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Re: Ultrasonic AC for DHT Filament

Posted by dave slagle on March 6, 2003 at 18:05:40

In Reply to: Re: Ultrasonic AC for DHT Filament posted by Triode Kingdom on March 6, 2003 at 13:23:54:

interesting thoughts on the common mode path back to the ac source... but how does this explain AC sounding better? there is no common mode rejection from the line?

when you refer to different regulators sounding differently, are you referring to devices, or concepts??? that is LM317 vs LM338 or current vs voltage regs?

many prefer the current regs to voltage regs, and this fits into the ac current path logic, since the current source provides a high impedance (like a series choke) and the voltage reg provides a low impedance (big cap across the filament) each would behave differently to the signal currnet.

looking at batteries, we have the perfect isolation from the AC source, but we do not have the benefits of the single current path for AC since the battery behaves as a cap across the filament... and batteries like caps are nonlinear, and i just don't find it to be a good practice to put 1/2 of your signal current through a nonlinear device, either put all of it through it or none of it.

it would be easy enough to test this with a battery, just place a choke in series with the plus leg and see if there is a difference... better or worse isn't the issue, just different.

i do believe that even though they are nonlinear, batteries can offer a better result than a cap, i guess i have to since i much prefer batteries with all their nonlinearities in the cathode of my 6C45 input tube... but fwiw, all of my signal current must traverse the battery. (some people like bypassing caps with caps, others don't so it may just be a taste thing.)

the thought of two audio quality chokes in the filament legs makes me ask "why do we need to put one in the ground leg?" i mean it is ground.... this too would be easy enough to test... and the good news in this all is that most filament chokes are audio quality.... i won't get into suggesting a nickel core to improve the hf behavior...

like the first reply in the threas said... all of this theory is fine, but at some point a number of us have to try these things and objectively compare the results to see where the thoery holds.

dave

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