Radio Broadcast (May 1927-Apr 1928)

Record Details:

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JANUARY, 1928 PUSH-PULL AMPLIFICATION— WHY? 205 LISTS OF PARTS TL — Samson Power Block, Type 210, Containing Power Transformer and Two Filter Choke Coils .... $ 37 00 Tobe Condenser Block, for Samson Power Amplifier, Containing the Eleven Necessary Condensers . . 38.00 R: — Electrad 7200-Ohm Type C "TruVolt" Resistance, 50 Watts . . . 2.25 R2 — Electrad 420-Ohm Type C "TruV'olt" Resistance, 25 Watts ... 1.50 R3 — Electrad 50,000-Ohm Variable Resistance, Type T-500 . . . '3 .50 R$ — Tobe 10,000-Ohm Veritas Resistance 1. 10 T — Samson Input Push-Pull Trans \ former, Tvpe Y f L2— Samson Output Push-Pull Choke, ( '9-5° Type Z " 12 — Eby Binding Posts .... 1.80 4 — Benjamin Sockets 3.00 2 — RCA ux-210 (Cunningham cx310) Tubes 18.00 1 — RCA ux-874 (Cunningham cx 376) Tube 5.50 1 — RCA ux-281 (Cunningham cx 381) Tube j 7.50 Total $138.65 The circuit diagram has been marked with figures corresponding to the terminal markings on the power block and the condenser block. The arrangement of the apparatus on a single large baseboard makes it a simple matter to construct it and the circuit diagrams and photographs given herewith should supply all the necessary information. All of the transformer cases, and also the case of the condenser block, should be connected to the negative B, as indicated in the schematic diagram, to prevent hum. This grounding can generally be most readily accomplished by running a lead from the negative B to the mounting screws of the various units. The wire can be fastened under these mounting screws. Remember that the voltages de livered by the transformer are very high and therefore care is necessary in making all of the connections. The 50,000-ohm resistance is the only variable control in the entire unit, and it is used to obtain accurate adjustment of the detector voltages. When the construction has been completed, the special plug on the power input side of the Samson transformer may be inserted in the correct manner and connected to the ax. light socket. When this is done, the tubes should light and the regulator tube should glow with a pinkish light. In operation, the transformer block may become somewhat warm, but if it becomes so hot that the hand cannot be comfortably held on it, it indicates some error in the wiring. The input terminals of the device should be connected to the output of the first stage of the receiver and the loud speaker then be connected to the output of the amplifier. If carefully constructed and properly operated, the unit will be found capable of giving excellent reproduction. FIG. 5 This is a complete circuit diagram of the Samson push-pull power amplifier. The various numerals on the units correspond with the markings on the terminal blocks on the various parts; numbers in circles indicate terminals on the condenser block. This amplifier employs two 210 type tubes in the push-pull circuit, a type 281 tube as the rectifier, and an 874 type regulator tube. The connections to the socket holding the latter tube are indicated in the diagram. The P and F minus terminals on the socket are connected in the filter circuit as shown at the point marked "874 B K." on the diagram. The two corresponding contacts on the tube are short-circuited inside of the tube base during the process of manufacture and, therefore, if the regulator tube is removed from its socket while the power is on, the circuit is automatically opened and damage to the filter condensers thus prevented. The G post on the socket connects to the + 90 voltage tap and the F + terminal connects to B minus Condensers Mounted in One Block 5,000u< 10,000w<R4 B BLOCK 1100 (j : TTTTTTI > 1100. 400 V. D C. G( ' -1500 V. D.C. C BLOCK Hi l50 000"f «3 TTTT f5 -200 V. D C. U 45 ( 45 c 310c •30 1 R2 RESISTORS