A recent PM made me realize that there is a lot of confusion about the parafeed capacitor value for the Stereomour (and Paramour). It has always been the same for the stock amp as shipped, but changes with different upgrade transformers and plate chokes. Here is the gist of what I replied; I hope it helps clarify the situation:
First, the voltage rating should be a minimum of 600v. We've never experienced any problems with 600v caps. I recommend a minimum 85 degree C temperature rating; some people have used lower ratings without problems but I still can't recommend doing so.
My rule for choosing parafeed caps is 2*L/(R*R) where L is the plate choke inductance in henries, and R is the output transformer nominal primary impedance in kOhms; the result is in microFarads, uF. Usually a range from half to twice that value will give pretty good results, and I've posted periodically about some considerations that might make one lean towards one end or the other. It is something of a compromise between small-signal bandwidth and power bandwidth.
A much smaller cap will reduce the bass extension. A much larger cap won't hurt anything; it is always at least equal to a series feed transformer with the plate choke's inductance.
Here are some examples:
Stereomour, stock iron, 2A3: 20 henries, 4Kohms, nominal 2.5uF, range 1.25 to 5uF (ships with 3.3uF)
Stereomour, stock iron, 45: 40 henries, 4Kohms, nominal 5uF, range 2.5 to 10uF (ships with 3.3uF)
Paramour I and II, stock iron: 10 henries, 4K ohms, nominal 1.25uF, range 0.625 to 2.5uF (actually shipped with 3.3uF for particular reasons)
Paramour I and II, earliest upgrade iron: 40 henries, 4Kohms, nominal 5uF, range 2.5 to 10uF
Paramour II, Magnequest upgrade iron: 40 henries, 3Kohms, nominal 9uF, range 4.5 to 18uF (recommended 10uF)
