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. 600V (DC + Peak AC) or 600 Vp-p AC
Sweep Range	200 ms to 1 μs, 17 steps
CRT	154-0705-00, 6(V) × 10(H)
Operating Time on Battery	2-3 Hours
Internal Battery	10 Rechargeable NiCd cells
Line Voltage	90-250V AC 48 Hz - 62 Hz, 80-250V DC
Power Consumption	5W @250 V
Dimensions	(H/W/D) 3" × 5.25" × 9" (7.6 cm x 13.2 cm x 22.8 cm)
Weight	3.5 lbs/1.5kg

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 and the other drives the bottom plate.

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

MOD 290A is found on a version 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