4. Calibration The first part of this section covers the preliminary circuit adjustments used for setting-up # new unit or after major servicing, and the second part describes the calibration procedure which should be followed to check the instruments operation before a survey. Figure 20 shows the location of the controls. 4.4.1 Preliminary Adjustments 1. B supply - Adjust R-80 to obtain a B plus of 250 volts. 2. Filter circuit adjustments, a. Introduce a 2400 ops signal to the input (pin 6 of J-1). Capacitors C-6 and C~8 are adjusted to produce maximum attenuation to the 24,00 cps signal as measured at the grid of V-1A. (Set the gain control (R-3) above minimum. A convenient way of obtaining a 21,00 cps signal is to connect pins 5 and 6 of J-1 together, and then pressing the lock-on button. | be. Place a 7200 cps signal on the input and adjust R-10 and R-13 until maximum attenuation is reached (measure at the grid of V-2A). ce Introduce a 60 ops signal and adjust R-15 and R-16 to produce maximum attenuation as measured on the grid of V=2A-. 3. Connect the output of a Telepulse Receiving Station to the Teslepulse Central Station input through a 100 to 1 attenuator. k. First Sehmtt trigger (V-3) sensitivity - Adjust the front panel control (R-3) antil pulses of 10 volts amplitude appear - 46 -