DB, after checking further I found the following quotes from John Curl, the very distinguished designer who as you are undoubtedly aware did the electrical design of the JC-3. The quotes appear on pages 3953 and 3956 of this thread:
-- Al
There is a 100pf cap at the input to ground for the JC-3. Some criticism has made me now wonder if 50 pf might be better?Best regards,
... My best guess at this time [May 20, 2013] is that the effective input capacitance of the JC-3 is 125pf or slightly less. I could drop that in half, and I might, in future. The potential advantage may not be worth much. I will think about it.
-- Al