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. One of the world's first commercially marketed storage scopes. Brian Kline tells me: "I would argue that the Hughes 104 Memo scope probably preceded the Tektronix 564 as a commercial product. It was a mostly if not entirely vacuum tube design using printed circuit boards. The biggest problem with the 104D was it's limited bandwidth of about 300 KHz." Unfortunately, neither of us knows when the 104D was made, so we are unable to ascertain which one gets the "first" label. What I do know is that the bistable storage technique came from Hughes originally, so the Hughes Memo scope might indeed have been first. Made until 1968, the type 564 is a bit smaller than the others. It accepts Tek 2- and 3- series plugins, and has a bandpass of approximately 10 MHz, when equipped with the right plugins. This scope does not have a fan, but it seems to cope quite well without, judging by the fact that it is still working.