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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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1st Sep 2015, 2:25 pm | #1 |
Pentode
Join Date: Jul 2014
Location: Bangalore, India
Posts: 132
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Crystal Radio Output Transformer
The large size of the power transformer, used as an output transformer for my Loudspeaking Crystal Radio, was good enough reason to attempt homebrewing a relatively small one.
A search through the junk box yielded a 47mm diameter, Siemens N22 pot core set. https://www.vintage-radio.net/forum/...1&d=1441113729 Winding was for an autotransformer, having 500 turns (the maximum number that could be accomodated) of 30 SWG enamelled copper wire, with output taps at 50 and 100 turns. https://www.vintage-radio.net/forum/...1&d=1441113829 The 50-turn tap was to match the existing 3 Ω speaker and the100-turn one a provision for speakers of higher impedance. A small PCB, also from the junk box, provided termination points for the winding. https://www.vintage-radio.net/forum/...1&d=1441113869 A couple of white plastic cosmetic jars were reworked to form the enclosure, giving the transformer a presentable appearance. https://www.vintage-radio.net/forum/...1&d=1441113902 Tests indicated that, for its size, the output transformer's performance is comparable, though not equal, to that of the power transformer. |
2nd Sep 2015, 3:49 pm | #2 |
Tetrode
Join Date: Mar 2010
Location: Monroe, Georgia, USA. (from Coventry, UK).
Posts: 77
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Re: Crystal Radio Output Transformer
Nice work!
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2nd Sep 2015, 7:23 pm | #3 |
Octode
Join Date: Jul 2011
Location: Leicester, Leics. UK.
Posts: 1,685
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Re: Crystal Radio Output Transformer
That's an interesting idea. I wonder if it can be adapted with different cores (are the pot cores the same thing as ferrite rods, and could one be wound on a ferrite aerial?). 500 turns isn't a lot. Eg for low impedance 'phones on a crystal set. Clearly the low number of turns doesn't impede the performance of your set - I wonder if more will be needed for a sensitive design, as i should think 2KOhms at least would be optimum.
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2nd Sep 2015, 8:57 pm | #4 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 14,007
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Re: Crystal Radio Output Transformer
In the past, when wanting to use low-impedance 'phones with a crystal-set I've used one of the little 'LT44' push-pull driver transformers.
Primary to the diode detector, then use half or all of the secondary to drive the 'phones - experiment with half- or full-secondary to get the best volume. |
5th Sep 2015, 6:57 am | #5 | |
Pentode
Join Date: Jul 2014
Location: Bangalore, India
Posts: 132
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Re: Crystal Radio Output Transformer
Yes, Tanuki, crystal radio is fun because of its endless variants!
Thanks, Colin! Quote:
The open magnetic path of a ferrite rod would increase the losses and result in an inefficient transformer. A ferrite E/I core would make a better replacement for the pot core. More turns with the same wire would increase the copper loss. Using thicker wire to counter that would result in a bigger transformer! Regards, Nandu. |
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7th Sep 2015, 10:05 pm | #6 |
Octode
Join Date: Jul 2011
Location: Leicester, Leics. UK.
Posts: 1,685
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Re: Crystal Radio Output Transformer
Thanks Nandu - a great deal of lateral thinking needed for crystal sets!
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15th Sep 2015, 7:19 pm | #7 |
Pentode
Join Date: Jul 2014
Location: Bangalore, India
Posts: 132
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Re: Crystal Radio Output Transformer
Anytime, Greenstar!
Regards, Nandu. |