GROUND RADIO BULLETIN NO. 5 - JUNE 10, 1949 COMMS. DEPT. L.A.D.
4WTFA MODULATOR TUBES
The old question of “shall we or shall we not“ has finally been settled* In the future, we shall not leave any tubes plugged into the modulator chassis of the 4WFTA when the transmitter is used for CW only* It must be pointed out, however, that these tubes must be periodically inserted to test the transmitter modulation and that the modulator unit shall always be in working condition* The plate leads for the 828 tube caps should be tied against the leads to the modulation transformer* Modulation tests of 4WFTA transmitters used for CW only will be required during visits by the maintenance inspector.
"TEE" PADS
To permit full modulation of our radiophone transmitters, a line amplifier is used at many stations (see GEN-12A-941, sheet 2). The output of this amplifier is adjusted to a standard level of 0 db which is fed to the speech inputs of the modulators* Because all of our modulators, with the exception of the 601A transmitter, were designed to operate at an input level lower than 0 db, the use of “Tee“ pads is required (see GEN-17A-899). “Tee” pads are mandatory with 4WFTA transmitters used with line amplifiers because the modulator speech input transformer will saturate very rapidly when the input to the transformer exceeds a level somewhat less than 0 db* As the saturation level is approached, the modulation quality is distorted, while during saturation the modulation is zero.
For adjustment of the »Tee» pads refer to GEN-17A-900.
