. QST . y, the appropriate resistors should bechanged accordingly. The transmitter coils should be checked witha grid-dij) meter to be sure they tune to the rightfrequencies — the oscillator coil to Mc, andthe doubler and final coils to 29 Mc. — with theircondensers about one-half capacitance. If thetransmitter is tuned up on Mc, giving output frequencies from may be switched in without any you plan to use widely separated frequenciesit will be necessary to retune all stages whenswitching crj^stals. No trouble was experienced in getting thetransm
. QST . y, the appropriate resistors should bechanged accordingly. The transmitter coils should be checked witha grid-dij) meter to be sure they tune to the rightfrequencies — the oscillator coil to Mc, andthe doubler and final coils to 29 Mc. — with theircondensers about one-half capacitance. If thetransmitter is tuned up on Mc, giving output frequencies from may be switched in without any you plan to use widely separated frequenciesit will be necessary to retune all stages whenswitching crj^stals. No trouble was experienced in getting thetransmitter on the air. However, there was a (Continued on page 112) Cable connections allterminate at the rear ofthe chassis (bottom in thisunderside view). Audiocontrols are equipped withextension shafts so theycan be mounted near theassociated tubes and thusavoid undue hum pick-upon leads. If normal wiringand layout practices areobserved, there are nocritical points other thanthose mentioned in A 500-Watt 144-Mc. Amplifier High Efficiency at Moderate Cost with War-Surplus Triodes BY LEONARD F. GARRETT,* W7JIP THE idea of running high power is attractiveto many 2-meter men, but the cost of thetubes and other components often proves tobe a stumbhng block. The amplifier describedhere doesnt quite make the kilowatt level, but itwill handle 500 watts with ease, and with goodefficiency. It is built around surplus HK-54s thatwere purchased for two dollars each, so the totalcost is far below that for a tetrode amplifier ofsimilar power level using new tubes. Much of the low-drive advantage of tetrodesfades when they are used at frequencies near themaximum at which they are capable of operatingwith reasonable efficiency. A 9903 or an 829-B *3003 71st Ave., Portland, Ore. is customarily used to drive high-powered tetrodeamplifiers on 144 Mc, and this triode amplifierwill get along nicely with the same. The 9903driver here runs at 105 watts input (700 volts at150 ma.) and
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectradio, bookyear1915
