Palec palec original valve data book0001 free download

File name palec_original_valve_data_book0001.pdf

METHOD OF VALVE TESTING. J1ust what constitutes the best method of testing a valve to determine its general condition, has been the subject of much discussion among radio engineers. Opinions at one time were divided between the relative efficiency of the four existing methods viz: the true mutual conductance, the power output, the grid shift and the emission test. An avalanche of new valves settled the controversy 1>ybringing the emission tester into general favour as a commercial valve tester because it was the only system which could be adapted to incorporate all the following points: l---.Ability to cope with the hundreds of existing valves as well as future releases. 2--Simplicity and quickness of operation. S-Reasonably low selling prices. 4--.Pract.ic~1 accuracy. The true mutual conductance tester. whilst the most accurate, IS purely a laboratory instrument requiring as many controls and meters as there are elements in a valve. Therefore it can be regarded as im- practicable for commercal purposes. The Imitation of the so-called "grid shift," and power output systems, combined with the fact that a well designed emission tester may ~e the more accurate, has brought the latter into universal use. It will be realised that the only thing likely to happen to a radio valve in service, (apart from leakage between elements) is a depreciation of the emitting qualities of the ell-thode element. So why not test a tube for ita emissioD current? , - ~ .~ This' has been confirmed by our own and overseas laboratory eom- When the emission type valve test was first developed, the mistake was made of applying a high voltage to the valve through a voltage dropping resistor. Consequently, the voltage applied to the valve (tested as a diode) depended on the current drain. This. meant that a poor valve - which had a low emission, was tested at a higher potential than a. good one and that true differences of merit could not be arrived at. Then a&ain, there arose the danger of harming a poorish valve through excessive vol~ . age being applied to the grid and injuring the cathode coating. In the "Palec" valve tester, a constant low voltage is applied and th. current drain limited to well below satura tion point. This low voltage is not sufficent to ionise gas if present in a valve _ . , and produce