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C4S performance vs voltage drop

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Is there a sweet spot or a voltage differential that gives the best sonics with the C4S feeding .
I am going to feed my VR tube stack from one. The vr tubes work better with a large shunt feeding resistor and the associated higher B+.I just wondered if it was the same or opposite
since we are using SS devices.

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Re: C4S performance vs voltage drop - Paul Joppa 14:52:58 04/06/06 (7)
The C4S works well with a voltage drop (compliance) between 5 volts and 300 volts. I like to use at least 20% of the regulated voltage, to allow for some variation in the supplied voltage from the power line.
- Re: C4S performance vs voltage drop - DHT 4 ME 15:42:49 04/06/06 (6)
  Thanks Paul
  Just to push it a bit farther, I might use one in my 845 amp. It drops 1020v to 385v for the 10Y. I guess I was wondering if the sonics were better with a higher differential as I do have room to burn. I also have a 160v drop in the 26 pre. Obviously I could set it just about anywhere in between but am always looking for some profound advice.
  Thanks
  Bob Park
  - Re: C4S performance vs voltage drop - Doc B. 07:26:42 04/07/06 (5)
    The highest B+ you can handle with a C4S in the traditional setup where the LED bias resistor is grounded is 375V - with an MJE5731 in place of the MJE350. For kV type B+ you should probably use a tube type active load. Or you could try IXYS fuses, I mean, chips, and drop the input voltage on the chip down to it's 450V max rating with a resistor or regulator.
    As long as there is enough compliance to allow the tube to go to it's full output swing without running out of voltage headroom you are OK. We haven't found that large amounts of headroom above that compliance level make much difference.
    FWIW we are going to be doing a little more experimentation on active loaded output stages soon - on a lot smaller scale than a 1kV 845 amp...
    - What does this mean? - drsx 22:01:12 04/07/06 (3)
      Or you could try IXYS fuses, I mean, chips
      I know what the IXYS chips are. Does this mean something?
      - Re: What does this mean? - Doc B. 13:02:08 04/08/06 (2)
        
        In Reply to: What does this mean? posted by drsx on April 7, 2006 at 22:01:12:
        
        They blow up pretty easy. Paul Stubblebine literally buys them by the dozen to keep his IXYS chip loaded amps running.
        
        Re: What does this mean? - drsx 01:48:42 04/09/06 (1)
        
        In Reply to: Re: What does this mean? posted by Doc B. on April 8, 2006 at 13:02:08:
        
        Interesting and good to know. Tubelab.com claims that they are one of his preferred ccs's soundwise, and has not mentioned them blowing. He has mentioned that they oscillate pretty easily and that this can be quelled by adding a 1K stopper to the G terminal.
        http://tubelab.com/Simple45.htm (Open in New Window)
        
        Re: What does this mean? - Doc B. 10:34:23 04/09/06 (0)
        
        In Reply to: Re: What does this mean? posted by drsx on April 9, 2006 at 01:48:42:
        
        It might be that that his dismissal of the C4S on the grounds of the 2N2907 wanting 4-5 volts of bias is based more on theory than practice. I feel that the much higher impedance of the C4S (like 5Megohm+ vs. about 500Kohm) yields and audible improvement over the IXYS chip.
        We resorted to the IXYS chip for scenarios where the C4S couldn't handle the supply voltage, that is, it was a second choice. My bias is based on some bad experiences with more demanding applications. I once sat down with JT and watched him blow something like 10 of the 900V IXYS chips in a row, trying various combinations of stoppers and capacitor bypass to keep it from oscillating when used as a load on a 300B output stage. An afternoon JT spent with the design engineers at IXYS, trying to sort out the problem, yielded not much more than shrugging shoulders. Paul Stubblebine has probably replaced 10 or more 450V IXYS chips in his fleet of six PP300B amps, where they are used in parallel as a current sink on the cathodes of the 300Bs. On the other hand I have some 450V chips in my Paradox SE 300B prototypes. They load the hybrid shunt regulator that regulates the C4S'd driver tube. They have held up just fine for three years now. I will also note that PJ worked out a way to use the C4S in that position instead, and that is what is employed in the Paramount. A lot of folks use the IXYS chips quite successfully on lower current applications.
    - Re: C4S performance vs voltage drop - DHT 4 ME 12:57:57 04/07/06 (0)
      Thanks DOC
      Bob

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