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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: Current draw at idle is nice, but it is only a piece of the pie posted by Tweaker456 on February 19, 2014 at 11:55:58:
Emission tests measure the ability of the cathode to emit electrons. Transconductance measures the gain of the tube, more specifically dVg/dVp, or the ratio of the effectiveness of grid voltage at controlling the plate current to the effectiveness of the plate voltage at controlling the plate current under conditions of some reasonable bias conditions and constant plate current.
Emission is useful for testing the life remaining in the tube, and transconductance is useful for gain matching. In an amp that has an "ac balance" control in the power amp transconductance matching is unimportant. If dc balance is available emission matching is unimportant except to test "health" of the tube.
When you buy matched tubes, be careful to ask how they were matched and be aware of what kind of matching is important for your amp. There are lots of claims of matched tubes, and sometimes that can mean as little as same manufacture and date code!
Most tube testers measure emission OR transconductance, but not both. A tube curve tracer will give you both sets of information.
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Follow Ups
- Emission and Transconductance - Lee of Omaha 12:03:12 02/20/14 (1)
- RE: Emission and Transconductance - Tweaker456 12:34:19 02/20/14 (0)
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