Jay, Using a single 4-125A, I obtained a 10" spark if I remember correctly. Using your two 4-65A's you might get the same spark length I suppose. Personally I prefer more powerful tubes for a VTTC. John -----Original Message----- From: jhowson4 <jhowson4@xxxxxxxxxxx> To: TCML tesla Coil Mailing List <tesla@xxxxxxxxxx> Sent: Sat, Mar 17, 2018 10:31 pm Subject: [TCML] VTTC tubes Hello all,With all the VTTC talk recwntly, I have been thinking. I have a pair of nos amperex 8165/4-65A tetrodes. http://www.relltubes.com/products/Electron-Tubes-Vacuum-Devices/Tetrode/4-65A-8165AM.htmlWhat are everyone's opinions regarding usage in a VTTC?-JaySent from my Verizon 4G LTE Smartphone _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxxxxxx https://www.pupman.com/mailman/listinfo/tesla