Which of these output tubes?

[jnb]

For a tweeter, would you choose a 45 or a KT66?

For a woofer, would you choose a KT66 or a 6550?

All single ended, power output not an issue.

 

[kevinkr]

I think it depends mainly on how much output power you require.

The 45 in SE is good for no more than 2W, the KT66 probably around 5W - 6W, and the 6550 perhaps 7W - 10W in triode connection.

Another option for the tweeter amplifier would be the 2A3 which could get you to 3.5W output.