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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 8114 times)
mutron80
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« on: January 14, 2009, 09:25:22 AM »

Hi,
I need de cathode current to adjust the bias.

Thanks and sorry for  my english.
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wyatt
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« 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. 
http://www.webervst.com/tubes1/calcbias.htm

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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