RE: ... "bunk" ... so you think ???

Posted by dave slagle (M) on May 28, 2012 at 18:56:04

In Reply to: ... "bunk" ... so you think ??? posted by drlowmu on May 28, 2012 at 15:04:55:

Your argument doesn't make any sense since ground and symmetry have everything to do with hum cancellation but little to do with how the tube biases up.

When you consider AC heating you need to bring the aspect of time into the mix to consider the possible voltage gradients. assuming you start a sine at 0, in 4ms you have a voltage gradient of +3.5V. At 8ms the filament is at the same potential from end to end. 12ms puts you at -3.5V and 16ms (ok (1/60ms) puts you back to the beginning to repeat. This means a 2A3 gives a 7V change in bias over time which is worse than a DC heated 6A3.

Furthermore, the bias in a DC heated tube is fixed. In an AC heated tube it is a moving target. Take a 1Khz signal and look at how the bias shifts in time. With a DC heated tube every trace of the sine will see the same stable bias. With AC, the single 1Khz waves at about 4ms and 12ms will see an overall shift in bias of 7V which some actually call IM distortion.

By no means am I saying that DC is better and in fact I like AC whenever I can get away with it. I am just stating my view that the concept of the "voltage gradient" or "bias shift" on a DC heated tube is a silly one to me since with AC it is actually worse.

dave

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Follow Ups Full Thread

Topic - PSE 2a3 operating points? - andy evans 02:33:23 05/26/12 (24)

RE: PSE 2a3 operating points? 320V @45mA 5K Fine - Minussss3db 11:18:29 05/26/12 (5)

RE: PSE 2a3 operating points? 320V @45mA 5K Fine - andy evans 13:09:13 05/26/12 (4)

Separate Cathode Rs for PSE - Naz 22:11:18 05/28/12 (2)

RE: Separate Cathode Rs for PSE - andy evans 00:36:14 05/29/12 (1)

Fixed Bias can be done in so many ways - Naz 01:09:39 05/29/12 (0)

RE: PSE 2a3 operating points? 320V @45mA 5K Fine - drlowmu 17:14:46 05/26/12 (0)

RE: PSE 2a3 operating points? - Neff 09:15:51 05/26/12 (0)

RE: PSE 2a3 operating points? - euro21 03:43:08 05/26/12 (16)

RE: PSE 2a3 operating points? - andy evans 04:50:47 05/26/12 (15)

Do you need PSE ???? - drlowmu 05:45:58 05/26/12 (14)

RE: Do you need PSE ???? - dave slagle 15:53:32 05/26/12 (10)

... "bunk" ... so you think ??? - drlowmu 15:04:55 05/28/12 (3)

DC Vs AC filaments aside ... - Naz 00:20:10 05/29/12 (0)

RE: ... "bunk" ... so you think ??? - dave slagle 18:56:04 05/28/12 (1)

RE: ... "bunk" ... so you think ??? - drlowmu 07:44:59 05/29/12 (0)

RE: Do you need PSE ???? - Tre' 11:01:35 05/28/12 (2)

RE: Do you need PSE ???? - dave slagle 19:20:30 05/28/12 (1)

phase cancellation? - shane. 02:24:01 05/30/12 (0)

RE: Do you need PSE ???? - drlowmu 16:40:55 05/26/12 (2)

Not Quite Right... - Triode_Kingdom 05:54:06 05/30/12 (0)

you CAN"t be serious ... - mikeyb 10:00:25 05/29/12 (0)

RE: Do you need PSE ???? - andy evans 07:02:43 05/26/12 (2)

RE: Do you need PSE ???? - drlowmu 08:12:17 05/26/12 (1)

RE: Do you need PSE ???? - andy evans 09:55:59 05/26/12 (0)

Follow Ups

RE: ... "bunk" ... so you think ??? - dave slagle 18:56:04 05/28/12 (1)

RE: ... "bunk" ... so you think ??? - drlowmu 07:44:59 05/29/12 (0)

RE: ... "bunk" ... so you think ???

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