gofar99 Messages: 1986 Registered: May 2010 Location: Southern Arizona
Illuminati (5th Degree)
Hi, I agree that you are indirectly measuring the cathode current. In my class A push-pull designs I run the EL34s and KT77s at 62ma per tube, KT88s at 90ma each and KT120s at 155ma each - all at 450-475 volts B+. Cathode voltages (which effectively subtract from the applied B+ run from low 20's to high 40's). For AB use it would be about 2/3 that much and B use about 1/2. I try to keep tube dissipation under about 85%. Then tube life is nearly forever. Many power tubes are rated at the 100% level and then the hours of use until they are considered no good varies from 2000 to 5000 hours. I would set your amp at the manufacturer's recommended values for best performance.
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