Laboratory Jottings

Radio Record, Volume IV, Issue 32, 20 February 1931, Page 30

Laboratory Jottings

"Colonial" Model 33 A.C. Feo Messrs, N. R, Cunningham, Lid, Masterton, we have received for test one of the new "Colonial" Radio Model 88 Receiver : Its distance-getting abilities certainly surprised us. Just before 10 o’clock one night, and a bad night at that, we went round the dial and counted 18 stations. Only five of these were New Zealand. They all came in fairly strongly, and could have been tuned in without any difficulty. In this ‘respect we would like to point out that when testing receivers we do not try for the maximum number of stations we can get with careful dialing. The station must be able to be tuned in fairly easily before we can count it "logged." This result is not, of course, intended to be the criterion of the set’s performance, but it gives some indication. of what it should do even under most adverse conditions, : ‘Selectivity is another strong feature of the set. We could separate 250 and 4QG from 2YA, leaving very little background, much less than our standard, and the excessive sidebands of 2YA, which in some receivers gives objJectonable buzz, are eliminated. Using the alternative aerial terminal selectivity was even sharper, but there was the concomitant drop in volume. Another remarkable feature of: this set is the volume control. Different from the usual screen-grid a.c, set, it was not necessary to remove the aerial to receive the local station; in fact, the set worked better with the aerial on. It has an almost perfect volume control, which operates on the r.f.. coupling and not upon the gridbias voltage of the screen grid valves. iIt-is for this reason that the volume control is so smooth. Another interesting and novel feature of the set is the automatic coupling. In the usual construction the coupling in the radio frequency stages is fixed, which frequently gives maximum sensitivity only at the lower readings of the dial. In the "Colonial," however, maximum sensitivity is obtained throughout the whole scale by means of an arrangement whereby the radio frequency coupling is automatically increased as the dial is turned to the higher wave-lengths. This is the only set we know of which incorporates this feature. The dynamic speaker, too, is unusual in that it has a 14-watt field coil. This extremely powerful magnetic field permits the use of a heavy ridged cone with a somewhat more stiff movement than is common, and this gives exceptionally good high frequency response. Due also to its heavy construction, the speaker will handle tremendous volume without showing any signs of distress. Pickup terminals are incorporated, and the changeover from radio to gramophone is accomplished by turning the dial round to the "phono" position. Because of this changeover switch, the pickup may be left connected when operating on radio. The fidelity of the set is of a very high standard. It goes right up to the high trebles and down to the low bass with a most pleasing evenness of range. A very noticeable feature, too, is thet even on the very deepest notes there is not the slightest trace of boominess or cabinet resonance. As a gramo-

phone amplifier it is recommended for use with a low impedance pickup and matching transformer. Another interesting feature which was demonstrated was the remote control, an optional accessory. By means of this it is possible to completely control the set at any distance from it. The control box, measuring only 6 inches by 34 inches, has on it ten buttons, which may be set to any ten stations. By pressing the button marked for the station required, that station is immediately tuned in automatically. In addition, any other station not preselected can be tuned in by using buttons one and ten. Two buttons control the volume. A green pilot light on the control box indicates whether the set is on or off. There is also an additional button, by pressing which the set can be temporarily silenced. When the button is released the set operates immediately. This silencing button impressed us as being most particularly useful. The remote control consists fundamenally of two low voltage motors, one of which drives the volume control and the other the station finder. This is the first remote control we have seen in this country. The set employs two stages of secreengrid radio frequency, screen-grid detector, and an a.f. stage of 227 followed by two 245’s in push-pull. In front of the first valve is a double preselector circuit. The over-all sensitivity of the set is better than 5 microvolts per metre antenna height. Its high degree of sensitivity and selectivity demands that it should be carefully tuned.