Audio distortion is usually caused by a grid bias problem. Measure pin #5 in relation to pin #8 on your 50L6. Pin number 5 must be around 5 volts negative. If zero or positive you will have distortion. A leaky coupling cap, open resistor or bad 50L6 can cause this problem.
12Q7 or 12SQ7 must have near zero volts on grid #1. If distortion is heard on strong stations the coupling cap to grid #1 on this tube may be leaky.
Be sure the speaker cone isn't rubbing. Push lightly in different places on the speaker to see if this makes a difference.
Norm
: I'm working on a 1946 Crosley that has a 12A7 mixer, a 12Q7 detector, a 12SK7 IF amplifier, and a 50L6 audio output tube. The radio was a mess. I have had to replace much of the wiring in addition to the capacitors and many resistors. It had been lifeless until I replaced the audio output transformer. Now it works, but the sound is distorted: almost as if the sound is coming through water. The new audio output transformer I installed has a primary of 2,500 ohms and a secondary of 8 ohms. Voltage on all the tubes seems OK. As I said, all the capacitors, including the filter capacitors have been replaced. There is some hum, but not an extraordinary amount. I'm no longer sure where to look for problems. Any advice would be appreciated. One other question: I'm far from an expert at reading schematics, but it seems as if there are a couple of deviations between the factory wiring of this radio and the schematic. Is that possible, or is it more likely that I'm not reading it correctly? Any help would be appreciated.
: Audio distortion is usually caused by a grid bias problem. Measure pin #5 in relation to pin #8 on your 50L6. Pin number 5 must be around 5 volts negative. If zero or positive you will have distortion. A leaky coupling cap, open resistor or bad 50L6 can cause this problem.
: 12Q7 or 12SQ7 must have near zero volts on grid #1. If distortion is heard on strong stations the coupling cap to grid #1 on this tube may be leaky.
: Be sure the speaker cone isn't rubbing. Push lightly in different places on the speaker to see if this makes a difference.
: Norm
: : I'm working on a 1946 Crosley that has a 12A7 mixer, a 12Q7 detector, a 12SK7 IF amplifier, and a 50L6 audio output tube. The radio was a mess. I have had to replace much of the wiring in addition to the capacitors and many resistors. It had been lifeless until I replaced the audio output transformer. Now it works, but the sound is distorted: almost as if the sound is coming through water. The new audio output transformer I installed has a primary of 2,500 ohms and a secondary of 8 ohms. Voltage on all the tubes seems OK. As I said, all the capacitors, including the filter capacitors have been replaced. There is some hum, but not an extraordinary amount. I'm no longer sure where to look for problems. Any advice would be appreciated. One other question: I'm far from an expert at reading schematics, but it seems as if there are a couple of deviations between the factory wiring of this radio and the schematic. Is that possible, or is it more likely that I'm not reading it correctly? Any help would be appreciated.
: Audio distortion is usually caused by a grid bias problem. Measure pin #5 in relation to pin #8 on your 50L6. Pin number 5 must be around 5 volts negative. If zero or positive you will have distortion. A leaky coupling cap, open resistor or bad 50L6 can cause this problem.
: 12Q7 or 12SQ7 must have near zero volts on grid #1. If distortion is heard on strong stations the coupling cap to grid #1 on this tube may be leaky.
: Be sure the speaker cone isn't rubbing. Push lightly in different places on the speaker to see if this makes a difference.
: Norm
: : I'm working on a 1946 Crosley that has a 12A7 mixer, a 12Q7 detector, a 12SK7 IF amplifier, and a 50L6 audio output tube. The radio was a mess. I have had to replace much of the wiring in addition to the capacitors and many resistors. It had been lifeless until I replaced the audio output transformer. Now it works, but the sound is distorted: almost as if the sound is coming through water. The new audio output transformer I installed has a primary of 2,500 ohms and a secondary of 8 ohms. Voltage on all the tubes seems OK. As I said, all the capacitors, including the filter capacitors have been replaced. There is some hum, but not an extraordinary amount. I'm no longer sure where to look for problems. Any advice would be appreciated. One other question: I'm far from an expert at reading schematics, but it seems as if there are a couple of deviations between the factory wiring of this radio and the schematic. Is that possible, or is it more likely that I'm not reading it correctly? Any help would be appreciated.
