177. Troubles on PG-1 Equipments. -Very little trouble should be experienced with this apparatus. In case serious trouble develops while the equipment is in operation, switch over to the other amplifier. To do this start the motor-generator set of the amplifier not in use. Turn the snap switch below the storage battery ammeter to the "ON" position. Close the lever switches on the input panel of the amplifier rack to be used. Switch the loudspeakers from the rack in use to the one to be used. Open the lever switches of the input panel of the rack giving trouble, and stop its motor-generator set.

The following are some of the troubles which may develop:-

(a) A hum may develop due to a dirty commutator on the 1000 volt or 15 volt generator. Occasionally the 250 volt machine may also give this trouble. This trouble can be avoided by keeping the commutators clean at all times. For instructions in cleaning commutators see section 36.

(b) If the plate current milliammeter reading suddenly increases to a great extent when the equipment is in operation, it is a sign that one of the UV-845 tubes has become defective. When this condition is noticed the tubes should be inspected for abnormal appearances. The usual indication is that the plate of one tube has become almost white hot. If a tube burns out it can be readily detected by its failure to light. In this case it will be noticed that the reading of one of the plate current milliammeters will have decreased a little.

(c) If for any reason, one of the tubes in the voltage amplifier becomes excessively "microphonic" a ringing sound will be noticed in the monitor speaker whenever the amplifier panel is gently tapped. This condition should be remedied by immediately replacing the defective tube with a new one.

(d) If sound is heard from both projectors at the same time, it is usually an indication that dirt has collected on the relay fader contact points. The contact points may be readily cleaned by passing a piece of rough paper between the contacts. Do not use sand paper or other abrasive. The location of this relay is shown in Figure 116.

(e) If the plate current of the UV-845 tubes drop to zero while the filaments remain lighted, it is an indication that the circuit of the 1000 volt generator is open. Check the 1000 volt fuses at the back of the panel (see Figure 116). If this fuse is O.K., test the 1000 volt fuses in the fuse box at the M-G set. Two 1000 volt fuses are used in parallel in this box. They are the two long fuses in the box containing three fuses. (Use 2300 volt, 1.3 ampere fuses for replacement.)

If the plate current of the UX-210 tubes drops to zero while the filaments remain lighted check the fuse in the 500 volt line at the back of the panel (see Figure 116) and the 500 volt fuse in the M-G set fuse box. This fuse is mounted in the same box with the two 1000 volt fuses. (Use 600 volt, 1.8 ampere fuses for replacement.)

9