Tips and [?]ottings.

Radio Record, Volume II, Issue 13, 12 October 1928, Page 27

Tips and [?]ottings.

a eel A Fine Power-Valve. AFTER a lengthy trial of the Philips C603 super power-valve in the last three stages of double-impedance, it is quite evident that this is a valve that will give great volume in the last stage, and give high quality at the same time. "Megohm" has run this valve for several weeks with raw A.C. on the filament, and on that account grid-bias is accordingly slightly increased over the stipulated figure. The excellence of this valve is to a great extent on account of the heavy plate current of 18 to 20 mils passed at voltages approaching 150, the maximum normal grid bias being 27 volts. This

™~™ six-volter is just what many listeners require in the last stage. "Floating" A Battery Hum. AN experimenter, testing out the idea of floating dry-cells across an A charger to supply filament current, says :-At first it was found that there was a decided A.C. hum, which became worse as the cells were older. This was corrected by the use of a simple choke, made with 25 feet of wire from the secondary of a Ford coil, wound on an iron core (a common wire nail) and shunted by rheostat. Experiment may be necessary to suit this to a set; beginning with ten feet of wire and gradually increasing the amount. The wire mentioned is 42’s. The Double-Roll Speaker. A WELLINGTON constructor says this speaker is all that is claimed for it. Good quality wall-paper with a floral pattern was used for the diaphragm. ss