01-22-2018, 03:08 PM
In the course of checking some voltages in the radio chassis, I discovered that the AGC voltage goes to about +12VDC which is not necessarily what I was expecting. The grid bias at the output tubes signal grids are at -19.9VDC. That does not change during warm-up but after about two minutes the audio comes up. I also discovered by measuring the voltages on the cathode resistors of the IF tubes that the 1st IF appears to rise to beyond 8VDC and goes all the way to +131 volts after a while! The 68 ohm cathode resistor measured about 72 ohms and since the voltage there was so high, I decided to replace it with another 68 ohm resistor. That resistor performed the same way and also wound up measuring about 70 ohms or more after cycling one time with the +131volts showing up on the cathode circuit. The tube checks OK on the tube tester and has good emission. I suspect the tube socket is defective and has a B+ internal bridge in it.
So it appears I need to order some Loctal sockets. These will not be easy to change. I am thinking about changing this one to a conventional Octal socket and replacing the 1st IF tube with a suitable Octal base tube. I never saw any real advantage to Loctal tubes and sockets.
Joe
So it appears I need to order some Loctal sockets. These will not be easy to change. I am thinking about changing this one to a conventional Octal socket and replacing the 1st IF tube with a suitable Octal base tube. I never saw any real advantage to Loctal tubes and sockets.
Joe