07-25-2014, 06:01 PM
(07-23-2014, 04:44 PM)Denton Wrote: So Hangman.. What if I just pulled two power tubes to drop it to 60 watts across the 2 C Rex's?
Which two are the pairs? Two inners and two outers? Also, they are two 8ohm speakers - so wired to 4 ohms. Is it increase to 8 or drop to 2 ohm when pulling the tubes?
For simplicity's sake lets say remove either the inner or outer pair. Technically you could do other combinations, but by making things complicated the opportunity for mistakes or misunderstanding is higher.
If you have two 8ohm speakers in parallel, your speaker load is 4ohms, but when you pull two tubes the primary impedance doubles. So we have a situation where the secondary is staying the same but the primary is changed.
Let's pretend that the primary impedance is 1.6k with all of the tubes in there, At 4ohms the impedance ratio is 400/1. At 2 ohms the ratio is 800/1
When we pull two tubes then the primary impedance is 3.2k.
3.2k/4 = 800
So we need an impedance ratio of 800/1
That is the ratio we have when the impedance selectors is set to 2ohms
So set it to 2 ohms