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Android Tube Bias Calculator

By Rob Robinette

The Tube Bias Calculator is free and available here in the Google Play Store.

I have been told that some anti-virus software is flagging the Tube Bias Calculator as "potentially harmful." The Tube Bias Calculator was created using MIT's Appinventor 2 programming environment and some anti-virus programs will flag anything created with it. You can Google "appinventor 2 virus" and see it is a common problem. If this happens to you I assure you that my Tube Bias Calculator does nothing but calculate tube bias.

WARNING: Amplifiers have high voltage that can KILL. Do not attempt to set an amplifier's bias unless you are competent with test gear and very familiar with the dangers involved.

Enter the values in the yellow boxes and touch the 'Calculate'button.

 

 

Find Tube's Max Safe Bias

Find your tube in the selection list. After selecting the tube the tube's maximum dissipation rating is shown to the right of the tube box.

Enter the measured Plate-to-Cathode Voltage (voltage between the plate and cathode tube socket pins).

Touch 'Calculate' and your tube's maximum safe bias currents are calculated. Single power tube amps are normally Class A. Multiple power tube amps are usually Class AB.

Touch the 'Help' button to open the help page.

Max Safe Class A Bias = 90% x Max Dissipation / Plate Voltage

Max Safe Class AB Fixed Bias = 70% x Max Dissipation / Plate Voltage

Max Safe Class AB Cathode Bias = 100% x Max Dissipation / Plate Voltage

 

Tube Dissipation Using Plate Current

Enter the Plate-to-Cathode Voltage which is the DC voltage measured between the plate and cathode tube socket pins. For octal tubes pin 3 is the plate and pin 8 is the cathode. For 9-Pin tubes like the EL84 the plate is pin 7 and the cathode is pin 3.

Enter the measured Plate Current in milliamps.

Touch 'Calculate' and the Plate Current, Dissipation and Dissipation% are shown.

 

Tube Dissipation Using Voltage Drop

Enter the Number of Tubes that share the cathode resistor.

Enter the Voltage Across the Cathode Resistor (voltage drop). To measure voltage drop across a resistor set your multimeter to DC volts and put one meter probe on each resistor leg.

Enter the Cathode Resistor resistance in ohms.

Enter the measured Plate-to-Cathode Voltage which is the DC voltage measured between the plate and cathode tube socket pins. For octal tubes pin 3 is the plate and pin 8 is the cathode. For 9-Pin tubes like the EL84 the plate is pin 7 and the cathode is pin 3..

Touch 'Calculate' and the Total Cathode Current is calculated. Total Plate Current is Cathode Current minus a 5.5% screen current. Divide the Total Plate and Current values by the Number of Tubes and you get Plate Current, Dissipation and Dissipation % per Tube.

If you prefer working with spreadsheets here's my Tube Bias Spreadsheet for Excel and OpenOffice.

Have comments or corrections? Email rob at: robinette at comcast dot net


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