500 Series plug-in interface: Difference between revisions
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==Signal | ==Signal Input Impedance and Spoiler Switch Hole== | ||
The input impedance of 500-series scopes presented to the plug-in at pins 1+3 is approximately kept constant by adding shunt capacitors at the input depending on the tube type used. Early, scopes like the [[536]] and the [[555]] use a [[12BY7]] differential amplifier in the input stage, and the plug-in is loaded with the grid input capacitance with 2x 27 Ω (555) or 47 Ω (536) in series. Later, medium speed scopes like the [[545B]] and the [[549]] use dual input followers with a [[6DJ8]] tubes and 2x 47 Ω in series at the grids, so to keep the plug-in loading approximately constant a 3.9 pF capacitor is placed across pins 1 and 3 in the scope. | The input impedance of 500-series scopes presented to the plug-in at pins 1+3 is approximately kept constant by adding shunt capacitors at the input depending on the tube type used. Early, scopes like the [[536]] and the [[555]] use a [[12BY7]] differential amplifier in the input stage, and the plug-in is loaded with the grid input capacitance with 2x 27 Ω (555) or 47 Ω (536) in series. Later, medium speed scopes like the [[545B]] and the [[549]] use dual input followers with a [[6DJ8]] tubes and 2x 47 Ω in series at the grids, so to keep the plug-in loading approximately constant a 3.9 pF capacitor is placed across pins 1 and 3 in the scope. | ||