This is something that I always wanted to do, to come up with my own transformer design. Well, I did have help. I designed what I would like in a holy grail crystal radio transformer and a major transformer manufacturer did the work.

While the Bogen T725 transformer is a good one for many medium performance crystal sets, it doesn't bring out the best in a high performance set. The Bogen, with it's 45k ohm tap, provides a great match to smaller strand count litz sets. But how about the sets that use 165/46 litz and up? A transformer with a 200k ohm primary will provide a better match to these tank cirucits.

How about a transformer (actually an auto transformer) that is made especially for the high performance crystal radio builder? I started with a wish list. To keep the expenses down, I spec'ed this transformer to provide a good cost vs. performance ratio. (Biggest bang for the buck). Here is what I came up with:

The transformer has to have a decent amount of iron in it's core. The more iron, the better the transformer will work, especially when the match isn't perfect. Larger wire can be used, compared to those tiny transformers you see around. This keeps the copper losses low. So a transformer with a Bogen like core was selected.

I asked the maker to allow for dc bias of at least 1 ma. This means that this transformer can be also used as an audio choke or audio auto former in a regen receiver (Doerle type for example). This provides for an additional use. An autoformer with a 4.5:1 transformation ratio.

The highest tap impedance is 200,000 ohms. Think of how much less loading this will be on the tank. Higher selectivity is assured, as well as a good power transfer with high efficiency.

The 5 other taps were selected by thinking how a crystal set builder might use the transformer. The output taps are for different kinds of earphones. The 10k ohm tap is for crystal and piezo earphones. The 5k and 2.5k ohm taps are perfect for magnetic headphones. The 1.2k tap is also useful for sound powered phones with the elements wired in series. The 600 ohm is great for parallel wired sound powered phones.

Here is a little project that I made with the Überformer. I call it the ÜberMatch. I don't sell the ÜberMatch, but project is something that is easily built. It allows you to buy just one Überformer and move it from one radio to another.

So, to review, this transformer (which I call the Überformer Model XTAL200K) has a 200k ohm input with a 10k, 5k, 2.5k, 1.2k and 600 ohm taps for the output connections.

Interested? You probably want to know how much and when can you get it? The transformers are $35 each. The supply is limited to what I have on hand. They are available now!

Please go to my main ordering page and put yours on order.