Looks like you might have -3.4 volts on pin #5 in relation to #8. If that's the case it's ok. A little low but won't cause distortion. .7 volts on 12SQ7 grid is ok. The resistor difference isn't a problem.
Can you try a different speaker or check if the cone rubs? Is the distortion on all stations, strong and weak?
Not excactly sure what is meant when you measure against B- ? You mention 11.8 on pin #5 and 3.4 on pin #8. This makes pin #5 positive and will cause distortion..
Norm
: Hello, Norm. When you say to measure pin #5 in relation to pin #8, I believe you mean to put the tester leads on those pins. When I do that, I get -3.4 on pin 5 and 3.4 on pin 8. Measured against B-, I get 11.8 on pin 5 and 3.4 on pin 8. If I understand you right, that is what I would expect to get. I did notice that the load resistor is 420,000 ohms and the schematic says it should be 470,000. Does the voltage on the 50L6 sound correct? Pin 1 on the 12SQ7 has .7 volts. What do you think?
: : Audio distortion is usually caused by a grid bias problem. Measure pin #5 in relation to pin #8 on your 50L6. Pin number 5 must be around 5 volts negative. If zero or positive you will have distortion. A leaky coupling cap, open resistor or bad 50L6 can cause this problem.
: : 12Q7 or 12SQ7 must have near zero volts on grid #1. If distortion is heard on strong stations the coupling cap to grid #1 on this tube may be leaky.
: : Be sure the speaker cone isn't rubbing. Push lightly in different places on the speaker to see if this makes a difference.
: : Norm
: : : I'm working on a 1946 Crosley that has a 12A7 mixer, a 12Q7 detector, a 12SK7 IF amplifier, and a 50L6 audio output tube. The radio was a mess. I have had to replace much of the wiring in addition to the capacitors and many resistors. It had been lifeless until I replaced the audio output transformer. Now it works, but the sound is distorted: almost as if the sound is coming through water. The new audio output transformer I installed has a primary of 2,500 ohms and a secondary of 8 ohms. Voltage on all the tubes seems OK. As I said, all the capacitors, including the filter capacitors have been replaced. There is some hum, but not an extraordinary amount. I'm no longer sure where to look for problems. Any advice would be appreciated. One other question: I'm far from an expert at reading schematics, but it seems as if there are a couple of deviations between the factory wiring of this radio and the schematic. Is that possible, or is it more likely that I'm not reading it correctly? Any help would be appreciated.
: Hi Mike
: Looks like you might have -3.4 volts on pin #5 in relation to #8. If that's the case it's ok. A little low but won't cause distortion. .7 volts on 12SQ7 grid is ok. The resistor difference isn't a problem.
: Can you try a different speaker or check if the cone rubs? Is the distortion on all stations, strong and weak?
: Not excactly sure what is meant when you measure against B- ? You mention 11.8 on pin #5 and 3.4 on pin #8. This makes pin #5 positive and will cause distortion..
: Norm
: : Hello, Norm. When you say to measure pin #5 in relation to pin #8, I believe you mean to put the tester leads on those pins. When I do that, I get -3.4 on pin 5 and 3.4 on pin 8. Measured against B-, I get 11.8 on pin 5 and 3.4 on pin 8. If I understand you right, that is what I would expect to get. I did notice that the load resistor is 420,000 ohms and the schematic says it should be 470,000. Does the voltage on the 50L6 sound correct? Pin 1 on the 12SQ7 has .7 volts. What do you think?
