07-05-2016, 01:24 PM
The rest of the capacitors were restuffed and reinstalled. Any out of tolerance resistors not yet replaced were replaced. All of the original tubes that tested good were replaced, and any bad ones replaced. A new power cord was attached. I assumed that flat brown vinyl (likely originally rubber) is appropriate for 1946. I then carefully examined the chassis for unsoldered joints and solder blobs. I then checked once again for any B+ shorts. The speaker was plugged in, and an antenna wire attached. I pulled the rectifier tube and powered up the chassis using a Variac through a watt meter. I started at zero volts and gradually increased the line voltage while watching the watt meter. All the tubes lit up and current draw was normal.
I then reinstalled the rectifier tube and monitored B+ with my DVM. I again powered up the chassis with my Variac through a watt meter while monitoring the B+. Power was increased at about 10 volt increments, allowing time for the new filter caps to reform. The band switch was set to the broadcast band and the volume control set a maximum. At about 80 volts AC I heard some noise. I increased the AC to 115 volts. The radio actually worked on all bands. The volume control was smooth and free of noise. The tone control, which was an area of concern, seemed to work OK although I’m sure not as well as it should, since the resistance had drifted from 6meg to 16megs! At maximum CCW, bass boost or loudness compensation was reduced. As the control was rotated clockwise to about ½ rotation, bass increased. Further CW rotation reduced the treble. So for most fidelity the control should be centered. CCW rotation reduces the bass, and CW rotation reduces the treble. This seemed to agree with the schematic.
The next step is alignment of the two IF stages and 10 bands of trimmers! At this writing I have completed alignment of the IF stages and Shortwave #3 band. I was concerned about this band since my signal generator only goes up to about 12mHz with any stability. I have to use harmonics for adjusting anything above 12mHz. So to set the SW3 band to scale at 21mHz, I set the generator to 10.5mHz. I use a frequency counter to calibrate the generator. SW3 was easier than I thought it would be. Even the image frequency appeared where it should have been. All that’s left is to complete the alignment, clean the cabinet, and reassemble.
Photos of the completed chassis are attached.
I then reinstalled the rectifier tube and monitored B+ with my DVM. I again powered up the chassis with my Variac through a watt meter while monitoring the B+. Power was increased at about 10 volt increments, allowing time for the new filter caps to reform. The band switch was set to the broadcast band and the volume control set a maximum. At about 80 volts AC I heard some noise. I increased the AC to 115 volts. The radio actually worked on all bands. The volume control was smooth and free of noise. The tone control, which was an area of concern, seemed to work OK although I’m sure not as well as it should, since the resistance had drifted from 6meg to 16megs! At maximum CCW, bass boost or loudness compensation was reduced. As the control was rotated clockwise to about ½ rotation, bass increased. Further CW rotation reduced the treble. So for most fidelity the control should be centered. CCW rotation reduces the bass, and CW rotation reduces the treble. This seemed to agree with the schematic.
The next step is alignment of the two IF stages and 10 bands of trimmers! At this writing I have completed alignment of the IF stages and Shortwave #3 band. I was concerned about this band since my signal generator only goes up to about 12mHz with any stability. I have to use harmonics for adjusting anything above 12mHz. So to set the SW3 band to scale at 21mHz, I set the generator to 10.5mHz. I use a frequency counter to calibrate the generator. SW3 was easier than I thought it would be. Even the image frequency appeared where it should have been. All that’s left is to complete the alignment, clean the cabinet, and reassemble.
Photos of the completed chassis are attached.
