. QST . ound 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 this furn
. QST . ound 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 this furnishes 50 ma. grid currentand 270 volts bias. The final stage will operatesatisfactorily with grid current as low as 35 ma.,so an 829-B should handle the job without ex-ceeding its normal ratings. Design Considerations In laying out a high-powered amplifier thatrequires conventional cross-over neutralization,symmetry and short leads are mandatory. Thetop-view photograph shows how these ends are HK-54. Fig. 1 — Schematic diagram ofCi — 500-AiMf- feed-through , C3, C4, Cs — 1000-/i/if. button — National VHF-IS with two inside stator and rotor plates removed from each — National TMK-35D, all plates removed except two stator and one rotor, spaced evenly in center of each , C9 — , Cii — 20-;jf. 150-volt , Ci3 — 600-volt (Sprague 80P3).Ci4 — IS-M/if. variable, double spaced (Bud LC-1641).Cn — Disk-type neutralizing capacitor (National NC- 800 A).Ri — 3500 ohms, 10 , R3 — 56 ohms, 1 »4 — 4700 ohms, 2 — 270 ohms, 2 — 25 ohms, 2 watts. the 500-watt 2-meter — 1 turn No. 12 plastic-covered housewire. Loop inside — 2 turns ^«-inch copper tubing, J^-inch Turns 3^ inch , L4 — 5^-inch brass tubing, 10 H inches long, spaced 1^ inches, center to — ^6-inch copper tubing bent into a U 3^^ inches long
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectradio, bookyear1915
