Re: Cathode Bias PP tail questions?

Posted by Gary P (A) on April 27, 2005 at 19:57:55

In Reply to: Cathode Bias PP tail questions? posted by danlaudionut on April 27, 2005 at 10:55:29:

My experience so far working with the PP pentode circuits like the Tabor and 47PP has shown the following.

When using a resistor the amps sounded better with the resistor bypassed.

The CCS on the cathodes sounded better to me and everyone else that have heard both versions.

The 2 variations work in fundimentally different ways.

The bypassed resistor works as described in a post just below, with the bypass capacitor closing the circuit path for the imbalance currents caused by tube mismatch.

The CCS version allows the grid to cathode voltage of each tube to be fine tuned on the fly to make the tubes act as if they were perfectly matched.

The un-bypassed resistor doesn't provide a path for the imbalance currents and doesn't allow the tubes to adjust the grid to cathode voltages to match up either. Worst of both versions.

The above observations were in DC coupled circuits where the cathode resistor was dropping lots of voltage and was a higher value than normally found in RC coupled amplifiers. With lower value cathode resistors the unbypassed resistor version will proabably act more like the bypassed resistor.

Gary

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Follow Ups Full Thread

Topic - Cathode Bias PP tail questions? - danlaudionut 10:55:29 04/27/05 (14)

Re: Cathode Bias PP tail questions? - Gary P 04/27/0519:57:55 04/27/05 (4)

Re: Cathode Bias PP tail questions? - MIchael Samra 17:43:52 04/28/05 (0)

Have you tried the WE connection on a CCS? - Mark Kelly 20:23:37 04/27/05 (2)

Re: Have you tried the WE connection on a CCS? - danlaudionut 20:41:29 04/27/05 (1)

Re: Have you tried the WE connection on a CCS? - Gary P 21:50:06 04/27/05 (0)

Haven't tried CCS. - Mark Kelly 16:38:36 04/27/05 (0)

For an 845, why not use fixed bias? - Russ57 11:49:30 04/27/05 (7)

Re: For an 845, why not use fixed bias? - MIchael Samra 17:19:03 04/28/05 (0)

Let me try again ... - danlaudionut 14:32:49 04/27/05 (1)

Just read Gary P's article .. - danlaudionut 15:17:46 04/27/05 (0)

Because Fixed Bias.................. - drlowmu 13:45:13 04/27/05 (2)

Re: Because Fixed Bias.................. - Russ57 15:32:32 04/27/05 (1)

Re: Because Fixed Bias.................. - drlowmu 10:42:59 05/2/05 (0)

Re: For an 845, why not use fixed bias? - kadyquil2 13:14:31 04/27/05 (0)

Follow Ups

Re: Cathode Bias PP tail questions? - Gary P 04/27/0519:57:55 04/27/05 (4)

Re: Cathode Bias PP tail questions? - MIchael Samra 17:43:52 04/28/05 (0)

Have you tried the WE connection on a CCS? - Mark Kelly 20:23:37 04/27/05 (2)

Re: Have you tried the WE connection on a CCS? - danlaudionut 20:41:29 04/27/05 (1)

Re: Have you tried the WE connection on a CCS? - Gary P 21:50:06 04/27/05 (0)

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