05-04-2013, 09:23 AM
GOOD NEWS, everybody!
I got in the rectifier and ballast for this beastie. Using a basic schematic I reconnected everything as it should be, and got started troubleshooting.
First off, I knew that there were issues with the antenna coil, since the primary had pretty much fallen to pieces. I used a generic coil from AES to do the testing.
First up, brought it up slowly on the variac. Everything was looking good, till the rectifier shorted and took itself out. Investigation brought no issues that would have done this externally, so I figure it must have been the tube itself had some sort of internal injury (one side of the tube plates got red hot, but the other, which was in parallel with it, did not). Fortunately, I had bought several spares for stock. Replacing the tube brought all voltages up nicely, with no problems noted.
There was no audio. I found that a Micamold resistor in the cathode circuit of the 43 output tube (also is the screen supply for the 6J7) was open. It appears from the schematic I have that the resistor's value should be around 500-600 ohms. I paralleled two 1K 2W resistors and placed them in circuit, and the audio came to life. There were still RF issues.
I could get RF through the 6J7 (2nd RF/Det) if I touched the grid cap. This was intermittent, cleaning the tube socket cured that. No RF could be forced through the 6K7 (1st RF). I subbed in a new tube, and suddenly there was music coming from the radio! At first, it was pretty much just one station, my inhouse transmitter, across most of the band. Not too unusual for a two stage TRF. I did a quick alignment, including the "rocking" to get the low end to track, and now it gets stations up and down the band, and actually does a darn good job of it!
Tomorrow, I'll clean up my temporary connections, put in permanent replacement 'lytics, and try to fashion a new dial cord pulley for the tuner shaft (the one it had was missing when I got it, and as a result, the dial did not track properly). I figure I can chuck up a shaft extender and use a rat tail file as a lathe. Isn't trial and error fun?
I got in the rectifier and ballast for this beastie. Using a basic schematic I reconnected everything as it should be, and got started troubleshooting.
First off, I knew that there were issues with the antenna coil, since the primary had pretty much fallen to pieces. I used a generic coil from AES to do the testing.
First up, brought it up slowly on the variac. Everything was looking good, till the rectifier shorted and took itself out. Investigation brought no issues that would have done this externally, so I figure it must have been the tube itself had some sort of internal injury (one side of the tube plates got red hot, but the other, which was in parallel with it, did not). Fortunately, I had bought several spares for stock. Replacing the tube brought all voltages up nicely, with no problems noted.
There was no audio. I found that a Micamold resistor in the cathode circuit of the 43 output tube (also is the screen supply for the 6J7) was open. It appears from the schematic I have that the resistor's value should be around 500-600 ohms. I paralleled two 1K 2W resistors and placed them in circuit, and the audio came to life. There were still RF issues.
I could get RF through the 6J7 (2nd RF/Det) if I touched the grid cap. This was intermittent, cleaning the tube socket cured that. No RF could be forced through the 6K7 (1st RF). I subbed in a new tube, and suddenly there was music coming from the radio! At first, it was pretty much just one station, my inhouse transmitter, across most of the band. Not too unusual for a two stage TRF. I did a quick alignment, including the "rocking" to get the low end to track, and now it gets stations up and down the band, and actually does a darn good job of it!
Tomorrow, I'll clean up my temporary connections, put in permanent replacement 'lytics, and try to fashion a new dial cord pulley for the tuner shaft (the one it had was missing when I got it, and as a result, the dial did not track properly). I figure I can chuck up a shaft extender and use a rat tail file as a lathe. Isn't trial and error fun?
