Supro preamp bias question

[phydauex]

Howdy All,
I'm working on an old Supro SE/ 8" speaker, not sure exactly which model it is. has three inputs, 12AX7/6V6 and 5Y3, and one Vol one Tone. Geting it up and running again, going to put in a ground plug and some minor other things to make it quieter/reliable. Main question is the first stage preamp uses 5meg resistor to ground off the grid (contact bias) and the cathode connected direct to ground. Someone along the way had also put a 47uf@25v cap from the cathode to ground across that wire? I believe that it's useless to bypass a wire with a cap. I'm not sure what they were thinking, unless I'm missing something. So, if I stick with the contact bias, I should remove the nonfunctioning cap or should I rewire this to a common Rk plus cap set up?
Matt

[Jazz P Bass]

Curious mod, for sure.

[phydauex]

Actually, I was erroneous before. Upon closer inspection with a flashlight, I see that the jumper goes across pins 3,9 with the cap from pin 3 to ground (this is a 12AX7). So the heater is actually grounded at that point.I've seen the chassis used as a return for the heater, but not two seperate heater lines then just attached to ground. In addition to the cap to ground there also. I don't know if someone thought they were going to get more gain from the preamp or it is to try and isolate the preamp cathode from the heater? Anyway, I'm going to seperate the heater from that and give it it's own ground point with a couple 100 ohm resistors.