impedance	1 MΩ // 29 pF
Input Voltage	max. 600 V DC + Peak AC, or 600 Vp-p AC
Sweep Range	200 ms to 1 μs, 17 steps
CRT	154-0705-00, 6 Div (V) × 10 Div (H), 1 kV acceleration
Operating Time on Battery	2-3 hours
Internal Battery	10 rechargeable NiCd cells
Line Voltage	90-250 VAC @ 48−62 Hz, or 80-250 VDC
Power Consumption	5 W @ 250 V
Dimensions	(H/W/D) 3" × 5.25" × 9" (7.6 cm × 13.2 cm × 22.8 cm)
Weight	3.5 lb (1.5 kg)

Internals

The 221 has a switching power supply and built-in rechargeable batteries (which are a maintenance issue). It has a transformer-coupled trigger circuit which would seem to preclude DC level-based triggering. The trigger circuit uses a 1N3713 1 mA tunnel diode. The vertical output amplifier that drives the CRT plates is two opamps made from discrete transistors. One drives the top deflection plate, the other the bottom plate.

The power supply in the 221 uses the 120-0876-00 transformer.

The 221 contains one integrated circuit, a 741 opamp that creates a virtual ground, otherwise only discrete (including dual) transistors.

MOD 290A is a version of the 221 made for IBM, which adds a Single Sweep function, and a "Property of IBM" engraving.

Pictures

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  Front

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  Panel of 221

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  Probe of 221

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  221 with orginal bag

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  221 on top of 565

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  MOD 290A variant for IBM

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  MOD 290A variant for IBM