Sure Could Use Some Help Again With Static Problem

11/4/2008 10:44:15 AMJohnny

Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
Some of you good folks have helped with this one before.
I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.

11/4/2008 2:45:22 PMBill G.

:Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
:Some of you good folks have helped with this one before.
:I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
:So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
:All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
:
Hi Johnny,
Nice to here you are back again.

It sounds almost like your static goes away as long as some capacitor is charged up. I wonder if you got a wrong size of component when you recapped the radio. Often these schematics can be murky copys, and drop a decimal point or something. I have had this happen.

Best Regards,

Bill Grimm

11/4/2008 3:02:46 PMJohnny

::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
::Some of you good folks have helped with this one before.
::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
::
:Hi Johnny,
: Nice to here you are back again.
:
: It sounds almost like your static goes away as long as some capacitor is charged up. I wonder if you got a wrong size of component when you recapped the radio. Often these schematics can be murky copys, and drop a decimal point or something. I have had this happen.
:
:Best Regards,
:
:Bill Grimm
:
:Hey thanks Bill. I just got back. Went and bought a new cap and resistor. The schematic looks pretty clear as being a .1mfd but your idea may shed some light if these new parts don't fix it. If .1 is not correct which direction should I go? Upwards towards 1mfd or down towards .01mfd etc.?

11/4/2008 4:14:58 PMJohnny

::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
::Some of you good folks have helped with this one before.
::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
::
:Hi Johnny,
: Nice to here you are back again.
:
: It sounds almost like your static goes away as long as some capacitor is charged up. I wonder if you got a wrong size of component when you recapped the radio. Often these schematics can be murky copys, and drop a decimal point or something. I have had this happen.
:
:Best Regards,
:
:Bill Grimm
:
:It seems like the static is there when the .1mfd cap is charged and when I short it to ground and discharge it the static is gone until I turn the radio off for a while and then power it on again which allows the cap to recharge. Then static is there again until I short the cap to ground. The same little R/C circuit is on the 24 tube with the only difference being the resistor is a 10K instead of 40K.
Can you tell me what this little R/C circuit is actually doing on these two tubes?

11/4/2008 6:12:23 PMBob Z

I've had good luck using 'freeze spray' on questionable parts. Spraying it on the questionable resistor should cause the static to change, (come or go). It's worth a try and easy to do. Also works on noisy solder joints.

:::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
:::Some of you good folks have helped with this one before.
:::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
:::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
:::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
:::
::Hi Johnny,
:: Nice to here you are back again.
::
:: It sounds almost like your static goes away as long as some capacitor is charged up. I wonder if you got a wrong size of component when you recapped the radio. Often these schematics can be murky copys, and drop a decimal point or something. I have had this happen.
::
::Best Regards,
::
::Bill Grimm
::
::It seems like the static is there when the .1mfd cap is charged and when I short it to ground and discharge it the static is gone until I turn the radio off for a while and then power it on again which allows the cap to recharge. Then static is there again until I short the cap to ground. The same little R/C circuit is on the 24 tube with the only difference being the resistor is a 10K instead of 40K.
:Can you tell me what this little R/C circuit is actually doing on these two tubes?

11/4/2008 7:00:02 PMJohnny

:Thanks Bob but I tried that and it had no effect. I've replaced both the cap and resistor and it's still there. When I momentarilly short the tube side of the cap and resistor to ground the static is gone. Then it returns after the next power-on.
:
:I've had good luck using 'freeze spray' on questionable parts. Spraying it on the questionable resistor should cause the static to change, (come or go). It's worth a try and easy to do. Also works on noisy solder joints.
:
:
::::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
::::Some of you good folks have helped with this one before.
::::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
::::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
::::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
::::
:::Hi Johnny,
::: Nice to here you are back again.
:::
::: It sounds almost like your static goes away as long as some capacitor is charged up. I wonder if you got a wrong size of component when you recapped the radio. Often these schematics can be murky copys, and drop a decimal point or something. I have had this happen.
:::
:::Best Regards,
:::
:::Bill Grimm
:::
:::It seems like the static is there when the .1mfd cap is charged and when I short it to ground and discharge it the static is gone until I turn the radio off for a while and then power it on again which allows the cap to recharge. Then static is there again until I short the cap to ground. The same little R/C circuit is on the 24 tube with the only difference being the resistor is a 10K instead of 40K.
::Can you tell me what this little R/C circuit is actually doing on these two tubes?

11/6/2008 12:11:28 PMBill G.

:Can you tell me what this little R/C circuit
:is actually doing on these two tubes?

Hi Johnny,
The 40K resistor creates the DC bias for the 27. It causes the cathode of the 27 to go positive, making the grid to cathode voltage effectively negative. The negative bias is required for the type 27 to operate as a linear class A amplifier.
The capacitor across the 40K provides the AC/audio path to the tube so the audio won't be attenuated by the 40K resistor.

Best Regards,

Bill Grimm

11/6/2008 12:42:49 PMJohnny

::Can you tell me what this little R/C circuit
::is actually doing on these two tubes?
:
:Hi Johnny,
: The 40K resistor creates the DC bias for the 27. It causes the cathode of the 27 to go positive, making the grid to cathode voltage effectively negative. The negative bias is required for the type 27 to operate as a linear class A amplifier.
: The capacitor across the 40K provides the AC/audio path to the tube so the audio won't be attenuated by the 40K resistor.
:
:Best Regards,
:
:Bill Grimm
:
:Thanks Bill! That helps me to understand it a little better. I'm still reading my book on vavuum tube operation and I surely don't understand it all yet. As if I ever will.
Johnny

11/6/2008 3:15:07 PMBill G.

:::Can you tell me what this little R/C circuit
:::is actually doing on these two tubes?
::
::Hi Johnny,
:: The 40K resistor creates the DC bias for the 27. It causes the cathode of the 27 to go positive, making the grid to cathode voltage effectively negative. The negative bias is required for the type 27 to operate as a linear class A amplifier.
:: The capacitor across the 40K provides the AC/audio path to the tube so the audio won't be attenuated by the 40K resistor.
::
::Best Regards,
::
::Bill Grimm
::
::Thanks Bill! That helps me to understand it a little better. I'm still reading my book on vavuum tube operation and I surely don't understand it all yet. As if I ever will.
:Johnny

Hi Johnny,
I have looked over the schematic and think we need to do more troubleshooting before you start pulling audio transformers and other components.
Try this. Disconnect the grid of the 27, and connect it to ground throught a resistor of around 470 ohms. 100 to 1K should do.
Turn it on and listen. If you still have noise then you have to go back to troubleshooting the audio section. I suspect that you will not hear noise, though, since you have been through the audio section with a fine tooth comb.
If the noise is still is gone, restore the 27's grid connection and give the same treatment to the previous stage.
At some point you will get the noise back. This will point to the noisy stage of amplification.

I am thinking that you may have current leakage from primary to secondary in an IF transformer or the oscillator coil. I suspect this because you have been through the accessable components and have not been in the IFs. Where else can the problem be hiding?

