This download covers the construction of a three-valve radio receiver built using old-fashioned methods of a neat layout on a polished wood baseboard with plenty of brass-work. It covers the medium waveband, and is powered by modern batteries. The bulk of the components are readily available, and small RF chokes of modern manufacture are used in place of hard-to-find coils.
Probably, the most elusive and expensive parts are the three valves: SG215, HL2 and KT2. These often turn up on Ebay, or may be obtained from vintage valve suppliers such as Langrex, but they can be quite expensive. With this in mind, I have also shown that more modern valves will work just as well, namely two 1T4 pentodes and one DL96 beam tetrode. These are still quite easy to obtain at much less cost than the vintage types. A description of how to construct adapters to use the cheaper 1T4 and DL96 valves is included in the document. Other two-volt types will usually work to a greater or lesser degree.
I have assumed a general knowledge of radio, and home construction, such as soldering, and simple wood and metal work. This circuit was developed by myself over several weeks of experimentation, trial and error. I have not gone into the theory of how it works, as this is basically an exercise in home construction in the old style.
The valve filaments are supplied by a two-volt re-chargeable sealed lead acid battery that I obtained from Ebay. They are generally used in radio control models. The high tension supply can be obtained by clipping a number of small 9 Volt batteries back-to-back to obtain the required 100 Volts. I find that 9 batteries will supply the 100 Volts, because new ones are usually slightly above 9 Volts! I obtain them from the wide-spread "pound" shops that can supply a pack of three for £1.
The 100 Volts is not dangerous, but you may experience a "tingle" if you touch the total of 100 Volts with wet hands. It is best to assume that it is dangerous, and be very careful not to accidentally connect yourself to it!
A good aerial and earth are also required. The aerial may be a length of thin insulated stranded wire trapped in the window frame and extended to a tree, or nearby building such as a garage roof. The earth can be a copper rod knocked into the ground just outside the window, with the lead-in trapped in the lower window frame in a similar manner to the aerial. The receiver drives a loudspeaker at more than adequate volume.
If for some reason, the download does not go through OK, please e-mail me at mailto:firstname.lastname@example.org and I will send a direct download link.
Robert A. Wilson
8th August, 2016