6x12's at 12ohms? Advice

[xjbear]

I'm running 2 6x12's loaded with 16 ohm celestions. Total impedance is 12 ohms per cab paralleled to 6 ohms together when plugged into my Model T.
My question is if running at 12 ohms am I better off setting the amp for 8 or 16ohms? And what the drawbacks? Same with when running both cabs ill have 6 ohms, is it better to set the amp for 8 or 4 ohms? And why?
I would assume to always opt for the higher setting on the amp to stress the ot less but im not sure.
Thanks for any clarification,
Bear

[cooldude666]

Think about how an output transformer works and the answer should come to you. OTimpedance is a wealth of information on the subject.

It's a difficult question to answer properly without transformer specs. Generally you should go lower, as increasing the reflected impedance is more likely to cause issue than decreasing it is. Read that aikenamps article carefully and you should have a much better understanding. Report back if you need things cleared up after reading the article twice. Good luck. Which model T are you running?

[J M Fahey]

Without measuring I'd rather go up than down (i.e. hooking it to the 8 ohms tap) because it's easier on tubes (specially modern or worn ones), but the best way is to setup a load resistor, generator and scope and *measure* power output when *just* clipping.

Surprisingly there won't (or shouldn't) be that much difference, but anyway the one that provides most clean power is, by definition, the best of them.

Nothing beats actual measuring

[Chuck H]

we covered another issue on the subject here:

http://music-electronics-forum.com/t33794/

Juan's advice still applies on how to determine the most appropriate OT secondary.