Best Regards,

Bill Grimm

11/6/2008 8:20:44 PMJohnny

::::Can you tell me what this little R/C circuit
::::is actually doing on these two tubes?
:::
:::Hi Johnny,
::: The 40K resistor creates the DC bias for the 27. It causes the cathode of the 27 to go positive, making the grid to cathode voltage effectively negative. The negative bias is required for the type 27 to operate as a linear class A amplifier.
::: The capacitor across the 40K provides the AC/audio path to the tube so the audio won't be attenuated by the 40K resistor.
:::
:::Best Regards,
:::
:::Bill Grimm
:::
:::Thanks Bill! That helps me to understand it a little better. I'm still reading my book on vavuum tube operation and I surely don't understand it all yet. As if I ever will.
::Johnny
:
:Hi Johnny,
: I have looked over the schematic and think we need to do more troubleshooting before you start pulling audio transformers and other components.
: Try this. Disconnect the grid of the 27, and connect it to ground throught a resistor of around 470 ohms. 100 to 1K should do.
: Turn it on and listen. If you still have noise then you have to go back to troubleshooting the audio section. I suspect that you will not hear noise, though, since you have been through the audio section with a fine tooth comb.
: If the noise is still is gone, restore the 27's grid connection and give the same treatment to the previous stage.
: At some point you will get the noise back. This will point to the noisy stage of amplification.
:
: I am thinking that you may have current leakage from primary to secondary in an IF transformer or the oscillator coil. I suspect this because you have been through the accessable components and have not been in the IFs. Where else can the problem be hiding?
:
:Best Regards,
:
:Bill Grimm
:
:Thanks Bill! A whole new direction to go in. I think that's just what I needed. I printed this out so I follow it to the "T". It's late in the day here so I will perform these tests first thing in the morning. Hopefully not 1am again. I actually opened up the 1st IF transformer today checking for poor solder etc. Thanks again!
Johnny

11/7/2008 9:43:58 AMBill G.

Hi Johnny,
Another thougth came to mind. Do other AM radios in your house have this problem?
Switching power supplies are very common now a days. They can put significant electronic noise on to the AM band.
If your other radios receive good clean signals, this is a red herring, but if not, it is your answer.

Best Regards,

Bill Grimm

11/7/2008 11:01:29 AMrob

he claims he can drain off a cap and it goes away for a bit. seems like its in the radio somewhere

:Hi Johnny,
: Another thougth came to mind. Do other AM radios in your house have this problem?
: Switching power supplies are very common now a days. They can put significant electronic noise on to the AM band.
: If your other radios receive good clean signals, this is a red herring, but if not, it is your answer.
:
:Best Regards,
:
:Bill Grimm

11/7/2008 12:33:31 PMBill G.

:he claims he can drain off a cap and it goes away for a bit. seems like its in the radio somewhere
:
Hi Rob,
Good point, if the audio stays.

Best Regards,

Bill Grimm

11/7/2008 1:13:00 PMJohnny

:Good morning Bill. I removed the 27 grid and grounded it thru a 390 ohm 1 watt and I still have static. Did I do this right? The grid wire I grounded is the wire coming from the IF transformer just to the left of the 27 tube on the schematic. Shows as a squigly line at the 9 o'clock position on the 27 tube.
:
::he claims he can drain off a cap and it goes away for a bit. seems like its in the radio somewhere
::
:Hi Rob,
: Good point, if the audio stays.
:
:Best Regards,
:
:Bill Grimm

11/7/2008 1:57:13 PMBill G.

::Good morning Bill. I removed the 27 grid and grounded it thru a 390 ohm 1 watt and I still have static. Did I do this right? The grid wire I grounded is the wire coming from the IF transformer just to the left of the 27 tube on the schematic. Shows as a squigly line at the 9 o'clock position on the 27 tube.
::
:::he claims he can drain off a cap and it goes away for a bit. seems like its in the radio somewhere
:::
::Hi Rob,
:: Good point, if the audio stays.
::
::Best Regards,
::
::Bill Grimm

Hi Johnny,
The description of what you did sounds perfect, although the result is not what I would have expected.
Leave the resistor there. You could have two causes to the problem, with the other further up. This indicates you really have a problem in your audio section, as you had thought.
My experience has been that when you look this hard in a section for the problem it is somewhere else. Not the case this time!

You should now be able to pull the 51's, 24, and other 27 and this would have no effect since the RF and IF are isolated.
One quick test, you may have done already, is to turn out the lights and look for blue glow in the remaining tubes. This is an idication of gas. the only early 1930's Airline I ever did had a gassy 80, showing blue around the filament. Its problem was audio noise, too.
Also check the tube connections to the pins. This can be done by ohm meter or by checking wilth a volt meter with the set on. These 5 and 6 pin sockets weren't nearly as reliable octal.

I will keep thinking about it. Keep us posted.

Best Regards,

Bill Grimm

11/7/2008 2:16:42 PMJohnny

:::Good morning Bill. I removed the 27 grid and grounded it thru a 390 ohm 1 watt and I still have static. Did I do this right? The grid wire I grounded is the wire coming from the IF transformer just to the left of the 27 tube on the schematic. Shows as a squigly line at the 9 o'clock position on the 27 tube.
:::
::::he claims he can drain off a cap and it goes away for a bit. seems like its in the radio somewhere
::::
:::Hi Rob,
::: Good point, if the audio stays.
:::
:::Best Regards,
:::
:::Bill Grimm
:
:Hi Johnny,
: The description of what you did sounds perfect, although the result is not what I would have expected.
: Leave the resistor there. You could have two causes to the problem, with the other further up. This indicates you really have a problem in your audio section, as you had thought.
: My experience has been that when you look this hard in a section for the problem it is somewhere else. Not the case this time!
:
: You should now be able to pull the 51's, 24, and other 27 and this would have no effect since the RF and IF are isolated.
: One quick test, you may have done already, is to turn out the lights and look for blue glow in the remaining tubes. This is an idication of gas. the only early 1930's Airline I ever did had a gassy 80, showing blue around the filament. Its problem was audio noise, too.
: Also check the tube connections to the pins. This can be done by ohm meter or by checking wilth a volt meter with the set on. These 5 and 6 pin sockets weren't nearly as reliable octal.
:
: I will keep thinking about it. Keep us posted.
:
:Best Regards,
:
:Bill Grimm
:
:I will check for gas first. And then are you saying to take the 51's, 24 and 27 tubes out of the radio and see if noise is still there?

11/7/2008 3:38:25 PMBill G.

::::Good morning Bill. I removed the 27 grid and grounded it thru a 390 ohm 1 watt and I still have static. Did I do this right? The grid wire I grounded is the wire coming from the IF transformer just to the left of the 27 tube on the schematic. Shows as a squigly line at the 9 o'clock position on the 27 tube.
::::
:::::he claims he can drain off a cap and it goes away for a bit. seems like its in the radio somewhere
:::::
::::Hi Rob,
:::: Good point, if the audio stays.
::::
::::Best Regards,
::::
::::Bill Grimm
::
::Hi Johnny,
:: The description of what you did sounds perfect, although the result is not what I would have expected.
:: Leave the resistor there. You could have two causes to the problem, with the other further up. This indicates you really have a problem in your audio section, as you had thought.
:: My experience has been that when you look this hard in a section for the problem it is somewhere else. Not the case this time!
::
:: You should now be able to pull the 51's, 24, and other 27 and this would have no effect since the RF and IF are isolated.
:: One quick test, you may have done already, is to turn out the lights and look for blue glow in the remaining tubes. This is an idication of gas. the only early 1930's Airline I ever did had a gassy 80, showing blue around the filament. Its problem was audio noise, too.
:: Also check the tube connections to the pins. This can be done by ohm meter or by checking wilth a volt meter with the set on. These 5 and 6 pin sockets weren't nearly as reliable octal.
::
:: I will keep thinking about it. Keep us posted.
::
::Best Regards,
::
::Bill Grimm
::
::I will check for gas first. And then are you saying to take the 51's, 24 and 27 tubes out of the radio and see if noise is still there?

Yes. Order doesn't matter.

