I just got a 1965 Fender Tremolux and would like to use an extenstion cab. What is the correct impedance? I have a 4 ohm Mather 2x10 cab that I'm hoping to use. Dumb question, what happens when the "load" isn't correct? Thanks!

The impedance the amp "wants" to see should be printed near the speaker jack. 4 ohms is correct for a '65 Tremolux. http://ampwares.com/amplifiers/fender-blackface-tremolux/

Thanks for the information. I think that part of my confusion is that if I use both the internal speaker out and the external speaker, what should the total load be? If both are 8 ohms then in parallel the total is 4 as you mention? Which means when you don't use the extenal speaker out the load is 8 and that is also OK? Does that mean that amplifers can handle a "range" rather than one specific load? Thanks.