My main amp is a DIY 300B, the input stage is a WE437@ but instead of a grid leak (which is a resistor to ground before the input tube), I'm using a grid choke instead, no coupling cap and inline grid stopper of 100 ohms. The DCR of the grid choke is 1.3K ohm, but it's AC impedance is 500 Meg ohm. I'm using a modified Dahlquist Low pass active, high pass passive crossover. If I use 1.3K the calcs say if I use a 1.5uf cap, my freq of roll off is just a tick over 80hz. I assume it's the DCR that needs to be used in this case, rather than a conventional "input impedance, as I have no way of physically measuring it, and there are no "specs" for this DIY amp