Best Regards,
Bill

11/9/2008 8:30:11 PMJohnny

:Hi Bill. Well I did the tube pulling and it's still there. I keep going back to that RFC coil. When the static is there I can tap on, pry on, push on it etc. and the static gets worse, better, and everything in between. Then when I ground it the static goes away for a while. I'm gonna try to determine what the values of that RFC are and try replacing it before I go any further. You've been very much help through all this troubleshooting and it really is appreciated. I'll let you know how things turn out.
Johnny
:
:::::Good morning Bill. I removed the 27 grid and grounded it thru a 390 ohm 1 watt and I still have static. Did I do this right? The grid wire I grounded is the wire coming from the IF transformer just to the left of the 27 tube on the schematic. Shows as a squigly line at the 9 o'clock position on the 27 tube.
:::::
::::::he claims he can drain off a cap and it goes away for a bit. seems like its in the radio somewhere
::::::
:::::Hi Rob,
::::: Good point, if the audio stays.
:::::
:::::Best Regards,
:::::
:::::Bill Grimm
:::
:::Hi Johnny,
::: The description of what you did sounds perfect, although the result is not what I would have expected.
::: Leave the resistor there. You could have two causes to the problem, with the other further up. This indicates you really have a problem in your audio section, as you had thought.
::: My experience has been that when you look this hard in a section for the problem it is somewhere else. Not the case this time!
:::
::: You should now be able to pull the 51's, 24, and other 27 and this would have no effect since the RF and IF are isolated.
::: One quick test, you may have done already, is to turn out the lights and look for blue glow in the remaining tubes. This is an idication of gas. the only early 1930's Airline I ever did had a gassy 80, showing blue around the filament. Its problem was audio noise, too.
::: Also check the tube connections to the pins. This can be done by ohm meter or by checking wilth a volt meter with the set on. These 5 and 6 pin sockets weren't nearly as reliable octal.
:::
::: I will keep thinking about it. Keep us posted.
:::
:::Best Regards,
:::
:::Bill Grimm
:::
:::I will check for gas first. And then are you saying to take the 51's, 24 and 27 tubes out of the radio and see if noise is still there?
:
:Yes. Order doesn't matter.
:
:Best Regards,
:Bill

11/10/2008 5:48:11 PMJohnny

:Hi Bill. Well I don't know if pulling the tubes was a good idea. I pulled the 27 detector and the static is gone. Pulled the 27 oscillator and the static stays. Pulled the 24 tube and there was a low pop from the speaker. No static but now the radio doesn't work at all. Powers up, lamp comes on but nothing else. I don't see any components visibly blown so I guess I'll check the rest of the tubes now. Power was off when I pulled the individual tubes and then back on when the tube was out to check for noise. Don't know what might have happened now.
Johnny
:
:::::Good morning Bill. I removed the 27 grid and grounded it thru a 390 ohm 1 watt and I still have static. Did I do this right? The grid wire I grounded is the wire coming from the IF transformer just to the left of the 27 tube on the schematic. Shows as a squigly line at the 9 o'clock position on the 27 tube.
:::::
::::::he claims he can drain off a cap and it goes away for a bit. seems like its in the radio somewhere
::::::
:::::Hi Rob,
::::: Good point, if the audio stays.
:::::
:::::Best Regards,
:::::
:::::Bill Grimm
:::
:::Hi Johnny,
::: The description of what you did sounds perfect, although the result is not what I would have expected.
::: Leave the resistor there. You could have two causes to the problem, with the other further up. This indicates you really have a problem in your audio section, as you had thought.
::: My experience has been that when you look this hard in a section for the problem it is somewhere else. Not the case this time!
:::
::: You should now be able to pull the 51's, 24, and other 27 and this would have no effect since the RF and IF are isolated.
::: One quick test, you may have done already, is to turn out the lights and look for blue glow in the remaining tubes. This is an idication of gas. the only early 1930's Airline I ever did had a gassy 80, showing blue around the filament. Its problem was audio noise, too.
::: Also check the tube connections to the pins. This can be done by ohm meter or by checking wilth a volt meter with the set on. These 5 and 6 pin sockets weren't nearly as reliable octal.
:::
::: I will keep thinking about it. Keep us posted.
:::
:::Best Regards,
:::
:::Bill Grimm
:::
:::I will check for gas first. And then are you saying to take the 51's, 24 and 27 tubes out of the radio and see if noise is still there?
:
:Yes. Order doesn't matter.
:
:Best Regards,
:Bill

11/7/2008 1:40:22 PMJohnny

11/7/2008 4:04:08 PMRadiodoc

Johnny,

I think you mentioned you had an oscilloscope. When the radio is making the noise check at the junction of the .5 cap, driver tranny B+ lead and 75000 Ohm resistor for an indication that matches the sound from the speaker. The 75K resistor may be causing noise if it hasn't been replaced. If there is nothing there, then try disconnecting the B+ lead of the driver tranny and see if the noise is heard in the speaker. If it still is heard, there may be a problem with the secondary of the driver tranny.

Radiodoc
******************

::Hi Johnny,
:: Another thougth came to mind. Do other AM radios in your house have this problem?
:: Switching power supplies are very common now a days. They can put significant electronic noise on to the AM band.
:: If your other radios receive good clean signals, this is a red herring, but if not, it is your answer.
::
::Best Regards,
::
::Bill Grimm
::
::No to this question. The other radios do not have the problem even while in the same proximity as the one we're testing.

11/9/2008 8:23:54 PMJohnny

:Thanks Doc! I've performed those test earlier. Now I'm convenced the problem is with that RFC coil.
:
:Johnny,
:
:I think you mentioned you had an oscilloscope. When the radio is making the noise check at the junction of the .5 cap, driver tranny B+ lead and 75000 Ohm resistor for an indication that matches the sound from the speaker. The 75K resistor may be causing noise if it hasn't been replaced. If there is nothing there, then try disconnecting the B+ lead of the driver tranny and see if the noise is heard in the speaker. If it still is heard, there may be a problem with the secondary of the driver tranny.
:
:Radiodoc
:******************
:
:
:::Hi Johnny,
::: Another thougth came to mind. Do other AM radios in your house have this problem?
::: Switching power supplies are very common now a days. They can put significant electronic noise on to the AM band.
::: If your other radios receive good clean signals, this is a red herring, but if not, it is your answer.
:::
:::Best Regards,
:::
:::Bill Grimm
:::
:::No to this question. The other radios do not have the problem even while in the same proximity as the one we're testing.

11/4/2008 9:40:15 PMharold

11/5/2008 7:25:48 AMGary W. Prutchick

Johnny,

Try this simple test:
Disconnect one side of the .1 uf (cathode bypass capacitor) and see if the static stops. The audio output should decrease but if the static stops it indicates that the capacitor is breaking down and needs replacing.

Gary

11/5/2008 7:39:59 AMJohnny

:Thanks Gary! Couldn't sleep so I've been up all night on this thing. I'll try that right now however it was a new cap and I replaced that with another new cap.
:
:Johnny,
:
:Try this simple test:
:Disconnect one side of the .1 uf (cathode bypass capacitor) and see if the static stops. The audio output should decrease but if the static stops it indicates that the capacitor is breaking down and needs replacing.
:
:Gary
:
:
:
::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
::Some of you good folks have helped with this one before.
::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
::

11/5/2008 8:40:10 AMJohnny

:Okay. Yes the volume is all but gone as expected and I don't hear the static and I'm not seeing it on the o-scope. The schematic looks like the cap is called out as a .1mfd but could this be wrong? I never powered the radio up when I got it. Just replaced all the caps. This is the second new cap I've tried and it makes no difference. I even replaced the 40K resistor. If I did try a different value on the cap which way should I go? From .1 towards 1 or towards .01? I've checked all associated components that I see the static on with my scope and I'm just not finding anything. I've even swapped out tubes. Let me define this static. It's not static like you might associate with "snow" on a TV set it's more of a "snap-crackle-pop" with no real frequency to it. Does this help?
:
:Johnny,
:
:Try this simple test:
:Disconnect one side of the .1 uf (cathode bypass capacitor) and see if the static stops. The audio output should decrease but if the static stops it indicates that the capacitor is breaking down and needs replacing.
:
:Gary
:
:
:
::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
::Some of you good folks have helped with this one before.
::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
::

11/5/2008 8:52:44 AMGary W. Prutchick

Next test:

Re-connect the cathode bypass capacitor then connect a .1 uf capacitor (temporay) from the grid of the 27 to ground. If the static goes away the problem is before the det/audio stage.

