Radio today (Sept 1935-Dec 1936)

DRY ELECTROLYTICS (From page 38) denser, then the working voltage rating of the condenser does not need to he considered in relation to the surge voltage. The working voltage rating must, of course, exceed the applied working voltage, but from an economical standpoint should not be higher than necessary. "When the measured surge voltage (read as described above) exceeds the highest obtainable surge voltage rating of the condenser, then it is important that the working voltage rating of the condenser be chosen as close as possible to the actual working voltage applied in accordance with the following explanation. "The accompanying chart shows a typical voltage characteristic of a radio filter circuit during the starting cycle (that is, until the tubes warm up). It will be noted that in this particular case the actual surge voltage, without the condenser connected, reaches 550 volts. If a condenser rated at 500 volts DC working (see Fig. 1 on the chart) is connected across the circuit, it will draw very little leakage current and this load will only lower the surge voltage to about 540 volts. Since this value is higher than the sparking voltage of most condensers, sparking will take place and damage of the condenser may result. Importance of leakage current "A 450 volt DC working condenser (see Fig. 2 in chart) or less, depending on the actual working voltage encountered in the radio set, would have a higher leakage current at voltages above its own rating and thus hold the surge voltage down to roughly 490 volts. As this is less than the critical voltage where sparking starts, there should be no trouble experienced. The above explanation is one of principle only and the values given are solely for demonstration of this principle, as cases vary and no direct values would apply in general. However, it will serve to correct the false idea gained by many people that the higher the working voltage of the condenser, the less apt it is to oredk down on momentary voltage surges. "The particular action just described is subject to change with time, as the leakage current will drop slowly over an extended period. Theoretically, therefore, the regulation characteristic will become less pronounced and other factors of design must be relied upon for continued service past this point. "Referring again to the chart, a condenser rated at 400 volts DC working would work continuously without heating at the 375 volts (see Fig. 3 on the chart) shown as the maximum working potential. This working voltage should always be measured at the highest input voltage that might ever be encountered on the radio transformer primary, for obvious reasons. For the particular characteristics shown in the chart, a working voltage of 400 would be the safest to use and it would provide greater leakage current drain than a condenser of higher working voltage when surge voltages above 400 are encountered during the heating cycle. If a rating higher than 400 were used, it would offer proportionately less protection, due to the decreased leakage and higher surge voltage that would result, as explained above. "If radio service engineers will study carefully the points outlined above regarding the proper voltage ratings of condensers, they will be assured of long, trouble-free condenser life, with low initial cost (due to reduced voltage ratings)." (To page 42) "HERE'S A TUBE THAT NEVER LETS YOU DOWN... I'LL TELL YOU WHY!" # "When you'buy a Sylvania tube, you're buying dependability! Here's what I mean. Before those tubes leave the factory they have received 8o separate tests. That's for my protection . . . and yours. Naturally they carry a definite written guarantee . . . again, wVre both protected! "When it comes to price . . . that's dependablejtoo. And the list price is fair. You see, it'pays to do business with that kind of a company ... I always know where I stand!" You can make your tube business as dependable as this man's! You can get complete sales and technical information by writing to the Hygrade Sylvania Corp., Emporium, Pa. SYLVANIA THE SET-TESTED RADIO TUBE 40 Radio Today