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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Re: No such thing posted by danlaudionut on April 24, 2007 at 06:10:13:
Russ is right; there is no rating for plate current. The plate is primarily damaged by heat which is the product of voltage and current. There is a rating for plate dissipation, 25 watts for the EL34.The screen grid also has a dissipation rating of 8 watts. In triode mode the two can be combined for a total dissipation of 33 watts.The current limit is at the cathode. The EL34 is rated for 150 mA of cathode current. This is average current, not peak current. Class A amps will sometimes be bias at or near this current but the plate voltage must be low enough to prevent over dissipating the plate. In class AB amps the idle current is generally much less than this limit and the plate voltage is higher than the class A amp so the plate dissipation still limits the idle current. In class AB amps the cathode current rises as the output power rises and at full power it can easily approach the rating limits.
Keep in mind that the cathode current is the sum of plate current, screen grid current and control grid current. Since most audio amps do not drive the control grids positive there is no grid current (class AB2 amps are an exception). When designing an amp all these parameters need to be included in the design process so as not to risk exceeding the tubes ratings.
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Follow Ups
- Re: No such thing - beermanpete@socal.rr.com 23:43:49 04/27/07 (0)
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