Gary
::Okay. Yes the volume is all but gone as expected and I don't hear the static and I'm not seeing it on the o-scope. The schematic looks like the cap is called out as a .1mfd but could this be wrong? I never powered the radio up when I got it. Just replaced all the caps. This is the second new cap I've tried and it makes no difference. I even replaced the 40K resistor. If I did try a different value on the cap which way should I go? From .1 towards 1 or towards .01? I've checked all associated components that I see the static on with my scope and I'm just not finding anything. I've even swapped out tubes. Let me define this static. It's not static like you might associate with "snow" on a TV set it's more of a "snap-crackle-pop" with no real frequency to it. Does this help?
::
::Johnny,
::
::Try this simple test:
::Disconnect one side of the .1 uf (cathode bypass capacitor) and see if the static stops. The audio output should decrease but if the static stops it indicates that the capacitor is breaking down and needs replacing.
::
::Gary
::
::
::
:::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
:::Some of you good folks have helped with this one before.
:::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
:::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
:::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
:::

11/5/2008 9:14:29 AMJohnny

:Okay did that Gary and the static is still there. Volume also went completely away with that test. Sure appreciate this help. Johnny
:
:Next test:
:
:Re-connect the cathode bypass capacitor then connect a .1 uf capacitor (temporay) from the grid of the 27 to ground. If the static goes away the problem is before the det/audio stage.
:
:Gary
:::Okay. Yes the volume is all but gone as expected and I don't hear the static and I'm not seeing it on the o-scope. The schematic looks like the cap is called out as a .1mfd but could this be wrong? I never powered the radio up when I got it. Just replaced all the caps. This is the second new cap I've tried and it makes no difference. I even replaced the 40K resistor. If I did try a different value on the cap which way should I go? From .1 towards 1 or towards .01? I've checked all associated components that I see the static on with my scope and I'm just not finding anything. I've even swapped out tubes. Let me define this static. It's not static like you might associate with "snow" on a TV set it's more of a "snap-crackle-pop" with no real frequency to it. Does this help?
:::
:::Johnny,
:::
:::Try this simple test:
:::Disconnect one side of the .1 uf (cathode bypass capacitor) and see if the static stops. The audio output should decrease but if the static stops it indicates that the capacitor is breaking down and needs replacing.
:::
:::Gary
:::
:::
:::
::::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
::::Some of you good folks have helped with this one before.
::::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
::::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
::::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
::::

11/5/2008 9:37:40 AMGary W. Prutchick

Ok, next, is the static there when the volume control is at minimum?

Gary

::Okay did that Gary and the static is still there. Volume also went completely away with that test. Sure appreciate this help. Johnny
::
::Next test:
::
::Re-connect the cathode bypass capacitor then connect a .1 uf capacitor (temporay) from the grid of the 27 to ground. If the static goes away the problem is before the det/audio stage.
::
::Gary
::::Okay. Yes the volume is all but gone as expected and I don't hear the static and I'm not seeing it on the o-scope. The schematic looks like the cap is called out as a .1mfd but could this be wrong? I never powered the radio up when I got it. Just replaced all the caps. This is the second new cap I've tried and it makes no difference. I even replaced the 40K resistor. If I did try a different value on the cap which way should I go? From .1 towards 1 or towards .01? I've checked all associated components that I see the static on with my scope and I'm just not finding anything. I've even swapped out tubes. Let me define this static. It's not static like you might associate with "snow" on a TV set it's more of a "snap-crackle-pop" with no real frequency to it. Does this help?
::::
::::Johnny,
::::
::::Try this simple test:
::::Disconnect one side of the .1 uf (cathode bypass capacitor) and see if the static stops. The audio output should decrease but if the static stops it indicates that the capacitor is breaking down and needs replacing.
::::
::::Gary
::::
::::
::::
:::::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
:::::Some of you good folks have helped with this one before.
:::::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
:::::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
:::::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
:::::

11/5/2008 10:06:30 AMJohnny

:The static is constant and is not affected by the volume or tone control pots. There at min. or max. and everywhere in between.
:
:Ok, next, is the static there when the volume control is at minimum?
:
:Gary
:
:
:::Okay did that Gary and the static is still there. Volume also went completely away with that test. Sure appreciate this help. Johnny
:::
:::Next test:
:::
:::Re-connect the cathode bypass capacitor then connect a .1 uf capacitor (temporay) from the grid of the 27 to ground. If the static goes away the problem is before the det/audio stage.
:::
:::Gary
:::::Okay. Yes the volume is all but gone as expected and I don't hear the static and I'm not seeing it on the o-scope. The schematic looks like the cap is called out as a .1mfd but could this be wrong? I never powered the radio up when I got it. Just replaced all the caps. This is the second new cap I've tried and it makes no difference. I even replaced the 40K resistor. If I did try a different value on the cap which way should I go? From .1 towards 1 or towards .01? I've checked all associated components that I see the static on with my scope and I'm just not finding anything. I've even swapped out tubes. Let me define this static. It's not static like you might associate with "snow" on a TV set it's more of a "snap-crackle-pop" with no real frequency to it. Does this help?
:::::
:::::Johnny,
:::::
:::::Try this simple test:
:::::Disconnect one side of the .1 uf (cathode bypass capacitor) and see if the static stops. The audio output should decrease but if the static stops it indicates that the capacitor is breaking down and needs replacing.
:::::
:::::Gary
:::::
:::::
:::::
::::::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
::::::Some of you good folks have helped with this one before.
::::::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
::::::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
::::::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
::::::

11/5/2008 10:32:42 AMGary W. Prutchick

Momentarily short out the RFC. Does the static go away?

::The static is constant and is not affected by the volume or tone control pots. There at min. or max. and everywhere in between.
::
::Ok, next, is the static there when the volume control is at minimum?
::
::Gary
::
::
::::Okay did that Gary and the static is still there. Volume also went completely away with that test. Sure appreciate this help. Johnny
::::
::::Next test:
::::
::::Re-connect the cathode bypass capacitor then connect a .1 uf capacitor (temporay) from the grid of the 27 to ground. If the static goes away the problem is before the det/audio stage.
::::
::::Gary
::::::Okay. Yes the volume is all but gone as expected and I don't hear the static and I'm not seeing it on the o-scope. The schematic looks like the cap is called out as a .1mfd but could this be wrong? I never powered the radio up when I got it. Just replaced all the caps. This is the second new cap I've tried and it makes no difference. I even replaced the 40K resistor. If I did try a different value on the cap which way should I go? From .1 towards 1 or towards .01? I've checked all associated components that I see the static on with my scope and I'm just not finding anything. I've even swapped out tubes. Let me define this static. It's not static like you might associate with "snow" on a TV set it's more of a "snap-crackle-pop" with no real frequency to it. Does this help?
::::::
::::::Johnny,
::::::
::::::Try this simple test:
::::::Disconnect one side of the .1 uf (cathode bypass capacitor) and see if the static stops. The audio output should decrease but if the static stops it indicates that the capacitor is breaking down and needs replacing.
::::::
::::::Gary
::::::
::::::
::::::
:::::::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
:::::::Some of you good folks have helped with this one before.
:::::::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
:::::::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
:::::::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
:::::::

