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RE: Cathode bypass cap removed and I like it

Posted by dave slagle on January 11, 2017 at 06:52:41:
OK.

I am not intimately familiar with the ESL63 but in general an ESL panel is a pure capacitance and the thing that makes them "difficult to drive" is actually a function of the step up transformer and the crossover that follows it. By removing the cathode bypass you have dramatically altered the behavior of the tube essentially increasing the RP from about 800 ohms to about 6K. This means your output impedance is now probably greater than the load it is driving and interestingly enough, some speakers actually like this situation.

The logical thing to do would be to use a mic and take frequency response measurement sweeps with and without the bypass cap and see if anything jumps out at you. My first guess would be that you would attenuate the HF info because of the higher output impedance working against a fixed capacitance. Unfortunately the 63's have a delay line in addition to a crossover so I fear simple theory goes out the window.

dave