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209-A and 200-A output panels match impedance of the amplifier output of 500 Ω or 250 Ω to the 16 Ω 555 receivers using a 7-A autotransformer. When the emergency key is switched to "off" a 500 Ω resistor is shunted across the amplifier output. |
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41 amplifier: for amplifying disc reproducer and 49 type photoelectric cel preamplifiers. It uses three resistance coupled 239-A tubes with a maximum gain of 41.6 db. |
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Input impedance is 200 Ω with an output impedance of 16,000 Ω. The 390 volts B+ is supplied by the 42 amplifier. The 41-A is designed for 12 volt storage battery operation. The 41-B will also work with the KS-5259 motor generator. The 42-A became available early in 1928, the 41-B in 1930. |
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42 amplifier - single stage ac supplied intermediate amplifier: Input impedance-16,000 Ω, output impedance-250 Ω or 500Ω. Push-pull single stage with two 205-D tubes. Filament voltage is 4-5 volts at 3.2 amps. Plate voltage is 390 at 580 mil. Gain is 24.8 db. There is a starting switch on the front panel for warming up the filaments before switching on the B+. This is to prevent thorium from being deposited on the grids of the 205-D tubes. Care should be taken to keep amplifier tubes separate from rectifier tubes for the same reason. The 42-A became available early in 1928. In 1930 a bank of D-92583 capacitors were made available to replace C-1 to C-8. |
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43 single stage power amplifier: Input and output impedance is 500 Ω. Filament 10 vac. Plate 800 vdc at 125 ma. The output capacity for one 43-A is 33 db, with two in parallel it is 36db. The amplifier draws about 300 watts from the 110 volt line with a power factor of .75. Like the 42, the 43 has a filament starting switch on the front panel. The total amplifier plate current with 211-E tubes should be between 105-150 ma. Both tubes should have similar characteristics. To test for matching without a tube tester, insert only one amplifier tube and allow suffient time for it to warm up. Read the plate current from the meter on the front panel. Test all tubes, being careful not to use tubes that have been previously used as rectifiers. Select two tubes whose plate characteristics differ by not much more than 10 ma. For rectifier tubes the requirements for balancing are not critical. Tubes that have been used as rectifiers must not be employed for amplification. A major cause of failure is from a short between the grid and filament of a rectifier tube or a short in one of the filter capacitors. Unless this is noticed at once it will result in burning out the secondary winding of the 307-A transformer. Take care never to remove both rectifier tubes at the same time while the amplifier is on. Availability of the 43-A was also early 1928. The 610 Ω resistor was added to the capacitor bank on 11-1-34. |
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