11/5/2008 10:42:11 AMJohnny

:When I short the RFC the static goes away for a while then comes back. When I first noticed this problem I found that one of the RFC leads was very close to the chassis and arcing to it. I reworked all that and the static went away. The radio has been off for about a month and when I fired it up yesterday the static was back. This RFC is a coil about 1" in diameter and a 1/4" thick and is mounted with a screw and nut to the chassis. Looks original and it looks good. Not frayed, broken etc.
:
:Momentarily short out the RFC. Does the static go away?
:
:::The static is constant and is not affected by the volume or tone control pots. There at min. or max. and everywhere in between.
:::
:::Ok, next, is the static there when the volume control is at minimum?
:::
:::Gary
:::
:::
:::::Okay did that Gary and the static is still there. Volume also went completely away with that test. Sure appreciate this help. Johnny
:::::
:::::Next test:
:::::
:::::Re-connect the cathode bypass capacitor then connect a .1 uf capacitor (temporay) from the grid of the 27 to ground. If the static goes away the problem is before the det/audio stage.
:::::
:::::Gary
:::::::Okay. Yes the volume is all but gone as expected and I don't hear the static and I'm not seeing it on the o-scope. The schematic looks like the cap is called out as a .1mfd but could this be wrong? I never powered the radio up when I got it. Just replaced all the caps. This is the second new cap I've tried and it makes no difference. I even replaced the 40K resistor. If I did try a different value on the cap which way should I go? From .1 towards 1 or towards .01? I've checked all associated components that I see the static on with my scope and I'm just not finding anything. I've even swapped out tubes. Let me define this static. It's not static like you might associate with "snow" on a TV set it's more of a "snap-crackle-pop" with no real frequency to it. Does this help?
:::::::
:::::::Johnny,
:::::::
:::::::Try this simple test:
:::::::Disconnect one side of the .1 uf (cathode bypass capacitor) and see if the static stops. The audio output should decrease but if the static stops it indicates that the capacitor is breaking down and needs replacing.
:::::::
:::::::Gary
:::::::
:::::::
:::::::
::::::::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
::::::::Some of you good folks have helped with this one before.
::::::::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
::::::::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
::::::::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
::::::::

11/5/2008 11:26:03 AMGary W. Prutchick

Have you tried tapping tubes, components, and solder joints, or moving wires around etc? This may be a mecahnical problem, wire shorting to the chassis, cold solder joint, dirty tube socket.

Gary

::When I short the RFC the static goes away for a while then comes back. When I first noticed this problem I found that one of the RFC leads was very close to the chassis and arcing to it. I reworked all that and the static went away. The radio has been off for about a month and when I fired it up yesterday the static was back. This RFC is a coil about 1" in diameter and a 1/4" thick and is mounted with a screw and nut to the chassis. Looks original and it looks good. Not frayed, broken etc.
::
::Momentarily short out the RFC. Does the static go away?
::
::::The static is constant and is not affected by the volume or tone control pots. There at min. or max. and everywhere in between.
::::
::::Ok, next, is the static there when the volume control is at minimum?
::::
::::Gary
::::
::::
::::::Okay did that Gary and the static is still there. Volume also went completely away with that test. Sure appreciate this help. Johnny
::::::
::::::Next test:
::::::
::::::Re-connect the cathode bypass capacitor then connect a .1 uf capacitor (temporay) from the grid of the 27 to ground. If the static goes away the problem is before the det/audio stage.
::::::
::::::Gary
::::::::Okay. Yes the volume is all but gone as expected and I don't hear the static and I'm not seeing it on the o-scope. The schematic looks like the cap is called out as a .1mfd but could this be wrong? I never powered the radio up when I got it. Just replaced all the caps. This is the second new cap I've tried and it makes no difference. I even replaced the 40K resistor. If I did try a different value on the cap which way should I go? From .1 towards 1 or towards .01? I've checked all associated components that I see the static on with my scope and I'm just not finding anything. I've even swapped out tubes. Let me define this static. It's not static like you might associate with "snow" on a TV set it's more of a "snap-crackle-pop" with no real frequency to it. Does this help?
::::::::
::::::::Johnny,
::::::::
::::::::Try this simple test:
::::::::Disconnect one side of the .1 uf (cathode bypass capacitor) and see if the static stops. The audio output should decrease but if the static stops it indicates that the capacitor is breaking down and needs replacing.
::::::::
::::::::Gary
::::::::
::::::::
::::::::
:::::::::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
:::::::::Some of you good folks have helped with this one before.
:::::::::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
:::::::::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
:::::::::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
:::::::::

11/5/2008 11:33:57 AMJohnny

:Yeah I've done all that groovy stuff but I might as well go through it again. I'll let ya know. Thanks Gary!
:
:Have you tried tapping tubes, components, and solder joints, or moving wires around etc? This may be a mecahnical problem, wire shorting to the chassis, cold solder joint, dirty tube socket.
:
:Gary
:
:::When I short the RFC the static goes away for a while then comes back. When I first noticed this problem I found that one of the RFC leads was very close to the chassis and arcing to it. I reworked all that and the static went away. The radio has been off for about a month and when I fired it up yesterday the static was back. This RFC is a coil about 1" in diameter and a 1/4" thick and is mounted with a screw and nut to the chassis. Looks original and it looks good. Not frayed, broken etc.
:::
:::Momentarily short out the RFC. Does the static go away?
:::
:::::The static is constant and is not affected by the volume or tone control pots. There at min. or max. and everywhere in between.
:::::
:::::Ok, next, is the static there when the volume control is at minimum?
:::::
:::::Gary
:::::
:::::
:::::::Okay did that Gary and the static is still there. Volume also went completely away with that test. Sure appreciate this help. Johnny
:::::::
:::::::Next test:
:::::::
:::::::Re-connect the cathode bypass capacitor then connect a .1 uf capacitor (temporay) from the grid of the 27 to ground. If the static goes away the problem is before the det/audio stage.
:::::::
:::::::Gary
:::::::::Okay. Yes the volume is all but gone as expected and I don't hear the static and I'm not seeing it on the o-scope. The schematic looks like the cap is called out as a .1mfd but could this be wrong? I never powered the radio up when I got it. Just replaced all the caps. This is the second new cap I've tried and it makes no difference. I even replaced the 40K resistor. If I did try a different value on the cap which way should I go? From .1 towards 1 or towards .01? I've checked all associated components that I see the static on with my scope and I'm just not finding anything. I've even swapped out tubes. Let me define this static. It's not static like you might associate with "snow" on a TV set it's more of a "snap-crackle-pop" with no real frequency to it. Does this help?
:::::::::
:::::::::Johnny,
:::::::::
:::::::::Try this simple test:
:::::::::Disconnect one side of the .1 uf (cathode bypass capacitor) and see if the static stops. The audio output should decrease but if the static stops it indicates that the capacitor is breaking down and needs replacing.
:::::::::
:::::::::Gary
:::::::::
:::::::::
:::::::::
::::::::::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
::::::::::Some of you good folks have helped with this one before.
::::::::::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
::::::::::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
::::::::::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
::::::::::

11/5/2008 12:03:27 PMGary W. Prutchicik

A few more suggestions:

Disconnect the .001 uf cap on the plate of the 27, static gone?

Disconnect, the .5 uf capacitor on the audio transformer, static gone?

