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vintage tube valve crystal wireless museum DE5 detector special 5 modern wireless john scott-taggard

This is the 'Special 5' designed by Percy W. Harris M.I.R.E. The design, for home construction, was published in Modern Wireless Vol. V, No. 2 in November 1925 (with a follow-up article one month later). There was certainly no shortage of projects for the home constructor in 1925. The November 1925 issue of Modern Wireless featured no less than 5 receiver designs plus an audio amplifier.

This example of the 'Special 5'has been well made and is housed in a polished mahogany cabinet with a hinged lid. Reproduced below is an advertisement for the components necessary to construct this receiver which appeared in the same issue of Modern Wireless.

The total cost of components in the advertisement is £14 13s 5d but this did not include valves (say another £3) or batteries (perhaps £2 12s) making a total outlay of £20 5s 5d (£20.27 or 29.40USD). This would have been a considerable expenditure in 1925, affordable only by the 'well heeled'.

Below is reproduced the circuit of the 'Special 5'.

The circuit of this TRF receiver uses 'neutralising' condensers to control the amount of positive feedback (reaction) and so affect the sharpness of tuning and sensitivity. These 'neutralising' condensers were adjusted so that the set did not quite oscillate over the full range of the tuning condensers. The 3 tuning, 2 reaction and 3 filament controls must have made it quite difficult to adjust. The valves used in my example are type DE5.