Its 4V, 0.9-1.2A heater tube with PX25 pins so adapter is needed...Romy the cat uses the YO 186 but I understand that is also from a cost perspective compared to telefunken
You think these will work with GG?
I asked Yoda about both RE604 and YO-186 and i got this response: "604 is like 242 heater but pinout has crossed legs i think; 186 is heated like px4 and has crossed legs as well; 300b base is ux4. Heater, heater, grid, anode. The 604 base is heater grid heater anode."
Based on this i abandoned YO-186/RE604 "project"