Gary

:
::Yeah I've done all that groovy stuff but I might as well go through it again. I'll let ya know. Thanks Gary!
::
::Have you tried tapping tubes, components, and solder joints, or moving wires around etc? This may be a mecahnical problem, wire shorting to the chassis, cold solder joint, dirty tube socket.
::
::Gary
::
::::When I short the RFC the static goes away for a while then comes back. When I first noticed this problem I found that one of the RFC leads was very close to the chassis and arcing to it. I reworked all that and the static went away. The radio has been off for about a month and when I fired it up yesterday the static was back. This RFC is a coil about 1" in diameter and a 1/4" thick and is mounted with a screw and nut to the chassis. Looks original and it looks good. Not frayed, broken etc.
::::
::::Momentarily short out the RFC. Does the static go away?
::::
::::::The static is constant and is not affected by the volume or tone control pots. There at min. or max. and everywhere in between.
::::::
::::::Ok, next, is the static there when the volume control is at minimum?
::::::
::::::Gary
::::::
::::::
::::::::Okay did that Gary and the static is still there. Volume also went completely away with that test. Sure appreciate this help. Johnny
::::::::
::::::::Next test:
::::::::
::::::::Re-connect the cathode bypass capacitor then connect a .1 uf capacitor (temporay) from the grid of the 27 to ground. If the static goes away the problem is before the det/audio stage.
::::::::
::::::::Gary
::::::::::Okay. Yes the volume is all but gone as expected and I don't hear the static and I'm not seeing it on the o-scope. The schematic looks like the cap is called out as a .1mfd but could this be wrong? I never powered the radio up when I got it. Just replaced all the caps. This is the second new cap I've tried and it makes no difference. I even replaced the 40K resistor. If I did try a different value on the cap which way should I go? From .1 towards 1 or towards .01? I've checked all associated components that I see the static on with my scope and I'm just not finding anything. I've even swapped out tubes. Let me define this static. It's not static like you might associate with "snow" on a TV set it's more of a "snap-crackle-pop" with no real frequency to it. Does this help?
::::::::::
::::::::::Johnny,
::::::::::
::::::::::Try this simple test:
::::::::::Disconnect one side of the .1 uf (cathode bypass capacitor) and see if the static stops. The audio output should decrease but if the static stops it indicates that the capacitor is breaking down and needs replacing.
::::::::::
::::::::::Gary
::::::::::
::::::::::
::::::::::
:::::::::::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
:::::::::::Some of you good folks have helped with this one before.
:::::::::::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
:::::::::::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
:::::::::::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
:::::::::::

11/5/2008 2:45:33 PMJohnny

:Okay can do. What is that going to tell me?
:
:A few more suggestions:
:
:Disconnect the .001 uf cap on the plate of the 27, static gone?
:
:Disconnect, the .5 uf capacitor on the audio transformer, static gone?
:
:Gary
:
::
:::Yeah I've done all that groovy stuff but I might as well go through it again. I'll let ya know. Thanks Gary!
:::
:::Have you tried tapping tubes, components, and solder joints, or moving wires around etc? This may be a mecahnical problem, wire shorting to the chassis, cold solder joint, dirty tube socket.
:::
:::Gary
:::
:::::When I short the RFC the static goes away for a while then comes back. When I first noticed this problem I found that one of the RFC leads was very close to the chassis and arcing to it. I reworked all that and the static went away. The radio has been off for about a month and when I fired it up yesterday the static was back. This RFC is a coil about 1" in diameter and a 1/4" thick and is mounted with a screw and nut to the chassis. Looks original and it looks good. Not frayed, broken etc.
:::::
:::::Momentarily short out the RFC. Does the static go away?
:::::
:::::::The static is constant and is not affected by the volume or tone control pots. There at min. or max. and everywhere in between.
:::::::
:::::::Ok, next, is the static there when the volume control is at minimum?
:::::::
:::::::Gary
:::::::
:::::::
:::::::::Okay did that Gary and the static is still there. Volume also went completely away with that test. Sure appreciate this help. Johnny
:::::::::
:::::::::Next test:
:::::::::
:::::::::Re-connect the cathode bypass capacitor then connect a .1 uf capacitor (temporay) from the grid of the 27 to ground. If the static goes away the problem is before the det/audio stage.
:::::::::
:::::::::Gary
:::::::::::Okay. Yes the volume is all but gone as expected and I don't hear the static and I'm not seeing it on the o-scope. The schematic looks like the cap is called out as a .1mfd but could this be wrong? I never powered the radio up when I got it. Just replaced all the caps. This is the second new cap I've tried and it makes no difference. I even replaced the 40K resistor. If I did try a different value on the cap which way should I go? From .1 towards 1 or towards .01? I've checked all associated components that I see the static on with my scope and I'm just not finding anything. I've even swapped out tubes. Let me define this static. It's not static like you might associate with "snow" on a TV set it's more of a "snap-crackle-pop" with no real frequency to it. Does this help?
:::::::::::
:::::::::::Johnny,
:::::::::::
:::::::::::Try this simple test:
:::::::::::Disconnect one side of the .1 uf (cathode bypass capacitor) and see if the static stops. The audio output should decrease but if the static stops it indicates that the capacitor is breaking down and needs replacing.
:::::::::::
:::::::::::Gary
:::::::::::
:::::::::::
:::::::::::
::::::::::::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
::::::::::::Some of you good folks have helped with this one before.
::::::::::::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
::::::::::::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
::::::::::::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
::::::::::::

11/5/2008 6:00:49 PMGary W. Prutchick

Intermittent breakdown of either of these capacitors could result is "static".

Gary

::Okay can do. What is that going to tell me?
::
::A few more suggestions:
::
::Disconnect the .001 uf cap on the plate of the 27, static gone?
::
::Disconnect, the .5 uf capacitor on the audio transformer, static gone?
::
::Gary
::
:::
::::Yeah I've done all that groovy stuff but I might as well go through it again. I'll let ya know. Thanks Gary!
::::
::::Have you tried tapping tubes, components, and solder joints, or moving wires around etc? This may be a mecahnical problem, wire shorting to the chassis, cold solder joint, dirty tube socket.
::::
::::Gary
::::
::::::When I short the RFC the static goes away for a while then comes back. When I first noticed this problem I found that one of the RFC leads was very close to the chassis and arcing to it. I reworked all that and the static went away. The radio has been off for about a month and when I fired it up yesterday the static was back. This RFC is a coil about 1" in diameter and a 1/4" thick and is mounted with a screw and nut to the chassis. Looks original and it looks good. Not frayed, broken etc.
::::::
::::::Momentarily short out the RFC. Does the static go away?
::::::
::::::::The static is constant and is not affected by the volume or tone control pots. There at min. or max. and everywhere in between.
::::::::
::::::::Ok, next, is the static there when the volume control is at minimum?
::::::::
::::::::Gary
::::::::
::::::::
::::::::::Okay did that Gary and the static is still there. Volume also went completely away with that test. Sure appreciate this help. Johnny
::::::::::
::::::::::Next test:
::::::::::
::::::::::Re-connect the cathode bypass capacitor then connect a .1 uf capacitor (temporay) from the grid of the 27 to ground. If the static goes away the problem is before the det/audio stage.
::::::::::
::::::::::Gary
::::::::::::Okay. Yes the volume is all but gone as expected and I don't hear the static and I'm not seeing it on the o-scope. The schematic looks like the cap is called out as a .1mfd but could this be wrong? I never powered the radio up when I got it. Just replaced all the caps. This is the second new cap I've tried and it makes no difference. I even replaced the 40K resistor. If I did try a different value on the cap which way should I go? From .1 towards 1 or towards .01? I've checked all associated components that I see the static on with my scope and I'm just not finding anything. I've even swapped out tubes. Let me define this static. It's not static like you might associate with "snow" on a TV set it's more of a "snap-crackle-pop" with no real frequency to it. Does this help?
::::::::::::
::::::::::::Johnny,
::::::::::::
::::::::::::Try this simple test:
::::::::::::Disconnect one side of the .1 uf (cathode bypass capacitor) and see if the static stops. The audio output should decrease but if the static stops it indicates that the capacitor is breaking down and needs replacing.
::::::::::::
::::::::::::Gary
::::::::::::
::::::::::::
::::::::::::
:::::::::::::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
:::::::::::::Some of you good folks have helped with this one before.
:::::::::::::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
:::::::::::::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
:::::::::::::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
:::::::::::::

