I.F. frequency is 470 K.C.

BAND - SWITCH SHOWN AT 1st POSITION.
BAND 1

BAND - SWITCH SHOWN AT 2ND POSITION
BAND 2

BAND - SWITCH SHOWN AT 3RD POSITION
BAND 3

TUBE VOLTAGE CHART

Source Voltage 7.0
All voltages as indicated on RCA voltohmyst

GENERAL DESCRIPTION PURPOSE: KARADIO model so is a 3 - Band mobile communications radio receiver for installation in cars, trucks, buses and other vehicles for reception of radio telephone signals.

RECEIVER CIRCUIT:
KARADIO MODEL so is a superheterodyne receiver designed to operate from the 6 - volt battery supply of any vehicle. The circuit employ ed in ALL ranges consists of one stage of tuned R.F., mixer and H.F. oscillator, one stage of I.F., second detector, one stage of resistance coupled A.F. and Beam Power output. Automatic volume control is also provided on all ranges. The 6" permanent magnet dynamic speaker is specially designed for communications use and is equipped with a transformer to correctly load the beam power output stage at: 5500 ohms.

SENSITIVITY: Sensitivity is such that S microvolts or less input signal at antenna plug will produce 5 watt audio output with a signal to noise ratio of 4: 1 or higher POWER OUTPUT: At least 2 watts of audio power is available with 10 % or less distortion. FREQUENCY RESPONSE: While the KARADIO MODEL so is designed to emphasize the voice frequencies for communications work it is also pleasing to the ear on music.

TUBE REQUIREMENTS: KARADIO MODEL so is supplied complete with set of matched tubes which are tested in the receiver at the time of alignment. The tubes ore:

POWER REQUIREMENTS: KARADIO MODEL so is designed to operate on a D.C. voltage source of 5 to
7.3 volts. It is standard practice of most car manufacturers to set the voltage control of cars and trucks at about
7.2 volts. All operating data on KARADIOS are taken with a source voltage of 7 at which voltage the current is 6 amperes. By the use of a non-sya chronous vibrator and 6X5GT rectifier tube, no polarity consideration need be given in the installation of your KARADIO.
INSTALLATION INSTRUCTIONS MOUNTING: The radio unit may be mounted to and directly below the instrument panel at any convenient location. Two holes must be drilled in the stiffening lip of the instrument panel about 1/4" back from the front of the instrument panel. These holes must be large enough to pass the: two No. 8 mounting screws protruding from the top of the radio unit. After the holes are drilled, insert mounting screws of radio in holes, place lock washers and nuts on screws. These nuts must be fastened real tight. It is also very important that the paint be removed from instrument panel lip directly under nuts so that a good ground connection is made Drill a hole to pass a No. 10 machine screw in the fire wall or other convenient place and bolt strap with series of holes to this support and fasten other end to protruding machine screw on back of radio. This is the back support for radio unit and good ground connections must also be considered in this assembly.

The speaker power supply unit is mounted at any convenient location on the fire wall. This is accomplished by drilling a 5 / 15 - inch hole at desired location in fire wall and mounted with threaded stud nuts and washers provided. Care is to be taken that this mounting bolt also forms a perfect ground. This can be assured by scraping the paint from the spot under the mounting nut and washer on the reverse side of the bulk head.

CONNECTIONS: Insert the four-prong plug in lead from speaker into the socket on back side of radio. Connect fused power lead from radio to the ammeter or circuit breaker of the vehicle. A 10 - ampere FUSE is provided in this cable. Never replace this fuse with one of any other size.

ANTENNA: The antenna of the cowl type is recommended and should be 96 to 108 inches maximum length. The model so KARADIO is designed for an antenna of this length and a low capacity shielded lead-in of 30 inches. IT IS IMPORTANT THAT THE ANTENNA LEAD NOT BE CHANGED AS THIS LENGTH IS CORRECT TO MATCH THE ANTENNA INPUT CIRCUIT.

