OT Impedance

[minions]

Alright, I know we discussed this in this thread already:

guitarnuts2.proboards.com/index.cgi?board=Amps&action=display&thread=4905

But I just want to be 100% sure.

If I use an OT with a 4K input with two 6V6s, will the reflected output impedance be doubled or not?

[sumgai]

Doubled compared to what?

[minions]

Well the OT I'm looking at has a 4k input and 2, 4, and 8 ohm taps. So when used with two 6V6s, would these then become 4, 8, and 16 ohm taps?

[stevo58]

An output transformer's secondary impedance comes from the turn ratio, that is, the ratio of turns on the primary to the secondary.

So, if the primary side is 4K, and the secondary has 2, 4, and 8 ohm taps, then the turn ratios are:

4k/2 = 2000
4k/4 = 1000
4k/8 = 500

The transformer is reflecting the nominal impedance of the speaker back to the tubes.

So if you plug an 8 ohm speaker into the 2,4,and 8 ohm taps, the reflected impedance would be:

8 ohm into 8 ohm tap = 8 * 500 = 4K
8 into 4 = 8 * 1000 = 8K
8 into 2 = 8 * 2000 = 16K

6V6 guitar amps (by which I mean the tweed deluxe and the BF deluxe) are set up for either an 8K primary impedance (tweed deluxe) or a 6.6K primary impedance (BF deluxe).

So if you wanted an 8K primary impedance with an 8 ohm speaker with that transformer, plug it into the 4ohm (1000) tap.

If you want a 6.6K impedance, still use the four ohm tap. 6.6K is close enough.

So, the answer to your question is yes, as far as you are concerned.

steven

[minions]

Wow, that was very enlightening

Thanks steven!

I was always under the impression that an 8 ohm speaker had to go into an 8 ohm secondary. Good to know.

Apr 29, 2010 5:37:49 GMT -5 stevo58 said:

So, the answer to your question is yes, as far as you are concerned.

Wait, yes what? Would the taps (2, 4, 8 ohm) be doubled with 6V6s (to 4, 8, 16 ohm)?

[minions]

Okay never mind, I read through your post again, and I get it now. Thanks!