11-10-2014, 11:33 AM
(11-09-2014, 08:06 PM)Mondial Wrote: Yes, the voltages on the print are all messed up. The highest voltage should be on the plate pin 5, then control electrodes pin 4 and 3 are lower and finally the cathode pin 8 should be the lowest. Your measured voltages seem about right, although the control voltages on pins 4 and 3 are a bit high if you are measuring them with no station being received.
The control voltage is developed across the screen grid resistor of the 6K7 IF tube. As a station is tuned in, the AVC voltage on the 6K7 control grid goes more negative, causing the screen current to be reduced. As the current falls the voltage at the screen rises, and since this voltage is connected to the 6AF6 control electrode, the eye closes.
Check the screen voltage on the 6K7 as you tune in a strong signal. If there is little or no variation in voltage, then that's why the eye is not operating properly.
Here are the numbers on the 6K7
P 3 253v
G2 4 129v
G3 5 3.7v
K 8 3.7v
did find an unsolderd connection in the eye tube plug pin5 re soldered but it made no difference
I get no variation in the eye or voltages when tuning from strong to no station in BC
On SW I do get some voltage and eye movement from 129v to about 160v
R21,25 says should be .47meg I take this to be 470K am I correct?