I was working on a 6 tube set that had a 35L6 audio output tube in it. I recapped the remaining wax caps in the set and then I burned in the set for 1 hour. I noticed that after appx 1/2 hour of operation the sets' audio began to distort. I had tested all the tubes in the set - they tested good! So I took them all out again and ran them for an extended period in the tester to see if the emission on any of them drooped with time. No - go!!. I also noticed that if I turned the set off for a brief period and then back on it started to work OK (probably not a resistor value change then causing a biasing issue). I then checked the B+ for signs of drooping with time - also no go.
So-o, I surmised that there may still be something wrong with the audio output tube. I inserted a 50L6 which was what I had on hand and an acceptable substitute for a 35L6 in series circuits according to the Cisin guide. Wouldnt you know it the set worked fine, even after 1 hour of play with plenty of audio!! It now sounds musical. Just goes to show that testers don't show ALL conditions, even with the tubes under some stress.
Lou
Output tubes can start to get leaky after heating. Most likely won't show on a tester.
Should be able to see the problem measuring voltage. Pin #5 must be around 5 volts negative in relation to pin #8. When it distorts this negative voltage will be gone and may actually become positive.
Problem can also be caused by a leaky coupling cap to pin #5 or increase in grid resistor.
Norm
:Heres' a good one...
:
:I was working on a 6 tube set that had a 35L6 audio output tube in it. I recapped the remaining wax caps in the set and then I burned in the set for 1 hour. I noticed that after appx 1/2 hour of operation the sets' audio began to distort. I had tested all the tubes in the set - they tested good! So I took them all out again and ran them for an extended period in the tester to see if the emission on any of them drooped with time. No - go!!. I also noticed that if I turned the set off for a brief period and then back on it started to work OK (probably not a resistor value change then causing a biasing issue). I then checked the B+ for signs of drooping with time - also no go.
:
:So-o, I surmised that there may still be something wrong with the audio output tube. I inserted a 50L6 which was what I had on hand and an acceptable substitute for a 35L6 in series circuits according to the Cisin guide. Wouldnt you know it the set worked fine, even after 1 hour of play with plenty of audio!! It now sounds musical. Just goes to show that testers don't show ALL conditions, even with the tubes under some stress.
:
:Lou
:
Since I replaced the caps I dont think we have a cap leakage problem. Also, since the problem disappeared with a new tube I think I know the answer. The "leakage with heating" issue is a new one for me.
Thanks
Lou
:Lou
:
: Output tubes can start to get leaky after heating. Most likely won't show on a tester.
:
: Should be able to see the problem measuring voltage. Pin #5 must be around 5 volts negative in relation to pin #8. When it distorts this negative voltage will be gone and may actually become positive.
:
: Problem can also be caused by a leaky coupling cap to pin #5 or increase in grid resistor.
:
:Norm
:
:
:
::Heres' a good one...
::
::I was working on a 6 tube set that had a 35L6 audio output tube in it. I recapped the remaining wax caps in the set and then I burned in the set for 1 hour. I noticed that after appx 1/2 hour of operation the sets' audio began to distort. I had tested all the tubes in the set - they tested good! So I took them all out again and ran them for an extended period in the tester to see if the emission on any of them drooped with time. No - go!!. I also noticed that if I turned the set off for a brief period and then back on it started to work OK (probably not a resistor value change then causing a biasing issue). I then checked the B+ for signs of drooping with time - also no go.
::
::So-o, I surmised that there may still be something wrong with the audio output tube. I inserted a 50L6 which was what I had on hand and an acceptable substitute for a 35L6 in series circuits according to the Cisin guide. Wouldnt you know it the set worked fine, even after 1 hour of play with plenty of audio!! It now sounds musical. Just goes to show that testers don't show ALL conditions, even with the tubes under some stress.
::
::Lou
::
:
:
All the Best,
Bill
:Thanks Norm
:
:Since I replaced the caps I dont think we have a cap leakage problem. Also, since the problem disappeared with a new tube I think I know the answer. The "leakage with heating" issue is a new one for me.
:
:Thanks
:Lou
:
:
::Lou
::
:: Output tubes can start to get leaky after heating. Most likely won't show on a tester.
::
:: Should be able to see the problem measuring voltage. Pin #5 must be around 5 volts negative in relation to pin #8. When it distorts this negative voltage will be gone and may actually become positive.
::
:: Problem can also be caused by a leaky coupling cap to pin #5 or increase in grid resistor.
::
::Norm
::
::
::
:::Heres' a good one...
:::
:::I was working on a 6 tube set that had a 35L6 audio output tube in it. I recapped the remaining wax caps in the set and then I burned in the set for 1 hour. I noticed that after appx 1/2 hour of operation the sets' audio began to distort. I had tested all the tubes in the set - they tested good! So I took them all out again and ran them for an extended period in the tester to see if the emission on any of them drooped with time. No - go!!. I also noticed that if I turned the set off for a brief period and then back on it started to work OK (probably not a resistor value change then causing a biasing issue). I then checked the B+ for signs of drooping with time - also no go.
