Re: rectified cathodes and "ground"

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In Reply to: Re: rectified cathodes and "ground" posted by hifitom on November 1, 2001 at 15:31:29:

Yo Tom,
The rectifier will pass the signal AC because its all positive varying voltage, not positive/negative like the stuff coming out of the wall. Tubes are positive voltage only devices, thus you are generating a varying "AC" signal by going from +10V to +20V and back to +10V (or whatever).
The cap is only in the cathode return circuit to reduce neg feedback, not to provide a path for the signal to ground - the signal will pass thru the cathode resistor (or rectifier/diode/etc) just fine. But it changes the DC bias point if its not shorted by a cap. That +10/+20/+10 cycle I mentioned above will affect the operating point if its not shunted thru the cap. I think this is why some folks are trying regulator tubes - they maintain a constant voltage within a reasonable range which is exactly what the cathode bypass cap does.
Your question about the effects of connecting the cathode return directly to the PS ground is good - and is addressed by designs like Jack Elliano's Ultrapath, and some variations of parafeed where they connect the parafeed cap directly to the cathode of the tube which eliminates the PS from the signal return loop completely. I know my Ultrapath preamp sounds very clean with the signal shunted straight to the cathode. Unfortunately, it doesn't help with DC powersupply noise.
Sorry, I don't know the voltage drops of the tubes you mentioned.
Hope this helps. I've been following your experiments with rectifier tubes so keep the posts comin'. You wouldn't believe the combinations of caps I've tried to minimize the cathode bypass cap "sound".
Cheers,
Pete

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Follow Ups Full Thread

Topic - rectified cathodes and "ground" - hifitom 22:56:18 10/31/01 (6)

Re: rectified cathodes and "ground" - J Epstein 12:26:57 11/02/01 (0)

BTW...great answer to the guy (below)... - petef 11:42:55 11/01/01 (0)

Re: rectified cathodes and "ground" - petef 11:25:26 11/01/01 (3)

Re: rectified cathodes and "ground" - hifitom 15:31:29 11/01/01 (2)

Re: rectified cathodes and "ground" - petef 08:09:33 11/02/01 (1)

Thanks Pete & Jeremy! - hifitom 19:38:01 11/02/01 (0)

Follow Ups

Re: rectified cathodes and "ground" - petef 08:09:33 11/02/01 (1)

Thanks Pete & Jeremy! - hifitom 19:38:01 11/02/01 (0)

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