I've been given some small output transformers which supposedly came from an old single ended amp.
There are no markings on the transformer to give any clues as to what i could use them for.
One winding measures zero ohms and the other 340 ohms. Both transformers are identical.
Does anyone have a clue what they might be, or which valves they could be used with?
Thanks in advance.
There are no markings on the transformer to give any clues as to what i could use them for.
One winding measures zero ohms and the other 340 ohms. Both transformers are identical.
Does anyone have a clue what they might be, or which valves they could be used with?
Thanks in advance.
Hmm...although Output transformers they are still transformers, and through voltage ratios you can calculate impedance ratios.
The DC resistance values you measure for the windings can be about right: one high value and one low value. Off course if the resistance is truly zero the winding is probably shorted and the trafo's can be thrown away, but probably it is CLOSE to zero, what is perfectly normal.
You already did the first step, identifying the windings as the primary (the 340 ohms one) or secondary (the 0 ohms one). To calculate the voltage ratios you should appy a voltage to one of the windings. I think the best is to apply about 50VAC (best is to use a variac and slowly turning voltage up) on the 340 ohms one. NOTE: DON't APPLY 50VAC ON THE ZERO OHMS ONE!! With 50VAC applied measure the voltage on the secondary. It should be some volts, maybe between 1 and 2. Measure carefully (with all comma's behind zero). Now divide the exact voltage on the primary through the exact voltage on the secondary: you have got the ratio. Square this value and multiply it through the load you will put on the secondary, let's say 8 ohms. The value you obtain is the reflected impedance on the primary.
If the trafo's are small i would use them for up to 40mA of current through the primary. More current may damage the wire and/or cause saturation of the core.
Erik
The DC resistance values you measure for the windings can be about right: one high value and one low value. Off course if the resistance is truly zero the winding is probably shorted and the trafo's can be thrown away, but probably it is CLOSE to zero, what is perfectly normal.
You already did the first step, identifying the windings as the primary (the 340 ohms one) or secondary (the 0 ohms one). To calculate the voltage ratios you should appy a voltage to one of the windings. I think the best is to apply about 50VAC (best is to use a variac and slowly turning voltage up) on the 340 ohms one. NOTE: DON't APPLY 50VAC ON THE ZERO OHMS ONE!! With 50VAC applied measure the voltage on the secondary. It should be some volts, maybe between 1 and 2. Measure carefully (with all comma's behind zero). Now divide the exact voltage on the primary through the exact voltage on the secondary: you have got the ratio. Square this value and multiply it through the load you will put on the secondary, let's say 8 ohms. The value you obtain is the reflected impedance on the primary.
If the trafo's are small i would use them for up to 40mA of current through the primary. More current may damage the wire and/or cause saturation of the core.
Erik
I use opposite approach. Connect the secondary to the output of the SS amp through 8 Ohm resistor, put 41 Hz on input of the amp, an oscilloscope on the primary of the tranny(with 1:10 probe!), and slowly increase the volume untill you see the tranny starts to saturate. Measure ac on the secondary, it is the maximum voltage it can give on output tabs. Now, multiply resistance of primary by 10 to get impedance with 10 percent loss, and calculate nominal output impedance using the ratio measured by the same oscilloscope, dividing voltage on primary by voltage on secondary (don't forget about square for impedances). Now, increase output impedance up to one of standard values (4, 6, 8, 12, 16 Ohm) and recalculate impedance on the primary.
It is approximate method, but it works well. Sometimes vintage transforfmers were designed to work from 63 Hz or higher, so you may get less power handling that it was intended for, but with better sonical results.
--Anatoliy
It is approximate method, but it works well. Sometimes vintage transforfmers were designed to work from 63 Hz or higher, so you may get less power handling that it was intended for, but with better sonical results.
--Anatoliy
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