11/5/2008 7:41:31 PMJohnny

:Well removing the mystery .001 cap didn't fix it and isolating the .001 and .5 didn't do it. I'm stumped right now. I can really see the static being amplified on the plates of the two 47 audio tubes and when I short the RFC to ground momentarilly the static still goes away for a while and then returns after a few minutes. I'll just have to keep looking.
:
:Intermittent breakdown of either of these capacitors could result is "static".
:
:Gary
:
:
:::Okay can do. What is that going to tell me?
:::
:::A few more suggestions:
:::
:::Disconnect the .001 uf cap on the plate of the 27, static gone?
:::
:::Disconnect, the .5 uf capacitor on the audio transformer, static gone?
:::
:::Gary
:::
::::
:::::Yeah I've done all that groovy stuff but I might as well go through it again. I'll let ya know. Thanks Gary!
:::::
:::::Have you tried tapping tubes, components, and solder joints, or moving wires around etc? This may be a mecahnical problem, wire shorting to the chassis, cold solder joint, dirty tube socket.
:::::
:::::Gary
:::::
:::::::When I short the RFC the static goes away for a while then comes back. When I first noticed this problem I found that one of the RFC leads was very close to the chassis and arcing to it. I reworked all that and the static went away. The radio has been off for about a month and when I fired it up yesterday the static was back. This RFC is a coil about 1" in diameter and a 1/4" thick and is mounted with a screw and nut to the chassis. Looks original and it looks good. Not frayed, broken etc.
:::::::
:::::::Momentarily short out the RFC. Does the static go away?
:::::::
:::::::::The static is constant and is not affected by the volume or tone control pots. There at min. or max. and everywhere in between.
:::::::::
:::::::::Ok, next, is the static there when the volume control is at minimum?
:::::::::
:::::::::Gary
:::::::::
:::::::::
:::::::::::Okay did that Gary and the static is still there. Volume also went completely away with that test. Sure appreciate this help. Johnny
:::::::::::
:::::::::::Next test:
:::::::::::
:::::::::::Re-connect the cathode bypass capacitor then connect a .1 uf capacitor (temporay) from the grid of the 27 to ground. If the static goes away the problem is before the det/audio stage.
:::::::::::
:::::::::::Gary
:::::::::::::Okay. Yes the volume is all but gone as expected and I don't hear the static and I'm not seeing it on the o-scope. The schematic looks like the cap is called out as a .1mfd but could this be wrong? I never powered the radio up when I got it. Just replaced all the caps. This is the second new cap I've tried and it makes no difference. I even replaced the 40K resistor. If I did try a different value on the cap which way should I go? From .1 towards 1 or towards .01? I've checked all associated components that I see the static on with my scope and I'm just not finding anything. I've even swapped out tubes. Let me define this static. It's not static like you might associate with "snow" on a TV set it's more of a "snap-crackle-pop" with no real frequency to it. Does this help?
:::::::::::::
:::::::::::::Johnny,
:::::::::::::
:::::::::::::Try this simple test:
:::::::::::::Disconnect one side of the .1 uf (cathode bypass capacitor) and see if the static stops. The audio output should decrease but if the static stops it indicates that the capacitor is breaking down and needs replacing.
:::::::::::::
:::::::::::::Gary
:::::::::::::
:::::::::::::
:::::::::::::
::::::::::::::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
::::::::::::::Some of you good folks have helped with this one before.
::::::::::::::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
::::::::::::::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
::::::::::::::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
::::::::::::::

11/5/2008 8:21:27 PMGary W. Prutchick

Johnny,

There isn't much left!

What happens if you remove the screw from the RFC so it is not touching the chassis?

At what points in the circuit do you observe the noise with your scope, and what are the relative amplitudes?

Can you see the noise on the power supply? Is it possible this noise is coming from a breakdown in a power supply filter?

Gary

::Well removing the mystery .001 cap didn't fix it and isolating the .001 and .5 didn't do it. I'm stumped right now. I can really see the static being amplified on the plates of the two 47 audio tubes and when I short the RFC to ground momentarilly the static still goes away for a while and then returns after a few minutes. I'll just have to keep looking.
::
::Intermittent breakdown of either of these capacitors could result is "static".
::
::Gary
::
::
::::Okay can do. What is that going to tell me?
::::
::::A few more suggestions:
::::
::::Disconnect the .001 uf cap on the plate of the 27, static gone?
::::
::::Disconnect, the .5 uf capacitor on the audio transformer, static gone?
::::
::::Gary
::::
:::::
::::::Yeah I've done all that groovy stuff but I might as well go through it again. I'll let ya know. Thanks Gary!
::::::
::::::Have you tried tapping tubes, components, and solder joints, or moving wires around etc? This may be a mecahnical problem, wire shorting to the chassis, cold solder joint, dirty tube socket.
::::::
::::::Gary
::::::
::::::::When I short the RFC the static goes away for a while then comes back. When I first noticed this problem I found that one of the RFC leads was very close to the chassis and arcing to it. I reworked all that and the static went away. The radio has been off for about a month and when I fired it up yesterday the static was back. This RFC is a coil about 1" in diameter and a 1/4" thick and is mounted with a screw and nut to the chassis. Looks original and it looks good. Not frayed, broken etc.
::::::::
::::::::Momentarily short out the RFC. Does the static go away?
::::::::
::::::::::The static is constant and is not affected by the volume or tone control pots. There at min. or max. and everywhere in between.
::::::::::
::::::::::Ok, next, is the static there when the volume control is at minimum?
::::::::::
::::::::::Gary
::::::::::
::::::::::
::::::::::::Okay did that Gary and the static is still there. Volume also went completely away with that test. Sure appreciate this help. Johnny
::::::::::::
::::::::::::Next test:
::::::::::::
::::::::::::Re-connect the cathode bypass capacitor then connect a .1 uf capacitor (temporay) from the grid of the 27 to ground. If the static goes away the problem is before the det/audio stage.
::::::::::::
::::::::::::Gary
::::::::::::::Okay. Yes the volume is all but gone as expected and I don't hear the static and I'm not seeing it on the o-scope. The schematic looks like the cap is called out as a .1mfd but could this be wrong? I never powered the radio up when I got it. Just replaced all the caps. This is the second new cap I've tried and it makes no difference. I even replaced the 40K resistor. If I did try a different value on the cap which way should I go? From .1 towards 1 or towards .01? I've checked all associated components that I see the static on with my scope and I'm just not finding anything. I've even swapped out tubes. Let me define this static. It's not static like you might associate with "snow" on a TV set it's more of a "snap-crackle-pop" with no real frequency to it. Does this help?
::::::::::::::
::::::::::::::Johnny,
::::::::::::::
::::::::::::::Try this simple test:
::::::::::::::Disconnect one side of the .1 uf (cathode bypass capacitor) and see if the static stops. The audio output should decrease but if the static stops it indicates that the capacitor is breaking down and needs replacing.
::::::::::::::
::::::::::::::Gary
::::::::::::::
::::::::::::::
::::::::::::::
:::::::::::::::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
:::::::::::::::Some of you good folks have helped with this one before.
:::::::::::::::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
:::::::::::::::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
:::::::::::::::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
:::::::::::::::

