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Amplified Parts
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|-+  American Style
| |-+  5F6-A Bassman
| | |-+  BAssman Bias
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Author Topic: BAssman Bias  (Read 8108 times)
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« on: January 14, 2009, 09:25:22 AM »

I need de cathode current to adjust the bias.

Thanks and sorry for  my english.
« Reply #1 on: January 14, 2009, 11:39:23 AM »

If you haven't already done so, you measure the Plate Voltage coming off pin 8 of the rectifier.  Careful doing so, it's high voltage. 

Then you measure the voltage from Pin 8 of each power tube socket to Ground (red probe on pin 8 of the socket, black probe on a chassis ground), this will be in milliVolts.   1mV=1mA of cathode current thanks to the 1-ohm resistor running from pin 8 of the power tube sockets to ground.

At the top of this page, select your power tube style and enter your plate voltage. 

It will tell you what the cathode current should be for ~70% dissipation.  Adjust the bias pot and keep checking cathode current until you get the tubes in the ballpark.
« Last Edit: January 14, 2009, 11:41:00 AM by wyatt » Logged
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