I recently sold my 502p…a great amp that served me well for years. The 12AX7s are on the "inside" of the small tube pairs. I had a "Littlite" gooseneck light over the amp that I would hang the bias meter cables over to keep them under control when using the meter to check the bias, but burning my fingers was part of the ritual…however, the bias LEDs were very accurate and I didn't really need the meter.
jolida 502b manual bias adjustment
owners of the jolida jd 502b, how you set the bias manually without losing all the skin on your hands? i'm lucky mine has the ez bias as well as the manual bias.