poor man's tube circuit PSU transformers

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MaxDM

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Oct 23, 2018
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I once built a power supply for a microphone using two 230VAC to 12 VAC transformers, or something close to that.

The first, connected to the mains AC socket fed the heater supply voltage rectifier, as well as the secondary of the second transformer, which I wired backwards, to get 220 VAC. The second transformer was smaller than the first.

Worked fine, and it was relatively cheap.

Not sure about high-current circuits, though.

Both transformers were toroidal. I don't know if that makes any difference when wiring up a transformer backwards.
 
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ruffrecords

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Nov 10, 2006
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This is a well known and perfectly satisfactory technique if the exact transformer you need is not available. Transformers don't know they have primary and secondary windings, they just obey the laws of physics.

Cheers

ian
 

Rob Flinn

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Jun 3, 2004
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Sussex, UK
There a some very cheap options available if you look for R core transfomers on ebay. I have had good results with them & they can be cheaper than using 2 transformers in the way you are describing.
 

Tubetec

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Nov 18, 2015
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3,110
Shaver socket transformer has 110/230 output tappings and plenty enough current for a tube mic anode or small preamp , usually available off the shelf in almost any hardware store .

The Farnell transformer appears to bring all four windings out seperately which makes it a bit more usefull than the shaver socket variety.

Ive tried the back to back transformer setup a few times for small low current supplies , it does work but I prefer to seperate HT and LT supplies from the ground up if using two transformers .

One of the handy things about back to back transformers is you can easily make any combination of voltages you need , for instance lets say you need 9volts ac to create a regulated heater you can use an 18 volt transformer for the step up side to get around 110v ac . I'd avoid going the other direction and energising whats usually a 6 volt winding with 9 or 12 volts though as the transformer will run hot and possibly vibrate and create other electrical noises .
 
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