Hi all, I'm slowly putting ideas together for a huge bass amp using either six or eight 6550/kt88s. Having looked around there's not a lot of choice for output transformers on this scale so I've found a UK company that can wind them for me at a reasonable price. What I need to know is how do I calculate the required input impedance required for these or any other valves used in large numbers? If I double the number valves do I simply halve the impedance? Any help is greatly appreciated.

Thanks for reading, cheers Just