Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: 12BZ7 posted by tz7 on June 10, 2012 at 17:00:55:
Regarding the use of AC vs DC for indirectly heated tubes, bear in mind that DC heating provides constant temperature based on constant voltage. With AC heating the *average* amount of heating is the same, for sure, but the *peak* heating power is twice the average. You can think of there being small 120Hz "waves" of heat, on top of a constant flow of heat, flowing from the heater wire through the insulator to the cathode sleeve and thence to the coating. These will be small, to be sure, based on the thermal inertia of the heater wire, insulation and cathode sleeve, but the peaks of these waves will result in some small increase in the space charge around the cathode. This may explain why some folks notice an increase in "drive" from AC heating, since the increased space charge would result in a higher Gm and make the tube sound "newer" (in the sense of age, not date of manufacture).
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- RE: 12BZ7 - alfina 13:09:25 06/18/12 (0)