INSTRUCTIONS FOR ELIMINATING MOTOR IGNITION INTERFERENCE: Cut the high tension lead that runs from the center terminal of the distributor to the coil, as close as possible to the distributor end. Screw the distributor suppressor into the lead and reconnect to the distributor, Mount the generator condenser on the generator frame under the ground lead screw. Connect the spade tip on the condenser wire under the battery terminal of the generator. Do not connect it to the field terminal of generator, When checking the car for motor interference, clap the hood down tight with the hood clamps. In some installations it may be necessary to bond the muffler or the transmission housing to the frame of the car. If necessary, bond the motor block securely to the front and rear supports. For bonding. use 1 / 2 - inch copper braid. Further interference may be eliminated by bonding all metal control cables or pipes feeding from the motor side of the firewall into the car. These bonds should be made from the pipes or control cables and soldered to the firewall immediately adjacent to the motor side. In case of tire static, collector springs should be inserted under the hub caps of the front wheels. In some cases it may be necessary to install such collectors in the rear wheels as well. Interference from electric gas gauges may be cured by inserting a " dome light filter " in series with the lead near as possible to the gas tank. In some instances it is beneficial to attach a by-pass condenser from one side of the ammeter to the grounded part of the instrument panel. If the dome light is feeding interference to the antenna, the lead should be cut where it comes from the post under the dash and a switch be inserted in the instrument panel to turn the dome light off and on. A by-pass condenser connected to the dome light lead and grounded at the post would serve in lieu of a switch,

ALIGNMENT:
The I.F. frequency is 470 K.C.; alignment of each band should be made as follows:
First, oscillator trimmers should be adjusted for correct dial calibration at the high frequency end of each band. Then, oscillator padder condensers should be aligned near the low frequency end of each band after adjustment of the oscillator trimmers. Next, antenna and RF trimmers of all bands should be aligned near the high frequency end of each band.
This alignment should be made at a point approximately 15 % or 2 turn of the knob down from the high frequency end of each band. In aligning a receiver, especially the antenna trimmers, it is extremely important that the correct load, which is equal to the antenna, be used. Shielded leads from signal generators or oscillators have a definite capacity and should be considered when testing or aligning is done.
It is preferable to use an indirect connection or a condenser of approxi, mately 100 MMF in series with the signal generator lead and the antenna lead. The reason that this procedure is important is that on all three bands, the primaries of the antenna coils are of high impedance and are designed for the best impedance match at the low frequency end of each band. By using a greater capacity, a loss in accuracy would result.
Individual tubes of the same type will vary slightly in their character. istics and it is well to remember this fact when replacements become necessary. Even though the circuit is designed so as to reduce the effect of such variations to a minimum. The high frequency oscillator first detector tubes should be selected with some care. The tolerance of the inter-electrode capacities is enough in case of some tubes to slightly alter the tuning. This change would be, however, most notice able at the high frequency end of each band.

TABULATION OF PROBABLE TROUBLES, CAUSES. AND CORRECTIVE MEASURES:

Even though all component parts of the receiver have an ample factor of safety, failure may occur in certain individual cases. Of these failures, the most common will probably be due to some defect in one of the tubes. To find this defect, check tubes on a reliable tube check er, or by substituting spare tubes. If the failure is a short in either the plate or screen circuits, the filter resistors and condensers associated with the circuit in question should be checked with a reliable volt-ohmeter. To check these circuits it is preferable to use the point to point system, in which the chassis is always negative, except the hot side of the filament circuit, which will be negative if the positive automobile battery terminal is grounded to the frame of the car. Then by applying the positive lead of the volt-ohmeter directly to the tube socket contacts and the negative lead to the chassis, it will show which of the component circuits are at fault, by a total absence of voltage or a large difference from the correct voltage from those given in the chart of voltages. If a by-pass condenser is found to be at fault re place with new condenser. Also, check the resistors associated with the faulty condenser. If they have been found to have been hot due to the shorted condenser, it is best to replace it also to forestall future trouble.

Other possible failures, such as open circuits caused by poor connections can be likewise located by the above point to point system in accordance with the chart of voltages. Open by-poiss condensers are apt to cause either a loss of sensitivity or oscillation in some portion of the circuit. In such cases the fault can be easily located by temporarily connecting a condenser of known quality in parallel with each unit that is under suspicion.

Intermittent or noisy reception is almost always caused by a poor connection, a by-pass condenser intermittently opening up, or a bad tube, Such faults are often rather difficult to find, but usually can be located by lightly tapping each circuit element or component part with a light rubber hammer or insulated rod.

In case of failure, it is advisable to check the vibrator, the fuse and the "A" lead connections as the first probable causes. If the set blows fuses repeatedly, the most likely cause will be sticking vibrator; in which case the vibrator should be replaced. If the set upon test shows to be drawing excessive current immediately upon turning the set on with a good vibrator and 6XSGT in place, the most likely trouble will be shorted buffer condenser, part No. C-16. If the droin gradually builds up, the trouble most likely will be one of the filter condensers, or one of the by-pass condensers.