:::
:::So-o, I surmised that there may still be something wrong with the audio output tube. I inserted a 50L6 which was what I had on hand and an acceptable substitute for a 35L6 in series circuits according to the Cisin guide. Wouldnt you know it the set worked fine, even after 1 hour of play with plenty of audio!! It now sounds musical. Just goes to show that testers don't show ALL conditions, even with the tubes under some stress.
:::
:::Lou
:::
::
::
:
:
Leakage was my way of saying grid is emitting. Either the tube is gassy or has other internal leakage from grid #1. If gassy grid one is in the ionization path between cathode and plate. This causes grid #1 to be slightly positive. Tube will draw excessive current and distort.
Heating over time causes this to worsen. Usually only found on output tubes due to their heating.
They won't show weak on a tester. Even if left in a tester most likely the tube will never heat enough. Might even show very high on a tester due to this leakage.
Norm
:Hi Lou and Norm,
: I have encountered this, too. Although I was told it had to do with poor emission, I never saw one of these show weak on a tube tester. I have even seen power output tubes that show weak on the tester sound fine in the radio.
: Once I had an Air Castle. Its power output tube was a 42. Audio never sounded right. I had a spare 42 but audio didn't improve when it was substituted.
: I sold it on eBay to a guy in Florida. It arrived with the type 42 broken, the only damage to the set. He promptly ordered an NOS 42 plugged it in and then raved about the audio quality.
: It seems I had two power output tubes bad in the same way!
: Then there was the clock radio, but I must not go on.
: So, norm, what is "Leakage with heating"? I have seen power output tubes get H-K shorts, but I suspect you mean something else.
:
:All the Best,
:
:Bill
::Thanks Norm
::
::Since I replaced the caps I dont think we have a cap leakage problem. Also, since the problem disappeared with a new tube I think I know the answer. The "leakage with heating" issue is a new one for me.
::
::Thanks
::Lou
::
::
:::Lou
:::
::: Output tubes can start to get leaky after heating. Most likely won't show on a tester.
:::
::: Should be able to see the problem measuring voltage. Pin #5 must be around 5 volts negative in relation to pin #8. When it distorts this negative voltage will be gone and may actually become positive.
:::
::: Problem can also be caused by a leaky coupling cap to pin #5 or increase in grid resistor.
:::
:::Norm
:::
:::
:::
::::Heres' a good one...
::::
::::I was working on a 6 tube set that had a 35L6 audio output tube in it. I recapped the remaining wax caps in the set and then I burned in the set for 1 hour. I noticed that after appx 1/2 hour of operation the sets' audio began to distort. I had tested all the tubes in the set - they tested good! So I took them all out again and ran them for an extended period in the tester to see if the emission on any of them drooped with time. No - go!!. I also noticed that if I turned the set off for a brief period and then back on it started to work OK (probably not a resistor value change then causing a biasing issue). I then checked the B+ for signs of drooping with time - also no go.
::::
::::So-o, I surmised that there may still be something wrong with the audio output tube. I inserted a 50L6 which was what I had on hand and an acceptable substitute for a 35L6 in series circuits according to the Cisin guide. Wouldnt you know it the set worked fine, even after 1 hour of play with plenty of audio!! It now sounds musical. Just goes to show that testers don't show ALL conditions, even with the tubes under some stress.
::::
::::Lou
::::
:::
:::
::
::
:
:
Don't filaments draw more current in a gassy tube?
All the Best,
Bill
:Bill
:
: Leakage was my way of saying grid is emitting. Either the tube is gassy or has other internal leakage from grid #1. If gassy grid one is in the ionization path between cathode and plate. This causes grid #1 to be slightly positive. Tube will draw excessive current and distort.
:
: Heating over time causes this to worsen. Usually only found on output tubes due to their heating.
:
: They won't show weak on a tester. Even if left in a tester most likely the tube will never heat enough. Might even show very high on a tester due to this leakage.
:
:Norm
:
:
:
::Hi Lou and Norm,
:: I have encountered this, too. Although I was told it had to do with poor emission, I never saw one of these show weak on a tube tester. I have even seen power output tubes that show weak on the tester sound fine in the radio.
:: Once I had an Air Castle. Its power output tube was a 42. Audio never sounded right. I had a spare 42 but audio didn't improve when it was substituted.
:: I sold it on eBay to a guy in Florida. It arrived with the type 42 broken, the only damage to the set. He promptly ordered an NOS 42 plugged it in and then raved about the audio quality.
:: It seems I had two power output tubes bad in the same way!
:: Then there was the clock radio, but I must not go on.
