7f33ac1a_ecp_cc__Value_Notes
[Part] C2L, C2R [Size/#] 10.5mm case, 5mm pin [Value/Notes] 
These are the tube's cathode bypass capacitors. You may be able to leave them out -- doing so increases plate resistance and distortion (mostly 2nd harmonic) and reduces gain, some people find it sounds better in some circuits -- otherwise they should be sized for a decent 3dB point. To determine this, you must consider what resistance the capacitor sees. Generally, you would consider the plate resistance of the tube + the plate load resistor, divided by the mu of the tube (plus 1) all in parallel with the cathode bias resistor. However, since the plate load of the tube is a CCS and is thus, for purposes here, infinite, the math becomes a lot easier. You only need to consider the cathode resistor. To know what that resistor will be, you will need to do a little math, but since we are planning to drop in the range of ~1V at between 1 and 3mA, the worst case is that the resistor will be in the 300R range. A 100uF cap would thus be sufficient. So, use a 220uF cap or larger and forget about it. The formula for figureing out what cap size to use for a given resistance is given here. These caps will only see a couple of volts, so large voltage caps are unnecessary. owever, they are directly in the signal path, so quality counts.
ecp.cc
Value/Notes