Show how to test old tube make your own tester sometime in the experience of set owners the question occurs do my tubes need replacement or rejuvenation uvena the signs that lead up to the li question are well known distant stations no longer itinger come in with their customary volume plate current he be comes smaller and hw smaller ailer although tile the B and 0 voltages remain unchanged the volume of local stations begins to ebb all of which indicates that the time has conic como for a diagnosis dl to determine bow badly worn obrn the tubes are this can be done by the use of a tube tester winch which Is not difficult to make only four items are necessary fa first a base from tin an old tube second a tube socket bocket third thorda a voltmeter and fourth a few feet of flexible cable to foglu the lends leads the lends leads should be soldered to the terminals inaldo of the lie old tube base and the corresponding terminals 0 of the socket the voltmeter should be connected in series with the plate lead making all lends 4 ads long enough so that the old tube base may he be plugged anto into any socket of the set leaving tw tits voltmeter and socket of the tester sitting bitting conveniently near theoretically a should be used in place of a voltmeter but practically it has been found that westinghouse voltmeter serves the purpose because of its two seales scales one of volts and tile the other of 75 volts ilia 75 volt velt range lias has a resistance of ohms which Is relatively small tom compared pared to tile the plate resistance it I 1 s this range that Is used as a n milliam meter very few lubor take more mord than 10 milliamperes plate current this voltmeter Is large enough for practically all requirements before making tests upon any tubes use the voltmeter to obtain the tila volt voltage and the lie n B and C voltages then insert the lie meter id the tube tester teeter circuit place tile the tube in the socket and plug the old tube bass base into the socket in the radio set sei tile the meter indication Is proportional to the plate current and since 10 trill roll li amperes ts Is considered as full scale deflection it Is eney easy to estimate the correct plate current if for example the scade reading Is then the afie corresponding milliampere reading will be 8 if the plate current Is lower than 40 per cent of that given by tile the tube manufacturers data for the same B volts the tube should be replaced if the tube Is of the thorl thor aled type such as the UX A it can be rejuvenated |