:: So, norm, what is "Leakage with heating"? I have seen power output tubes get H-K shorts, but I suspect you mean something else.
::
::All the Best,
::
::Bill
:::Thanks Norm
:::
:::Since I replaced the caps I dont think we have a cap leakage problem. Also, since the problem disappeared with a new tube I think I know the answer. The "leakage with heating" issue is a new one for me.
:::
:::Thanks
:::Lou
:::
:::
::::Lou
::::
:::: Output tubes can start to get leaky after heating. Most likely won't show on a tester.
::::
:::: Should be able to see the problem measuring voltage. Pin #5 must be around 5 volts negative in relation to pin #8. When it distorts this negative voltage will be gone and may actually become positive.
::::
:::: Problem can also be caused by a leaky coupling cap to pin #5 or increase in grid resistor.
::::
::::Norm
::::
::::
::::
:::::Heres' a good one...
:::::
:::::I was working on a 6 tube set that had a 35L6 audio output tube in it. I recapped the remaining wax caps in the set and then I burned in the set for 1 hour. I noticed that after appx 1/2 hour of operation the sets' audio began to distort. I had tested all the tubes in the set - they tested good! So I took them all out again and ran them for an extended period in the tester to see if the emission on any of them drooped with time. No - go!!. I also noticed that if I turned the set off for a brief period and then back on it started to work OK (probably not a resistor value change then causing a biasing issue). I then checked the B+ for signs of drooping with time - also no go.
:::::
:::::So-o, I surmised that there may still be something wrong with the audio output tube. I inserted a 50L6 which was what I had on hand and an acceptable substitute for a 35L6 in series circuits according to the Cisin guide. Wouldnt you know it the set worked fine, even after 1 hour of play with plenty of audio!! It now sounds musical. Just goes to show that testers don't show ALL conditions, even with the tubes under some stress.
:::::
:::::Lou
:::::
::::
::::
:::
:::
::
::
:
:
:Hi Norm,
: Thank you for the answer. It makes more sense now.
: I think it means that if the tube is slightly gassy, the grid will heat from ion bombardment, making it like a secondary cathode and taking it positive in relation to the real cathode.
: Alternatively a leak between grid 1 and grid 2 can do the same thing taking grid 1 positive and causing distortion.
: My tube tester may detect the first condition, but will never detect the gassy condition.
: Do I have it?
:
: Don't filaments draw more current in a gassy tube?
:
:All the Best,
:
:Bill
:
::Bill
::
:: Leakage was my way of saying grid is emitting. Either the tube is gassy or has other internal leakage from grid #1. If gassy grid one is in the ionization path between cathode and plate. This causes grid #1 to be slightly positive. Tube will draw excessive current and distort.
::
:: Heating over time causes this to worsen. Usually only found on output tubes due to their heating.
::
:: They won't show weak on a tester. Even if left in a tester most likely the tube will never heat enough. Might even show very high on a tester due to this leakage.
::
::Norm
::
::
::
:::Hi Lou and Norm,
::: I have encountered this, too. Although I was told it had to do with poor emission, I never saw one of these show weak on a tube tester. I have even seen power output tubes that show weak on the tester sound fine in the radio.
::: Once I had an Air Castle. Its power output tube was a 42. Audio never sounded right. I had a spare 42 but audio didn't improve when it was substituted.
::: I sold it on eBay to a guy in Florida. It arrived with the type 42 broken, the only damage to the set. He promptly ordered an NOS 42 plugged it in and then raved about the audio quality.
::: It seems I had two power output tubes bad in the same way!
::: Then there was the clock radio, but I must not go on.
::: So, norm, what is "Leakage with heating"? I have seen power output tubes get H-K shorts, but I suspect you mean something else.
:::
:::All the Best,
:::
:::Bill
::::Thanks Norm
::::
::::Since I replaced the caps I dont think we have a cap leakage problem. Also, since the problem disappeared with a new tube I think I know the answer. The "leakage with heating" issue is a new one for me.
::::
::::Thanks
::::Lou
::::
::::
:::::Lou
:::::
::::: Output tubes can start to get leaky after heating. Most likely won't show on a tester.
:::::
::::: Should be able to see the problem measuring voltage. Pin #5 must be around 5 volts negative in relation to pin #8. When it distorts this negative voltage will be gone and may actually become positive.
:::::
::::: Problem can also be caused by a leaky coupling cap to pin #5 or increase in grid resistor.
:::::
:::::Norm
:::::
:::::
:::::
::::::Heres' a good one...
::::::
::::::I was working on a 6 tube set that had a 35L6 audio output tube in it. I recapped the remaining wax caps in the set and then I burned in the set for 1 hour. I noticed that after appx 1/2 hour of operation the sets' audio began to distort. I had tested all the tubes in the set - they tested good! So I took them all out again and ran them for an extended period in the tester to see if the emission on any of them drooped with time. No - go!!. I also noticed that if I turned the set off for a brief period and then back on it started to work OK (probably not a resistor value change then causing a biasing issue). I then checked the B+ for signs of drooping with time - also no go.
