The MiniBlok SET Amp

Posted on Feb 7, 2014

This project uses just one tube. However, the tube chosen (13EM7) actually contains two separate triode structures. One is physically quite small, and is capable of a large signal gain but little power. It therefore makes an ideal preamplifier stage. The other section is larger, and ha

The MiniBlok SET Amp
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s a lower voltage gain, but is capable of a significant amount of current. It therefore can deliver up to about two watts of power into a speaker load under the appropriate conditions. This tube was originally designed to be used in television sets. The small, high-gain section was typically used as the vertical oscillator, and the larger section as the vertical output stage. However, it also makes a splendid audio tube. If you think about it, linearity is no less critical in television sets than it is in high-fidelity audio. At the same time, there isn`t the "mystique" around television tubes that there is around so-called "audio" devices, so the price is a lot more reasonable than otherwise quite similar tubes such as, say, the Type 45. There are a few different variants of this tube which can be used. The 13EM7/15EA7 is functionally identical to the plain 13EM7. If you`re buying a tube for this project, either variant will be fine. If you have a "junk box" of tubes, but don`t have a 13EM7, you might have a look to see if you can find a 10EM7. This is the same tube, but with a lower-voltage filament. It can be used in this design if a filament dropping resistor is added (details later). The 6EM7 or 6EM7/6EA7 could conceivably be used also, but will be a bit more involved; for this reason this option is suggested only for more experienced tube equipment builders. Similarly, there are other tubes such as 13FM7 which would...

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