Parmeko transformer question...

[dondnile]

Hello Experts...

A while back, on a trip to England, I came accross a couple of Parmeko Transformers. I am building a lower power Marshall/Bassman amp to try one out.

The output has:

Pin1 Pin2 Pin3 Pin4

and states: For 3.75 ohms, Connect Pin1-Pin3, Pin2-Pin4, Ouput Pin1 and Pin2

For 15.75 ohms, Connect Pin2-Pin3, Outputs Pin1 and Pin4

Does this mean there are 2 8-ohm windings Pin1-Pin2 and Pin3-Pin4?

For 8 ohms, if I just connect a speaker to Pin1-Pin2, is the other winding open and will it fail under the open load?

What is the best way to connect the outputs?

Thanks so much in advance...

[Phil_S]

I think you will need to test the OT to be certain and I'd be careful not to jump to any conclusions. It's all in the math. The turns ratio is the square root of the impedance ratio. Let's assume you have an 8K primary.
8000:4 = 500; sqrt(500) = 44 turns
8000:8 = 1000; sqrt(1000) = 33 turns
8000:16 = 2000; sqrt(2000) = 22 turns
I rounded some to make this simple

Use a low a/c voltage source. A 6.3V or 5V filament transformer is good. You can use the filament winding from any PT. Apply the low voltage to the secondary, let's assume 5VAC here. On the 4z output, the primary will read 44*5 = 220VAC; on the 8z, you'll get 165VAC; on the 16z you'll get 110VAC.

Adjust all the math to the specifics of your OT.

[martin manning]

The output has: Pin1 Pin2 Pin3 Pin4

and states: For 3.75 ohms, Connect Pin1-Pin3, Pin2-Pin4, Ouput Pin1 and Pin2

For 15.75 ohms, Connect Pin2-Pin3, Outputs Pin1 and Pin4

Does this mean there are 2 8-ohm windings Pin1-Pin2 and Pin3-Pin4?

No, you have two ~4-ohm windings. If you parallel them you still get ~4 ohms. If you connect them in series you cut the turns ratio in half, and therefore decrease the impedance ratio by the square of 1/2, which is 1/4, making it a ~16-ohm secondary.

[dondnile]

Thank you Martin and Phil for replying. I think what I will do for the mean time is wire it up as 16 ohms and just use a 16ohm 12 or a 4x12 cabinet. I have a 55W 20ohm resistor I wanted to wire as a safety load and for slaving the amp. This will work out just fine.

I was just wondering if there was a way to wire it up 8 ohms, but it doesn't seem like it and I don't want to risk burning the windings.

Thanks for the help..... I'll post picutes when its all done.