GROUND RADIO BULLETIN NO. 22 - JANUARY 26, 1950 COMMS DEPT. L.A.D.
AAM RECEIVER MODIFICATION
Several years ago we had a modification to the AAM receiver which consisted of connecting a tinned copper wire from the chassis to the RF selector switch assembly mounting screws. This was done by the manufacturer on all units having serial numbers 170 and above. All receivers already in use at the time of the modification were to be modified at the station, and Dwg. Z-1144. was added to the instruction book to show the modification details. This is referred to as modification "A".
Upon the recommendation of the manufacturer we are now adding modification "B". This consists of replacing the 2.5 Megohm resistor, item 17, with a 5 Megohm, 1 watt resistor (PAA #8191-8291). The time required for the AAM to operate on a failure of the aerophare transmitter will be increased from the present range of 5.5/7.5 seconds to 5.5/12 seconds. After the modification is made the selection of a tube to give the required time delay will not be as critical as previously, and a greater change in time delay tube emission will be permissible before the AAM will fail to provide proper delay action.
This modification should be done to all receivers in the field after ordering and receipt of the new 5 Megohm resistor. After the modifications have been made, the letters "A" and "B” should be stamped or marked with a sharp tool on the nameplate in the space provided for listing modifications*.
CAUTION
Many condensers, both paper and mica, from inventory have been found to be defective in that they have a high resistance reading between terminals. All by-pass condensers should approach 100 Megohms or higher. Filter condensers, especially electrolytic, will be much lower and will vary with capacitance. It is therefore suggested that all replacement condensers be checked before they are put in service.
FORM 9211—2107
