01-20-2011, 07:35 PM
Hi
New member here. I am not exactly a newbie but I don't have a lot of experience. I have done about 20 radios in the past 10 years.
My 37-630 is driving me nuts. Most of the time it doesn't work but sometimes it works great. The problem appears to be bad filter caps but I have checked them on a Heathkit condensor checker and they check good, both value and leakage. Most of the time the radio makes what sound like the 120HZ growl which would indicate bad filter caps but occasionally the problem totally goes away. It went away long enough for me to give the set a good alignment and it worked like a champ on all three bands. I was ready to put it back in the cabinet but checked it one last time and the problem was back. When the problem is present I measure 15 to 17 VAC on C62, 7 to 8 VAC on C60 and 3.5 VAC on C18. I would think these voltages should be a few tenths at most. Also the problem is not nearly as apparent on the high shortwave band. Last night when the BC was totally unuseable I got WWV clearly at 15 MHz with just five feet of antenna wire. The loudness of the growl is controlled by the volume control and it does vary somewhat over the band. I have reflowed the solder on the filter caps, twice. The value of the field coil is not specified on my schematic but I measure about 1150 ohms which I am guessing is about right. The noise goes away completely when I pull the grid cap off the 6Q7. Same thing on the 6A8 but I don't know whether that means the problem is in the input or the output of the 6A8. When the problem is present I can usually get a very faint station on the broadcast band which is at the right freq which makes me think the oscillaator is ok.
I have changed out all the caps I could get to without tearing into the RF sub-chassis which I really don't want to do. The resistors I can get to check out ok also
I have test equipment. O'scope, frequency counter, Heathkit signal generator, digital and analog cap checker and several multimeters both digital and analog.
Your thoughts and guidance will be greatly appreciated.
Jim
PS I just realized I have not measure the B+ ripple when the problem was not present. I guess I'll go do that now.
New member here. I am not exactly a newbie but I don't have a lot of experience. I have done about 20 radios in the past 10 years.
My 37-630 is driving me nuts. Most of the time it doesn't work but sometimes it works great. The problem appears to be bad filter caps but I have checked them on a Heathkit condensor checker and they check good, both value and leakage. Most of the time the radio makes what sound like the 120HZ growl which would indicate bad filter caps but occasionally the problem totally goes away. It went away long enough for me to give the set a good alignment and it worked like a champ on all three bands. I was ready to put it back in the cabinet but checked it one last time and the problem was back. When the problem is present I measure 15 to 17 VAC on C62, 7 to 8 VAC on C60 and 3.5 VAC on C18. I would think these voltages should be a few tenths at most. Also the problem is not nearly as apparent on the high shortwave band. Last night when the BC was totally unuseable I got WWV clearly at 15 MHz with just five feet of antenna wire. The loudness of the growl is controlled by the volume control and it does vary somewhat over the band. I have reflowed the solder on the filter caps, twice. The value of the field coil is not specified on my schematic but I measure about 1150 ohms which I am guessing is about right. The noise goes away completely when I pull the grid cap off the 6Q7. Same thing on the 6A8 but I don't know whether that means the problem is in the input or the output of the 6A8. When the problem is present I can usually get a very faint station on the broadcast band which is at the right freq which makes me think the oscillaator is ok.
I have changed out all the caps I could get to without tearing into the RF sub-chassis which I really don't want to do. The resistors I can get to check out ok also
I have test equipment. O'scope, frequency counter, Heathkit signal generator, digital and analog cap checker and several multimeters both digital and analog.
Your thoughts and guidance will be greatly appreciated.
Jim
PS I just realized I have not measure the B+ ripple when the problem was not present. I guess I'll go do that now.
