Amp: Echo Twin 45 (60's clone of a Super Reverb) Tube numbers are written next to the sockets. From left to right (starting next to the powertube): 12AT7 6AQ8 12AX7 12AX7 (I think) 12AX7 These are the tubes I have: Ruby 12AX7 Svetlana (I don't know what it is...the rest is worn off) Unmarked tube RCA ECC85/6AQ8 JAN Phillips 5814A (12AU7?) I also have a JJ ECC83S that I'm going to use in the first 12AX7 socket (all the way to the right). The owner told me that the socket next to the power tube is the phase inverter and you should use a 12AT7. I don't know which tube is a 12AT7 though. The socket next to that is for the reverb/trem...he said I should use a 12AU7 (this socket has 6AQ8 written next to it). I've noticed that the JJ ECC83S, the Ruby, and the unmarked ones are all the same size and bigger than the Svetlana, RCA, and JAN. Are 12AX7's physically larger than lower gain tubes, or does actual tube size just vary by manufactuer? Any other input? Also, the voltage switch on the amp has an option of 100 volts or 117 volts. Which one should I use?