I got a new OT. Multipule questions.

[jimmybjj]

I have a champ aa764 circuit that I've installed a 6l6 in. I got a Hammond 125ese to try and take full advantage of having a larger tube in there. I am still unsure about OT's. I understand the OT is kinda like a bridge between the power tube and the speaker. What i don't understand is the impedance relationships and when to use what as far as taps go. The 125ese has 2,500/10,000 primary, this confuses me, is the transformer only capable of translating the 2500/10000 impedance to the power tube? If that is true, will this transformer not work for a 6l6, average load resistance of 5000ohms. Which secondary tap should I use for a 8 ohm speaker and the 6l6? It seems the more i read about this, the more confused i get. Thanks for any guidance and/or advise.

[Geezer]

On that OT chart, don't worry about the numbers on the left-hand side (primary).....it's just telling you the "range" of primary imp's available.

Look at the right-hand (secondary) chart #'s.

Each tap (secondary wire) has a list of choices.
1st determine what speaker imp you are using....let's say you have an 8Ω speaker.
Now, you determine which tube you are using (6L6) & what primary imp it "likes" (as you said, ~~5k)

So, look at the chart for an 8Ω load with a 5K (5000, or something close to that) directly underneath it.

The yellow tap has an 8Ω with the # 5000 under it..........so that's the tap you use.

IF you had a 6V6 (wanting a 10k primary) with the same 8Ω speaker, then you would use the Green tap....see the system?

HTH, Geezer

[tubesornothing]

Another way to look at it:  transformers are ratio device.  Its  a way of converting high voltage to low voltage or high impedance to low impedance.

All they are saying is: the ratio between input and output stays constant, so you set the primary load by putting on a different load of speaker.

if you attached a 8ohm speaker to the white wire, you will have a 2500ohm primary load.  2500/8  = 312.
if you attached a 16ohm speaker to the white wire, you will have a 5000ohm primary load.  5000/16  = 312.

Select a different winding, you get a different ratio.

So... like geezer says: pick your primary impedance based on the power tube (say 10k) and you have an 8ohm speaker in the box:  then select black and green taps for the secondary.

[jimmybjj]

thanks guys, things are a whole lot more clear now.