FANCY DETECTOR CIRCUITS

Evening Post, Volume CX, Issue 68, 17 September 1925, Page 14

FANCY DETECTOR CIRCUITS

" Grid-Bias" ha* been asked from time tb time to advi*e oh the use of some special circuit, such a« the Cockaday or the. Reinartz. Now, both these, though very different in arrangement, are 'really simple regenerative circuits. The Cockaday is the old de Forest "ultraudion,"'the simplest of all the regensrative circuits .and a persistent oscillator, coupled to an absorbing circuit which takes away enough energy to stop .the oscillations."•" Theßeinartz is simply a plain ' three-coil regenerator with a fixed tickler containing a variable' reaction condenser. The steady plate current geos through a choke coil .to. the telephones or transformer following ih* valve, and the high-frequency waves in the plate circuit are allowed to pass to the required extent through the tickler; coil by means of the reaction condenser.' Such variations as these make the actual handling of the set a little different in each case, though after all there may be a good-deal of difference in the.be.haviour.of 1 two sets using exactly the same circuit. ;.Nevertheless, a regenerative set is a regenerative Viet j and, given qually good material and equally good workmanship and the game valve, the results, so far as sensitiveness is concerned, will be exactly similar. Ease of control does not depend '«> much on the circuit used (in a plain regenerative receiver) as upon' actual design; and selectivity depends mostly upon the inputj not' the output, circuit. / A feature of the standard Cockaday receiver is th*> coupling of the aerial circuit to; the, secondary by a single turn, phi*. th« effect of the aerial cbU itself, beings fixed t» the side of the secondary., Thi* give* pretty loose coupling and. high selectivity, but that is simply thereault of the loose coupling. ■ V :' > The moral of this k: if you h»v» a regenerative »et, don't rush into building another regenerative set' in the hop* that by some magic of a; new circuit it '■ will give better "results. Do it for furi; by all means ■ or do it if you think your next one will.be of better quality or more suited by its behaviour to your hands' and temperament. * As a matter of fact, many of the receivers that' have been putting ujj |world ; recordaj are'of excessive simplicity; they aire limple threecoil regerieratora,with no frills, and .ns-^ ually-with an untuned primary. ■