From Radios to Amplifiers

From Radios to Amplifiers

A real boost came with a book about how to build a vacuum tube regenerative receiver. The circuits were powered by a AA and five to ten 9-volt batteries; and thus the fun continued. I continued to use vacuum tubes, and found a company where I could buy a 1H4 and a 1S4 to aid in my projects.

My foray into audio began when I discovered that my other grandfather had an old radio sitting on his shelf. When I asked him about it he told that me it was an old tube radio, a 1948 RCA 75X11, that had been given to him by a relative. I offered to repair it and he agreed to let me get it working again.

That took awhile. In the meantime I became interested in all manner of tube radios — I fear I could even be called a collector. Still, it was fun, and I still have a nice collection of gems from the olden days, most of which do indeed work. I won’t go into all the fun of finding these radios at antique stores (including my beloved Freed-Eisemann NR-5) nor the highlight of it all — the large sales along a certain highway in Kansas where two years in a row we made some nice “radio finds.” While it is true that on eBay you can find anything you want, these were certainly highly enjoyable times…you never knew what you might find!

Regardless, it was during all of this that I vaguely became aware of the better sound quality these tube radios had. At first I related the sound to the larger speakers, though my Philco Model 14 cathedral radio with its push-pull triode output stage sounds absolutely incredible.

At some point, I went back to The Boys’ Third Book of Radio and Electronics and there saw the plans for a simple audio tube amplifier using 12SQ7, 50L6, and 35Z5 tubes. I resolved to build it and use it to play music from an MP3 player. I didn’t go with the original design; a 35Z4 was just as good as the 35Z5 and cheaper, and a 14X7 would do instead of a 12SQ7. I obtained the 50L6 for $0.50 cents at a hamfest (talk about fun!) and built the project. This was the first audio amplifier I made.

As time went on I built a better one using some of the experience gleaned from studying tube radio schematics. My “better one” did indeed sound better and though very crude, marked the beginning of my interest in high-fi. I built a tube-based voltage regulator for it and used push-pull 6F6 pentode output stages. I presented it to my mother for Christmas, and that was that.

Thus far, aside from some tangential experiments I was still primarily interested in radios. That all changed, however, when I vowed to make my mother a better amplifier than my 6F6 job.

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