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Title: BAssman Bias Post by: mutron80 on January 14, 2009, 09:25:22 AM Hi,
I need de cathode current to adjust the bias. Thanks and sorry for my english. Title: Re: BAssman Bias Post by: wyatt 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 (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. |