: : : Audio distortion is usually caused by a grid bias problem. Measure pin #5 in relation to pin #8 on your 50L6. Pin number 5 must be around 5 volts negative. If zero or positive you will have distortion. A leaky coupling cap, open resistor or bad 50L6 can cause this problem.
: : : 12Q7 or 12SQ7 must have near zero volts on grid #1. If distortion is heard on strong stations the coupling cap to grid #1 on this tube may be leaky.
: : : Be sure the speaker cone isn't rubbing. Push lightly in different places on the speaker to see if this makes a difference.
: : : Norm
: : : : I'm working on a 1946 Crosley that has a 12A7 mixer, a 12Q7 detector, a 12SK7 IF amplifier, and a 50L6 audio output tube. The radio was a mess. I have had to replace much of the wiring in addition to the capacitors and many resistors. It had been lifeless until I replaced the audio output transformer. Now it works, but the sound is distorted: almost as if the sound is coming through water. The new audio output transformer I installed has a primary of 2,500 ohms and a secondary of 8 ohms. Voltage on all the tubes seems OK. As I said, all the capacitors, including the filter capacitors have been replaced. There is some hum, but not an extraordinary amount. I'm no longer sure where to look for problems. Any advice would be appreciated. One other question: I'm far from an expert at reading schematics, but it seems as if there are a couple of deviations between the factory wiring of this radio and the schematic. Is that possible, or is it more likely that I'm not reading it correctly? Any help would be appreciated.
: Looks like you might have -3.4 volts on pin #5 in relation to #8. If that's the case it's ok. A little low but won't cause distortion. .7 volts on 12SQ7 grid is ok. The resistor difference isn't a problem.
: Can you try a different speaker or check if the cone rubs? Is the distortion on all stations, strong and weak?
Thanks Norm and Don. You're right about the mixer, Don. It is a 12SA7. Norm, the schematic says to measure all voltages against pin 3 of the 12SK7, which it refers to as B-. When I do that, I get the positive voltage on the grid of the 50L6. It's negative, though, when measured against the plate of the 50L6. The distortion is on all stations, loud and weak. I hooked up another speaker, and the distortion stays. Does the 8 ohm impedance on the secondary of the output transformer seem OK to you?
: Not excactly sure what is meant when you measure against B- ? You mention 11.8 on pin #5 and 3.4 on pin #8. This makes pin #5 positive and will cause distortion..
: Norm
: : Hello, Norm. When you say to measure pin #5 in relation to pin #8, I believe you mean to put the tester leads on those pins. When I do that, I get -3.4 on pin 5 and 3.4 on pin 8. Measured against B-, I get 11.8 on pin 5 and 3.4 on pin 8. If I understand you right, that is what I would expect to get. I did notice that the load resistor is 420,000 ohms and the schematic says it should be 470,000. Does the voltage on the 50L6 sound correct? Pin 1 on the 12SQ7 has .7 volts. What do you think?
: : : Audio distortion is usually caused by a grid bias problem. Measure pin #5 in relation to pin #8 on your 50L6. Pin number 5 must be around 5 volts negative. If zero or positive you will have distortion. A leaky coupling cap, open resistor or bad 50L6 can cause this problem.
: : : 12Q7 or 12SQ7 must have near zero volts on grid #1. If distortion is heard on strong stations the coupling cap to grid #1 on this tube may be leaky.
: : : Be sure the speaker cone isn't rubbing. Push lightly in different places on the speaker to see if this makes a difference.
: : : Norm
: : : : I'm working on a 1946 Crosley that has a 12A7 mixer, a 12Q7 detector, a 12SK7 IF amplifier, and a 50L6 audio output tube. The radio was a mess. I have had to replace much of the wiring in addition to the capacitors and many resistors. It had been lifeless until I replaced the audio output transformer. Now it works, but the sound is distorted: almost as if the sound is coming through water. The new audio output transformer I installed has a primary of 2,500 ohms and a secondary of 8 ohms. Voltage on all the tubes seems OK. As I said, all the capacitors, including the filter capacitors have been replaced. There is some hum, but not an extraordinary amount. I'm no longer sure where to look for problems. Any advice would be appreciated. One other question: I'm far from an expert at reading schematics, but it seems as if there are a couple of deviations between the factory wiring of this radio and the schematic. Is that possible, or is it more likely that I'm not reading it correctly? Any help would be appreciated.
