N.iniO SICX.II.IXCr SVS IliM 535 



vacuum tubes are connected in parallel and are ojjerated on alter- 

 nating current. In order to take care of the filament warning lamps 

 a resistance is provided in series with each tube filament so that 

 when this filament burns out the voltage will rise sufficiently to light 

 the corresponding lamp. To supply the necessary direct current for 

 the plate potential of the \acuum tul)es and for the operation of the 

 relays, this receixer is provided with a power rectifier tube. The 

 rectifier tube circuit is connected to the high volt;age secondary wind- 

 ing of a power transformer and in connection with a filter system 

 supplies to the recei\'er 110 volts direct current. As an indication of 

 a burnt out rectifier tube filament there is provided a relay connected 

 in series with the rectified current and a green signal lamp connected 

 across the line in series with the contacts of this relay. The lamp 

 will light when the power is turned on only if the rectifier tube is 

 functioning properly. Thus it serves two useful purposes. 



Both the DC and AC types of radio receivers are designed for 

 operation from an open antenna, a double tuned, inductively coupled 

 circuit being employed. The antenna circuit is tuned by means of 

 taps on the loading coil and a small series inductance whose coupling 

 to the loading coil is variable. An adjustable coupling coil is also 

 included in the antenna circuit and serves as a sensitivity control. 

 The secondary circuit to which this coil is coupled is tuned by means 

 of a variable air condenser. All of these controls are on a panel 

 inside the receiver and are inaccessible when the receiver cabinet is 

 locked, thus insuring their remaining in adjustment. 



Four "peanut" vacuum tubes are employed in the radio receiver. 

 The first tube serves as a radio frequency amplifier. By means of a 

 fixed radio frequency transformer sharply tuned to the frequency 

 of the transmitting station, this tube is coupled to the second tube, 

 which acts as a grid leak detector. This arrangement provides addi- 

 tional selectivity and more amplification than if a broadly tuned 

 transformer were used, and is permissible since, in any given system, 

 it is anticipated that the transmitter frequency will remain constant. 

 To adapt the receiver to operate at any other transmitting frequency 

 the transformers may be readily replaced by others of the proper 

 characteristics. The third tube serves as an audio-frequency ampli- 

 fier, being coupled to the detector tube by means of an audio-fre- 

 quency transformer having a frequency characteristic suitable for the 

 transmission of speech or music. The fourth tube serves as a rectifier 

 and is coupled to the amplifier by means of a transformer, sharply 

 tuned to the signaling frequency of 3,000 cycles. This frequency, 

 as noted above, is sufficiently above the preponderant frequencies 



