221
From TekWiki
The Tektronix Type 221 is a miniature 5 MHz analog scope introduced in 1973.
It 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 1mA 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.
Specifications
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Pictures
Front
Panel of 221
Probe of 221
221 with orginal bag
221 on top of 565
