GROUND RADIO BULLETIN NO. 33 - JUNE 21, 1951 COMMS. DEPT. L.A.D.
51N2 RECEIVE
Tubes are continuing to be hard to obtain, and the shortages are expected to increase.
In order to reduce tube consumption as much as possible, it is desired that all type 2C51 (5670) tubes not required in the 51N2 receivers be removed and placed in the spare parts kit for use in receivers that do require them. Specifically, this refers to receivers used on Radiophone circuits, as well as any non-cw reception requirements. The 2C51 item VIII, is the BFO oscillator tube, and is required for cw operation only# Its removal will make a tube available for a cw receiver. The cost of this tube is approximately five dollars each.
PART SUBSTITUTIONS - NC-2-40 RECEIVER
The NC-2-4O 10 mf condensers with mounting brackets (items C52 & C53) pt, no. 9007-6486 are no longer available from the vendor. A Cornell - Dublier 10 mf condenser with wire leads, pt. no. 9007-6476 had been designated as a substitute.
When replacing item C52, the substitute condenser is located in approximately the same location, using the wire leads as supports; however, when replacing item C53, "the condenser is relocated underneath the chassis near the 6J5 tube socket. Care should be exercised in locating these condensers firmly at the bottom of the chassis so they do not interfere with the free movement of the coil rack.
Due to the number of failures of the AVC voltage divider (item R-35), it is recommended that this resistor be replaced with one of a higher wattage rating, The replacement is a v/ire wound, 5 watt, 1500 resistor, PAA pt. no. 9050-3721.
MERCURY RELAYS - 12ACX/12GLX TRANSMITTERS
There have been a few instances where trouble has been experienced with the mercury re-, lays used in the 12GLX2/12ACX2 transmitter power circuits. Tests made in the Ground Radio Shop with a supposedly defective relay failed to disclose any defect. The trouble was finally resolved as being caused by low solenoid voltage supplied to the relay coil. Changes on the transformer tap in the transmitter from II4. to 16 volts allowed proper relay operation.
These relays are designed for operation at 15 volts as stamped on the name plate. Where difficulty is encountered with any of these relays closing properly, the solenoid voltage should be checked and increased if necessary, before ordering replacements.
Generally speaking, trouble from these relays has been extremely rare.
FORM 9211—2107
