03-07-2014, 10:47 PM
OK, I need help, please.
I finished the recap on the radio a couple of days ago. Dim bulb test, passed. Turned radio on...nothing.
I started by checking voltages:
From C44+ to C44- => 372V
From C46+ to C46- => 300V
Field coil measured something like 1K ohms, but I forget the exact number, seemed OK.
I also checked tube voltages against the service information I got from Chuck. Here are the readings I got:
P-K voltages Measured Expected
RF 44 243 235
36 0.9 230 <=== ?
IF 44 242 240
75 233 175 <===?
42 259 235
<Edit> I tried to make a nice table here, but the extra whitespace characters are being suppressed
The 36 tube measured strange, beyond the very low number shown above. If I measure plate to chassis, I got something on the order of 240V. If I measured cathode to chassis, it was something like 9 V. yet when I measure P-K, I get .9V. What is going on here?
I probed around the 36 and low and behold, I found that the small secondary of the oscillator coil that is attached to the cathode is open. Does this explain the strange measurements I described in the previous paragraph?
Several more questions:
Does the open osc coil explain the high P-K voltage seen at the 75 tube? In other words if the oscillator isn't working, could that mean that current isn't being drawn by the IF and the detector circuits, causing the plate of the 75 to be very high. Also, the P-K of the output 42 tube is somewhat high. Could this also be explained by the open osc coil? Just wondering if I have to look for problems in the vicinity of the 75 and the 42 as well.
Does anyone have any tips on how to repair the open coil? I've never done this before. I searched YouTube and couldn't find any videos showing the repair of an open osc coil. Anyone have a link to a helpful video?
I did look very closely at these two osc coil terminals. I can see extremely thin wires wrapped around the terminals, but I swear that they do not look like they were soldered correctly (cold or non-existent solder joints). Should these in fact be soldered? I would expect so. If I try to resolder, what temperature should I set the iron to? I've read that you need to be very careful wih these tiny wires.
Sorry for the barrage of questions, but this is new territory for me. And of course, thanks in advance!
Jon
I finished the recap on the radio a couple of days ago. Dim bulb test, passed. Turned radio on...nothing.
I started by checking voltages:
From C44+ to C44- => 372V
From C46+ to C46- => 300V
Field coil measured something like 1K ohms, but I forget the exact number, seemed OK.
I also checked tube voltages against the service information I got from Chuck. Here are the readings I got:
P-K voltages Measured Expected
RF 44 243 235
36 0.9 230 <=== ?
IF 44 242 240
75 233 175 <===?
42 259 235
<Edit> I tried to make a nice table here, but the extra whitespace characters are being suppressed
The 36 tube measured strange, beyond the very low number shown above. If I measure plate to chassis, I got something on the order of 240V. If I measured cathode to chassis, it was something like 9 V. yet when I measure P-K, I get .9V. What is going on here?
I probed around the 36 and low and behold, I found that the small secondary of the oscillator coil that is attached to the cathode is open. Does this explain the strange measurements I described in the previous paragraph?
Several more questions:
Does the open osc coil explain the high P-K voltage seen at the 75 tube? In other words if the oscillator isn't working, could that mean that current isn't being drawn by the IF and the detector circuits, causing the plate of the 75 to be very high. Also, the P-K of the output 42 tube is somewhat high. Could this also be explained by the open osc coil? Just wondering if I have to look for problems in the vicinity of the 75 and the 42 as well.
Does anyone have any tips on how to repair the open coil? I've never done this before. I searched YouTube and couldn't find any videos showing the repair of an open osc coil. Anyone have a link to a helpful video?
I did look very closely at these two osc coil terminals. I can see extremely thin wires wrapped around the terminals, but I swear that they do not look like they were soldered correctly (cold or non-existent solder joints). Should these in fact be soldered? I would expect so. If I try to resolder, what temperature should I set the iron to? I've read that you need to be very careful wih these tiny wires.
Sorry for the barrage of questions, but this is new territory for me. And of course, thanks in advance!
Jon
