Tubes Asylum Questions about tubes and gear that glows. FAQ

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RE: im new to tube

Posted by truep (A) on June 18, 2007 at 14:11:37

In Reply to: im new to tube posted by sinq44 on June 18, 2007 at 08:57:55:

It depends on several factors. One is plate voltage. Lets say you are measuring across a 10 ohm resistor (very common). At a plate voltage of 400V at 75 Mv, the tube will dissipate 30 watts at idle (OK). If the plate voltage is 500V, the tube will dissipate 37.5 watts (high).

at 85 MV at 400V it would be 34 watts and at 450, 38.25 watts. Both too high for long tube life. Use the formula (with a 10 ohm cathode resistor)
V Across cathode resistor times plate voltage to calculate (.075 x 400= 30 watts.

Remember, the lower the plate dissipation, the longer the tubes last! In a properly designed circuit, I doubt you will hear any difference.

My VTL 160's are biased at 35 MV (17.5 watts) and sound great. At 25mv, I can hear a difference, bu I can't hear any difference at 45 MV.

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