Think you have found the problem. Pin #5 of your 50L6 should not be positive. Even a few volts positive on this pin will cause distortion.
Pin #5 should have a capactior going to plate of 12SQ7 tube. It should also have a resistor, usually 470K, to B-. If the capacitor is leaky or resistor high in value voltage will be positive causing distortion. The 50L6 can also cause this problem.
Try a different 50L6 and check these components. If you don't have a spare tube install a lower value resistor to B- and see if sound quality improves. For test use 47K-100K.
Norm
: : Hi Mike
: : Looks like you might have -3.4 volts on pin #5 in relation to #8. If that's the case it's ok. A little low but won't cause distortion. .7 volts on 12SQ7 grid is ok. The resistor difference isn't a problem.
: : Can you try a different speaker or check if the cone rubs? Is the distortion on all stations, strong and weak?
: Thanks Norm and Don. You're right about the mixer, Don. It is a 12SA7. Norm, the schematic says to measure all voltages against pin 3 of the 12SK7, which it refers to as B-. When I do that, I get the positive voltage on the grid of the 50L6. It's negative, though, when measured against the plate of the 50L6. The distortion is on all stations, loud and weak. I hooked up another speaker, and the distortion stays. Does the 8 ohm impedance on the secondary of the output transformer seem OK to you?
: : Not excactly sure what is meant when you measure against B- ? You mention 11.8 on pin #5 and 3.4 on pin #8. This makes pin #5 positive and will cause distortion..
: : Norm
: : : Hello, Norm. When you say to measure pin #5 in relation to pin #8, I believe you mean to put the tester leads on those pins. When I do that, I get -3.4 on pin 5 and 3.4 on pin 8. Measured against B-, I get 11.8 on pin 5 and 3.4 on pin 8. If I understand you right, that is what I would expect to get. I did notice that the load resistor is 420,000 ohms and the schematic says it should be 470,000. Does the voltage on the 50L6 sound correct? Pin 1 on the 12SQ7 has .7 volts. What do you think?
: : : : Audio distortion is usually caused by a grid bias problem. Measure pin #5 in relation to pin #8 on your 50L6. Pin number 5 must be around 5 volts negative. If zero or positive you will have distortion. A leaky coupling cap, open resistor or bad 50L6 can cause this problem.
: : : : 12Q7 or 12SQ7 must have near zero volts on grid #1. If distortion is heard on strong stations the coupling cap to grid #1 on this tube may be leaky.
: : : : Be sure the speaker cone isn't rubbing. Push lightly in different places on the speaker to see if this makes a difference.
: : : : Norm
: : : : : I'm working on a 1946 Crosley that has a 12A7 mixer, a 12Q7 detector, a 12SK7 IF amplifier, and a 50L6 audio output tube. The radio was a mess. I have had to replace much of the wiring in addition to the capacitors and many resistors. It had been lifeless until I replaced the audio output transformer. Now it works, but the sound is distorted: almost as if the sound is coming through water. The new audio output transformer I installed has a primary of 2,500 ohms and a secondary of 8 ohms. Voltage on all the tubes seems OK. As I said, all the capacitors, including the filter capacitors have been replaced. There is some hum, but not an extraordinary amount. I'm no longer sure where to look for problems. Any advice would be appreciated. One other question: I'm far from an expert at reading schematics, but it seems as if there are a couple of deviations between the factory wiring of this radio and the schematic. Is that possible, or is it more likely that I'm not reading it correctly? Any help would be appreciated.