• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Diy 100W Tube Amp Output Transformer

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#23
Christian Steyn said:
The program said: 1743 turns on the primary (0.28mm diameter wire) & 76 turns on the secondary (0.5mm diameter wire). I checked and these results do get the impedance ratio right. How does this sound, right or wrong?

Once more, thanks all.
Click to expand...

The screenshot shows much thicker wire (0.62 computed) than you actually use (0.28). The thin wire will fit, but is too thin for the required current. Using the thicker wire will overfill the bobbin, so you will need to reduce the number of turns, hence lower inductance resulting in less bass response.
The same goes for the secondary (actual 0.5 instead of the calculated 0.89).
You can reduce the insulation between windings to win some space for more turns/thicker wire, at the cost of high frequency response.
Play with the program to get a feel of the effect of each parameter.
 
#24
Parafeed813 said:
The screenshot shows much thicker wire (0.62 computed) than you actually use (0.28). The thin wire will fit, but is too thin for the required current. Using the thicker wire will overfill the bobbin, so you will need to reduce the number of turns, hence lower inductance resulting in less bass response.
The same goes for the secondary (actual 0.5 instead of the calculated 0.89).
You can reduce the insulation between windings to win some space for more turns/thicker wire, at the cost of high frequency response.
Play with the program to get a feel of the effect of each parameter.
Click to expand...

0.62 mm thick wire would be like a 22AWG thats good for 1A at almost 2A/mm^2 current density, 0.28 mm would be like a 30AWG wire good for 150 mA for the same
current density.
The 0.28mm diameter wire is a bit thin for the transformer primary but its not so critical, a 28AWG would be better for a 200mA biasing, also would reduce the winding DCR
 
Last edited:
#26
Thanks again maton00, I fixed the wire thickness (that could've been a massive balls-up) and Parafeed813, I think I'll need to use a bigger core anyway (Classic Tone 40-18013 specs say about 10x10x12cm) wich would solve the space issue of the windings. I might even use slightly thicker wire just to be safe.

Also: does anyone have any ideas about where I could get a 10x10x12cm core? preferably that i can salvage from something? I have a couple of old transformers and large motors that I salvaged laying around but nothing that big.

Thanks all.
 
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