647
The Tektronix 647A is a 100MHz scope that is designed to operate in a wide range of temperatures. It takes two plug-ins, one for vertical, one for horizontal/sweep. It uses 10-series and 11-series plug-ins. The plug-ins resemble those that go in a 560-series scope, like the 3A3 and 3B2 plug-ins, but they are quite different are not at all compatible. The 647A contains vertical and horizontal amplifiers, whereas in the 560-series, the plug-ins drive the deflection plates directly. The 647A followed the Type 647, which is similar but has 60MHz bandwidth. There is also an RM647A.
The vertical amplifier contained in the 647A indicator unit (mainframe) is made of NPN and PNP bipolar transistors. The output transistors, Q484 and Q494, are selected 2N3866 NPN transistors. The datasheet for the 2N3866 lists Ft as 800MHz and specifies an absolute maximum value of Vceo of 30V. The quiescent value of Vce on Q484 and Q494 is about 30V. So it seems likely that the selection process for these transistors involved testing their performance at the high end of their specified voltage range, and probably beyond.
The power supply of the 647A is all solid state, with a zener voltage reference and NPN pass transistors at the outputs.
The horizontal amplifier in the 647A uses selected 2N3119 NPN bipolar transistors for the output. These are specified as having and Ft of 250MHz and a Vceo max of 80V.
The interface between the vertical plug-in and the indicator unit is a 93-ohm controlled-impedance connection. This is in contrast to the 500-series scopes, which appear to the plug-in as a high impedance. For example, there is a cathode follower immediately after the plug-in connector in a 547. Notable exceptions are the 585 and 585A, which interface the signal from plug-in to the scope at a 93-ohm impedance, like the the 647A.
Is it the only scope to use those plug-ins? It is unusual to see only one scope in what appears to be the beginning of a series. Was it discontinued because of lack of demand? What replaced it?
The 647 is similar to the 647A, but the bandwidth is 50MHz.