565: Difference between revisions

574 bytes added ,  17 May 2015
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and then is discriminated by a [[6DJ8]]-based Schmitt trigger.
and then is discriminated by a [[6DJ8]]-based Schmitt trigger.
    
    
The 565 is also unusual in that it employs a [[tunnel diodes|tunnel diode]] in the trace intensification circuit.  The tunnel diode forms as a bistable multivibrator: kick it one way and it turns on and stays on, kick it the other way and
The 565 is also unusual in that it employs a [[tunnel diodes|tunnel diode]] (D845, a [[TD4]], which is equivalent to the [[1N3718]]) in the trace intensification circuit.   
it turns off and stays off.
The tunnel diode forms a bistable multivibrator: kick it one way and it turns on and stays on,  
kick it the other way and it turns off and stays off.  The tunnel diode is DC-coupled to the base-emitter junction of Q843,
which is a 2N404 germanium PNP transistor.  Because the tunnel diode and transistor are DC-coupled, the transistor needs
to be germanium.  This is one of the rare cases when a failed germanium transistor cannot be replaced with a silicon part.
Contrast this with the timebase A trigger of the [[585|585A]], which uses a tunnel diode AC-coupled to a transistor, which
makes the forward voltage of the transistor's base-emitter junction irrelevant.


=== Calibrator ===
=== Calibrator ===