::::::
::::::So-o, I surmised that there may still be something wrong with the audio output tube. I inserted a 50L6 which was what I had on hand and an acceptable substitute for a 35L6 in series circuits according to the Cisin guide. Wouldnt you know it the set worked fine, even after 1 hour of play with plenty of audio!! It now sounds musical. Just goes to show that testers don't show ALL conditions, even with the tubes under some stress.
::::::
::::::Lou
::::::
:::::
:::::
::::
::::
:::
:::
::
::
:
:
All the Best,
Bill
:I too have noticed that problem. But whatever is actually going bad inside the tube you can tell if it's bad by measuring the cathode voltage to gnd.
:Usually 5 or 6 volts ... when the tube is internally bad/leaky that cathode voltage will slowly start to creep upward.
:Distortion increases as it creeps up.
:
::Hi Norm,
:: Thank you for the answer. It makes more sense now.
:: I think it means that if the tube is slightly gassy, the grid will heat from ion bombardment, making it like a secondary cathode and taking it positive in relation to the real cathode.
:: Alternatively a leak between grid 1 and grid 2 can do the same thing taking grid 1 positive and causing distortion.
:: My tube tester may detect the first condition, but will never detect the gassy condition.
:: Do I have it?
::
:: Don't filaments draw more current in a gassy tube?
::
::All the Best,
::
::Bill
::
:::Bill
:::
::: Leakage was my way of saying grid is emitting. Either the tube is gassy or has other internal leakage from grid #1. If gassy grid one is in the ionization path between cathode and plate. This causes grid #1 to be slightly positive. Tube will draw excessive current and distort.
:::
::: Heating over time causes this to worsen. Usually only found on output tubes due to their heating.
:::
::: They won't show weak on a tester. Even if left in a tester most likely the tube will never heat enough. Might even show very high on a tester due to this leakage.
:::
:::Norm
:::
:::
:::
::::Hi Lou and Norm,
:::: I have encountered this, too. Although I was told it had to do with poor emission, I never saw one of these show weak on a tube tester. I have even seen power output tubes that show weak on the tester sound fine in the radio.
:::: Once I had an Air Castle. Its power output tube was a 42. Audio never sounded right. I had a spare 42 but audio didn't improve when it was substituted.
:::: I sold it on eBay to a guy in Florida. It arrived with the type 42 broken, the only damage to the set. He promptly ordered an NOS 42 plugged it in and then raved about the audio quality.
:::: It seems I had two power output tubes bad in the same way!
:::: Then there was the clock radio, but I must not go on.
:::: So, norm, what is "Leakage with heating"? I have seen power output tubes get H-K shorts, but I suspect you mean something else.
::::
::::All the Best,
::::
::::Bill
:::::Thanks Norm
:::::
:::::Since I replaced the caps I dont think we have a cap leakage problem. Also, since the problem disappeared with a new tube I think I know the answer. The "leakage with heating" issue is a new one for me.
:::::
:::::Thanks
:::::Lou
:::::
:::::
::::::Lou
::::::
:::::: Output tubes can start to get leaky after heating. Most likely won't show on a tester.
::::::
:::::: Should be able to see the problem measuring voltage. Pin #5 must be around 5 volts negative in relation to pin #8. When it distorts this negative voltage will be gone and may actually become positive.
::::::
:::::: Problem can also be caused by a leaky coupling cap to pin #5 or increase in grid resistor.
::::::
::::::Norm
::::::
::::::
::::::
:::::::Heres' a good one...
:::::::
:::::::I was working on a 6 tube set that had a 35L6 audio output tube in it. I recapped the remaining wax caps in the set and then I burned in the set for 1 hour. I noticed that after appx 1/2 hour of operation the sets' audio began to distort. I had tested all the tubes in the set - they tested good! So I took them all out again and ran them for an extended period in the tester to see if the emission on any of them drooped with time. No - go!!. I also noticed that if I turned the set off for a brief period and then back on it started to work OK (probably not a resistor value change then causing a biasing issue). I then checked the B+ for signs of drooping with time - also no go.
:::::::
:::::::So-o, I surmised that there may still be something wrong with the audio output tube. I inserted a 50L6 which was what I had on hand and an acceptable substitute for a 35L6 in series circuits according to the Cisin guide. Wouldnt you know it the set worked fine, even after 1 hour of play with plenty of audio!! It now sounds musical. Just goes to show that testers don't show ALL conditions, even with the tubes under some stress.
:::::::
:::::::Lou
:::::::
::::::
::::::
:::::
:::::
::::
::::
:::
:::
::
::
:
: