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Re: Variable power resistors - cathode bias?

3/4/1998 1:22 PM

J Fletcher

Re: Variable power resistors - cathode bias? I rebuilt my Princeton Rev for the umpteenth time a couple of weeks ago,cathode biased 6L6's,plate voltage=360,with a 270ohm cathode resistor,and an old Ampeg transformer with a primary impedance=6600ohms.Man,does it sound great.Sounds way louder than I expected,to boot.Puts out about 20 watts.In fact,I decided to build a 4 6L6 version with 2 12's and see what it would be like on stage.Idles pretty hot compared to a fixed bias amp,so I was considering a fan.I am considering the idea of using the cathode current to drive a fan of suitable voltage to help cool things down.Hate to waste that power that the resistor consumes.I've seen schematics of amps which use this current to heat the filaments of 12ax7's.Ever try that?Seems that the voltage isn't regulated well enough for that purpose,but might be ok for a fan.I've noticed that cathode biased amps have lots of idle current,usually greater than 50ma per tube,where do you set yours?Do you"ear ball"it in?How about screen voltages?Transformer impedance?I've looked in the RCA Tube manual for their recommendations,but was interested in real world(ie. rock and roll)experiences.....

 

Replies:

Whit Hi Jerry, Been a while sin... -- 3/4/1998 2:24 PM John Kos I would quickly guess that running ... -- 3/4/1998 3:21 PM stephen You might get satisfactory results ... -- 3/8/1998 12:46 PM