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Re plate or cathode resistors

Posted by Lew (A) on December 27, 2005 at 08:41:55

In Reply to: Re: DIY posted by hitsware on December 23, 2005 at 07:45:00:

Thank you for pointing out the errors in my thinking. Tubes can fail in either mode, as an open or closed circuit, but that does not usually happen except that the 6AS7 has an internal fuse which can blow and give you an "open", in which case one would measure no current across its plate (or cathode) resistor. With regard to my statement about what you would see if you measure V across one of the plate or cathode Rs in the case where the tube is functional, Thievenen's (sp?) Law would suggest you are correct.

The reason for the introduction of the plate or cathode resistors in the Atma-sphere circlotron was indeed to equalize the current draw for each tube under dynamic conditions. One might argue that the very low value of the R used (don't remember but ca one ohm) would not be sufficient to have a significant effect on this phenomenon, given that each tube has a plate resistance of (don't know for a 6AS7, but greater than 100 ohms). I have no opinion because I have never installed this option into my Atma-sphere MA240s which use 6C33C output tubes.

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