Laboratory Jottings

Radio Record, Volume IV, Issue 14, 17 October 1930, Page 8

Laboratory Jottings

Philips Combination TH degree of sensitivity obtainable with four valves has been ably demonstrated by Philips Radio Combination. In this receiver there are two stages of screen grid, a leaky grid detector and a power pentode with four hundred volts on the plate. This is coupled through a special output transformer to the dynamic speaker, the field ef which is energised by a separate transformer and rectifier, In appearance the Philips is something out of the usual, The two control knobs are mounted on a moulded bakelite case, and the remainder of the set and speaker is hidden away under the cabinet work. The two controls, tuning and volume, make for a decidedly neat appearance, while the two switches, gramo-radio and off-on, complete the panel controls. The drum control cornrises a transparent scale with a lamp and hair-line indicator, and is particularly smooth in operation, making very fine tuning possible. The volume control, fitted on the radio side makes an excellent control until a strong local station has to be tuned in, when it is necessary to remove the aerial and substitute it by a small piece of wire. It is interesting in this connection to note that the set will not operate on the local station without an _ aerial, though when even a foot of wire is used, there is more than ample volume. This illustrates that the shielding is most effective, On removing the grate covering from the back of the set, one is struck by the very complete shielding, for there is absolutely’ nothing to be seen except the power pentode and the rectifier. The shielding is all in heavy iron, and is of the appearance that it will stand considerable knocking before altering its shape. The removal of the cover automatically cuts off the current. Sensitivity-Though somewhat more sensitive on the higher frequencies than on the low, the set gives uniformly good results. It will bring in the main Australian stations under ordinarily good conditions with a reserve of power and will generally give enough strength in relation to noise to make listening worth while. In other words, it is as powerful as is required under ordinary conditions.

Further increases in power raise the noise level and make the extra power of no value. Under test it was capable of bringing in Japanese stations regularly and an occasional American under very favourable conditions. Selectivity-This was such that with a long aerial 2BL could be brought in with only a faint background of 2YA. We have had 2FC and 2BL, but these only late, and rarely. The set is-as selective as required under New Zealand conitions.

Fidelity -The tonal qualities are good. It is bright and clear, and is somewhat different from the ordinary. ‘This is due, no doubt, to the pentode in the last stage, and for this reason it takes some time before one becomes accustomed to the tone. After the usual duller sound one is likely to accuse the Philips of harshness, but time disillusions him. The definition and the ability to separate instruments is more marked than usual. On measuring the cut off, it was noticed that signals fall off at 4500 and disappear at 6000. The bass goes down to below 40, but this lower register is not accented. The high cut off eliminates much of the gramophone scratch. There is a filter in the receiver that gives more prominence to the bass should it be desired, but in our opinion the set is better without it. Operating Cost.-83 watts an hour or that taken by an ordinary bright light. The cost, where electricity is 2d. a unit, is six hours for a penny-surely moderate. The set will handle comfortable volume for a large room without overloading. In summing up, the set is one designed for average use without wasting either space or expense on components that will not be required for average use. Hverything is of the best and doing its job to the fullest.