All triode tube units will present a capacitance at the input, if the gain stage is a simple common cathode topology. This is due to capacitance between the anode and grid, primarily, and to a lesser capacitance between the grid and cathode. This is called Miller capacitance. The 12AX7 has very high miller capacitance owing to its high gain factor. So add 50 to 100pF to whatever you think is cable capacitance. A cascode at the input avoids miller capacitance, but usually you won’t have a 12AX7 in a cascode. Transistors and op amps exhibit a similar phenomenon.
Jolida JD-9 Upgrade
I've had my Jolida JD-9 phono stage for over 20 years, and it's been even longer since it had its Level 3 upgrade done by PCX. Is there a time when it needs the opamps, caps, etc., replaced short of failure? Nothing lasts forever, and I haven't noticed any change in performance. If it needs it again I'm going the DIY route.
Thanks,
John Cotner
New Ulm, MN