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The Tektronix 647A is a 100MHz scope that is designed to operate in a wide range of temperatures. 
The 647 is a 50 MHz oscilloscope with plug-ins for both vertical and horizontal deflection.  The intent was to offer a higher performance scope in a small form factor, roughly the size and weight of the 56x series.  The system is nearly all solid state, the exception of the three 5642 HV rectifier tubes used in the CRT circuit.  The 647 was promoted as “ruggedized” with an  extended operating temperature range, and higher shock and vibration ratings that previous lab grade instruments.  The 647 was introduced in late 1963, along with a minimal set of plug-ins.  It was replaced by the higher bandwidth 647A in 1967.
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
and 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 50MHz bandwidth. There is also an RM647A.  The 647 was [[introduced in 1963]] and has 14kv of acceleration
voltage on the CRT.  The 647A was [[introduced in 1967]].


The vertical amplifier contained in the 647A indicator unit (mainframe) is made of
The 647 uses 10 series vertical and 11 series time base plug-ins.  At introduction, the 10A2 a dual channel 50 MHz vertical, 11A1 single time base, and 11A2 dual time base were offered.  The plug-ins were unique to the 647 and 647A. Unlike the threaded knob used for retaining the 530/540 series plug-ins, the 647 used a lever actuated cam mechanism.  The single lever both engaged and disengaged the plug-in with a quick, smooth motion.  Many users considered it to be the best plug-in retaining system Tek had ever offered.
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
Unlike the 56x series where the plug-ins directly drive the CRT deflection plates, the 647 has amplifiers for both the vertical and horizontal signals in the mainframe.  In addition to supporting the higher bandwidth, the amplifiers provide a normalized gain at the plug-in interface, eliminating the need to adjust the gain or sweep cal every time a plug-in was swapped.  The vertical amplifier also contained a delay line.  The interface between the vertical plug-in and the mainframe 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.
at the outputs.


The horizontal amplifier in the 647A uses selected 2N3119 NPN bipolar transistors for the output. 
The horizontal and vertical plugs are not electrically interchangeable.  Only a 10 series plug-in will work in the vertical compartment, and only a 11 series time base will work in the horizontal compartment.  X-Y mode requires the use of the external horizontal input in an 11 series time base.
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.  Plug-ins that are compatible
with the 647 and 647A include the [[10A2]] and the [[11B2]].
 
 
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?
 
A Mod 165K version was available that was somehow ruggedized.


* [http://w140.com/kurt/647.pdf Tektronix 647 Manual (PDF)]
* [http://w140.com/kurt/647.pdf Tektronix 647 Manual (PDF)]
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