GROUND RADIO bulletin no. 14 - September 29, 1949 COMMS. DEPT. L.A.D.
REPLACEMENT PARTS
The makers of Solar condensers have gone out of business. As a resuit, many substitute items may have to be supplied for condensers ordered from stores. This will also affect condensers in the Spare Parts Kits until new standard items can be selected.
4WTFA MODULATION
A 4WTFA recently overhauled in the shop had normal meter readings. Under modulation the modulator space current meter kicked-up as usual but the percentage of modulation, as measured with a G-232 modulation meter, was only 20 percent* Shorted turns were found in the screen winding of the modulation transformer. The resistance between terminals of the modulation transformer should be as follows:
1-2 = 3.6 ohms 7-9 = 150 ohms
3-4 = 27 ohms All other combinations = 0
5-6 = 14.5 ohms
7-8 = 75 ohms
8-9 = 75 ohms
NC-240 RECEIVER
In some NC-240 receivers modified for crystal control there has been a condition of regeneration in the IF stages. This is usually noted as a very high pitched oscillation or near oscillation. It is caused by the long Bt lead serving the BFO tube through the BFO switch. This condition may be corrected by the addition of a .01 MFB-600 WV condenser (Part No. 8175-3741) between the Bt end of R17 (250,000 ohm BFO plate resistors) and ground.
FORM
9211—2107
