[sdiy] Tube Synth web page update

René Schmitz uzs159 at uni-bonn.de
Fri Aug 23 22:40:42 CEST 2002

Hi Daniel!
>I have a small quantity of NOS Telefunken EM87 tubes that i want to 
>incorporate into my future modular as indicators. 
>Does someone have a schematic diagram of an indicator using that 

To indicate a voltage one does only need two extra resistors. One is the 
grid resistor, typically 1 Meg or so from grid to GND. And you will need 
a 100k resistor from pin 9 to 250V. Connect pin 9 to pin 7 (Anode of the
triode to the deflection electrode). The screen goes directly to 250V. 
Cathode to GND. With that you can steer the shadow in the tube via a 
voltage in the range 0V to -15V. So an opamp stage would be a good thing 
to display positive voltages as well.


uzs159 at uni-bonn.de


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