The Tektronix 581 is similar to the 585, but with simplified trigger and sweep circuitry. It was introduced in 1959. The vertical signal path of the 581 is the same as that of the 585. It uses the T581 CRT. There is also a 581A, which has tunnel diode triggering. 581A has bandwith 85Mhz instead of 100Mhz, because CRT-production has bad yield. Many CRT provide not reach 100 Mhz.