I have a Silvertone 1483 that I replaced the 6L6's with 6V6's for a lower volume around the house. Do I need to change the impedance of the speaker? Stock the amp is a 2 6L6 30W, only running about 350V on the plates and an 8ohm speaker. I do not believe there is a second tap on the OT, but I'm not 100% positive as I am relatively new to reading schematics. Thoughts?