Connect a resistor (say 220R 5w) across any two of the secondary wires. Connect an AC voltage to the primary (240v would be OK as long as you're CAREFUL and use an isolation transformer), and measure the output voltage at each secondary wire. The 8 ohm tap voltage will be twice the 4 ohm tap voltage, and the 16 ohm tap voltage will be twice the 8 ohm tap voltage.
A little experimentation will determine which is the common (only one wire will produce 3 increasing voltages in a 1:2:4 ratio on the other three wires.)
Ive found a spare Output TX in my box - T125 - which I think was a magic parts Bassman replacement TX i bought years ago.
But Ive lost the color codes for the secondary wiring.
i THINK it is :
Black - ground
Green - 2 ohm
Yellow - 4 ohm
Orange - 8 ohm
but I'm by no means certain
Can anyone clarify for me ??
If they are drop in replacements - what are the standard Fender color codes ?
Cant find anything by Googling, or looking at Magic Parts site.
Help !!!
Thansk
Pete c
i've used these a couple times yrs ago and i think the orange tap is the 2 ohm tap. not sure about the order of the others but i think the green is 4 and yellow is 8. rh
novosibir wrote:
Mark, I hate to correct you, but:
No you don't!
Actually, the original question was 2,4,8 (my bad).
novosibir wrote:
- on the 8 ohms tap will be 1.41 the voltage of the 4 ohms tap
- on the 16 ohms tap will be twice the 4 ohms tap's voltage
I think you're right; Transformers always cross me up, since Ohm's law doesn't directly apply. Of course the V x I product should be the same on each output tap, so using 10v on the 2-ohm tap (to make the math easy):
10v on 2 ohm
14.1v on 4 ohm
20v on 8 ohm
10 x 10 / 2 = 50w
14.1 x 14.1 / 4 = 50w
20 x 20 / 8 = 50w
Can we talk some more about this Larry? There are certain ratios that come up all the time in electricity. 1.73 for instance is the vector sum of two voltages 120 degrees apart. That one's real easy for me because I can draw the vector with a pencil and paper. 1.41 is more or less the square root of 2. It's the ratio between peak and RMS power I think, amongst other things. Here it shows up again.
We know that: turns ratio squared is the impedance reflected back to the tube from the speaker output. So, a 1:33 turns ratio with an 8 ohm speaker tap yields approximately 8.7K primary impedance. So.....if I put 100 volts on the primary of this transformer I should see 3.03 volts on the 8 ohm tap. Now I think you're telling me that the turns ratio on the 4 ohm tap will be 33 multiplied by 1.41, or 46.53 while the 16 ohm tap will be 46.53/2 or 23.27?
It's painful for me to admit, but I just don't get what the square root of 2 has to do with one multiple of output impedance while the simple multiple of 2 solves the other. It has to have something to do with squaring the turns ratio but why doesn't it go 2.82?
Signed: the math wimp.
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Well, I'm not Larry, but...
If the first voltage is unity (for sake of argument),
The second (twice the impedance) is SQRT(2) bigger = 1.414
The third (four times the impedance) is SQRT(4) bigger = 2
The third is also twice the second, SQRT(2) x 1.414 = 2, same result
