8
1-4-1, VOLTAGE VARIFICATION TESTS
We are now going to measure the B+ 250vdc, the regulated 150vdc, the High Voltage 575vdc and measure and
preset the bias voltage. This will be a no-load condition and the voltages will read 5 to 10% high.
Insure all the cable connections are correct. Turn the OPERATION SWITCH to MOX. There should be no
indication of plate current on the meter monitoring the power supply.
The end of R124 connected to the terminal strip should measure
≈
+250vdc
The end of R124 connected to V11 pin 5 should measure /- 2.0vdc
The metal strip the tube plate parasitic suppressors connect to should measure
≈
+575vdc
Tab 11 of S1 should read a negative voltage. Adjust R206 (BIAS ADJUST) on the rear of the power supply for
the maximum negative voltage it should read
≈
-125vdc
. We will leave it at the max setting for now. If these
voltages are ok power down. Replace the PA cover. Since you are using a known to be good power supply, the
absence of one of these 4 voltages would most likely indicate a wiring fault which needs to be cleared before
you can proceed.
1-4-2, INITIAL BIAS ADJUSTMENT
Insure all the controls and switches meet the
turn on preset “safe” conditions
.
Turn the OPERATION switch
to MOX and allow 10 minutes for warm up.
Turn the FUNCTION switch to CW and adjust the BIAS ADJ on the power supply for 1v on the meter
connected to the power supply test jacks. One volt reflects 100ma of idle current. Return the FUNCTION
switch to AM and turn the OPERATION switch to OFF. If this procedure was successful you are ready to
proceed to the oscillator test procedures. If you are unable to set the idle current then the PA final tubes are bad
or the grid, screen or plate voltage is missing. See figure 12 in the factory manual for aid in isolating this fault.
1-5, OSCILLATORS
There are three oscillators in the system, the carrier oscillator, the heterodyne oscillator and the VFO. We will
address the carrier oscillator first.
1-5-1 CARRIER OSCILLATOR TEST AND VERIFICATION
The carrier oscillator is one half of V1
Power up in the “safe” mode. While waiting 10 minutes for warm-up locate the junction of R5 (56 ohm) and R6
(220 ohm). Connect the scope using a 10X probe to the junction of R5 and R6. When the unit has warmed up
move the FUNCTION switch to CW. You should see approximately 3vpp of 1650KHz on the scope. Adjust T1
for max signal. Move the probe from the scope to the frequency counter. Adjust C1 for exactly 1650KHz.
Return to AM mode. Move the probe back to the scope. Connect a microphone and key the mic, you should see
carrier on the scope when the mic is keyed. You should get the same results when you key the mic in USB
mode and LSB mode. Remove the microphone. Set the OPERATION switch to STBY rotate the FUNCTION
switch through all 4 modes, you should have carrier signal on all modes. The same will be true for CAL and
VOX. Return the controls to the “safe” mode. Plug the telegraph key into the key jack on the rear panel. Turn
the OPERATION switch to VOX and set the FUNCTION switch to CW. When you press the key, you should
see carrier on the scope. Rotate the DELAY control CCW press and release the key and note the fast dropout of
the carrier osc. Rotate the DELAY fully clockwise press and release the key note a delay in drop out of approx.
1 second. Return all controls to the “safe” mode.
This completes the carrier oscillator tests. You have now proven the operation of the carrier oscillator and most
of the function and operation switch functions.