11/5/2008 9:39:06 PMJohnny

:There sure isn't much left. I have the screw removed now and there's still no change. I really see the static amplified at the plates of the 47 audio tubes. I believe it is at the screen grids of the 47's also but of course at lower amplitudes. Could this be a bad audio transformer? I will isolate it tomorrow and check resistance. I looked at it while in the circuit and I'm seeing 4K across the primaries, 5K across the secondaries and 2.5K each secondary lead to grounded center tap. I didn't pay attention to the actual amplitude but looking back I'm thinking a couple hundred millivolts peak to peak but it is so unstable I really don't think it could actually be measured.
:
:Johnny,
:
:There isn't much left!
:
:What happens if you remove the screw from the RFC so it is not touching the chassis?
:
:At what points in the circuit do you observe the noise with your scope, and what are the relative amplitudes?
:
:Can you see the noise on the power supply? Is it possible this noise is coming from a breakdown in a power supply filter?
:
:Gary
:
:
:::Well removing the mystery .001 cap didn't fix it and isolating the .001 and .5 didn't do it. I'm stumped right now. I can really see the static being amplified on the plates of the two 47 audio tubes and when I short the RFC to ground momentarilly the static still goes away for a while and then returns after a few minutes. I'll just have to keep looking.
:::
:::Intermittent breakdown of either of these capacitors could result is "static".
:::
:::Gary
:::
:::
:::::Okay can do. What is that going to tell me?
:::::
:::::A few more suggestions:
:::::
:::::Disconnect the .001 uf cap on the plate of the 27, static gone?
:::::
:::::Disconnect, the .5 uf capacitor on the audio transformer, static gone?
:::::
:::::Gary
:::::
::::::
:::::::Yeah I've done all that groovy stuff but I might as well go through it again. I'll let ya know. Thanks Gary!
:::::::
:::::::Have you tried tapping tubes, components, and solder joints, or moving wires around etc? This may be a mecahnical problem, wire shorting to the chassis, cold solder joint, dirty tube socket.
:::::::
:::::::Gary
:::::::
:::::::::When I short the RFC the static goes away for a while then comes back. When I first noticed this problem I found that one of the RFC leads was very close to the chassis and arcing to it. I reworked all that and the static went away. The radio has been off for about a month and when I fired it up yesterday the static was back. This RFC is a coil about 1" in diameter and a 1/4" thick and is mounted with a screw and nut to the chassis. Looks original and it looks good. Not frayed, broken etc.
:::::::::
:::::::::Momentarily short out the RFC. Does the static go away?
:::::::::
:::::::::::The static is constant and is not affected by the volume or tone control pots. There at min. or max. and everywhere in between.
:::::::::::
:::::::::::Ok, next, is the static there when the volume control is at minimum?
:::::::::::
:::::::::::Gary
:::::::::::
:::::::::::
:::::::::::::Okay did that Gary and the static is still there. Volume also went completely away with that test. Sure appreciate this help. Johnny
:::::::::::::
:::::::::::::Next test:
:::::::::::::
:::::::::::::Re-connect the cathode bypass capacitor then connect a .1 uf capacitor (temporay) from the grid of the 27 to ground. If the static goes away the problem is before the det/audio stage.
:::::::::::::
:::::::::::::Gary
:::::::::::::::Okay. Yes the volume is all but gone as expected and I don't hear the static and I'm not seeing it on the o-scope. The schematic looks like the cap is called out as a .1mfd but could this be wrong? I never powered the radio up when I got it. Just replaced all the caps. This is the second new cap I've tried and it makes no difference. I even replaced the 40K resistor. If I did try a different value on the cap which way should I go? From .1 towards 1 or towards .01? I've checked all associated components that I see the static on with my scope and I'm just not finding anything. I've even swapped out tubes. Let me define this static. It's not static like you might associate with "snow" on a TV set it's more of a "snap-crackle-pop" with no real frequency to it. Does this help?
:::::::::::::::
:::::::::::::::Johnny,
:::::::::::::::
:::::::::::::::Try this simple test:
:::::::::::::::Disconnect one side of the .1 uf (cathode bypass capacitor) and see if the static stops. The audio output should decrease but if the static stops it indicates that the capacitor is breaking down and needs replacing.
:::::::::::::::
:::::::::::::::Gary
:::::::::::::::
:::::::::::::::
:::::::::::::::
::::::::::::::::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
::::::::::::::::Some of you good folks have helped with this one before.
::::::::::::::::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
::::::::::::::::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
::::::::::::::::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
::::::::::::::::

11/5/2008 10:08:54 AMBill VA

Johnny, I know it's just me but I'm confused on the point in the circuit you are grounding. Is the ground for the 40K and the .1 cap same (chassis ground) as other ground points?

Bill

11/5/2008 10:47:12 AMJohnny

:Come on in Bill. This has been fun. The ground on the .1mfd cap and the 40K resistor are common to each other and go to chassis ground. When the static is present I can momentarilly short the 27 tube side of this parallel rc circuit to ground and the static goes away for a while. Just like what Gary and I are doing now but shorting the RFC instead.
:
:Johnny, I know it's just me but I'm confused on the point in the circuit you are grounding. Is the ground for the 40K and the .1 cap same (chassis ground) as other ground points?
:
:Bill
:
::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
::Some of you good folks have helped with this one before.
::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
::

11/5/2008 11:23:12 AMRadiodoc

Johnny,

If I was a betting person, my bet would be the driver transformer causing the problem (or possibly a solder connection on one of its leads). You may try lifting the primary lead from B+ (the lead that does not go to the RFC) and see if the noise dissapears. Another possibility is the insulation between the RFC winding and the screw mounting it breaking down to chassis/ground.

Radiodoc
*******************

::Come on in Bill. This has been fun. The ground on the .1mfd cap and the 40K resistor are common to each other and go to chassis ground. When the static is present I can momentarilly short the 27 tube side of this parallel rc circuit to ground and the static goes away for a while. Just like what Gary and I are doing now but shorting the RFC instead.
::
::Johnny, I know it's just me but I'm confused on the point in the circuit you are grounding. Is the ground for the 40K and the .1 cap same (chassis ground) as other ground points?
::
::Bill
::
:::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
:::Some of you good folks have helped with this one before.
:::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
:::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
:::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
:::

11/5/2008 11:38:33 AMJohnny

:Thanks doc! I've been through all those steps but I will pull that RFC again and check it. I opened the transformer and it looks real good. Touched all the solder joints anyway. I'm kinda starting from scratch again. There's just no reason why I should have the static but it's there so it must be something I'm not seeing or overlooking.
:
:Johnny,
:
:If I was a betting person, my bet would be the driver transformer causing the problem (or possibly a solder connection on one of its leads). You may try lifting the primary lead from B+ (the lead that does not go to the RFC) and see if the noise dissapears. Another possibility is the insulation between the RFC winding and the screw mounting it breaking down to chassis/ground.
:
:Radiodoc
:*******************
:
:
:::Come on in Bill. This has been fun. The ground on the .1mfd cap and the 40K resistor are common to each other and go to chassis ground. When the static is present I can momentarilly short the 27 tube side of this parallel rc circuit to ground and the static goes away for a while. Just like what Gary and I are doing now but shorting the RFC instead.
:::
:::Johnny, I know it's just me but I'm confused on the point in the circuit you are grounding. Is the ground for the 40K and the .1 cap same (chassis ground) as other ground points?
:::
:::Bill
:::
::::Hello all! I've been a little quiet for a while. Everything from a collapsed lung to tooth extractions.
::::Some of you good folks have helped with this one before.
::::I turned on my Airline 62-9 after it had sat for a month or so and the static problem has returned. All along things have pointed to that "RFC" coil between the 27 tube and the transformer that feeds the two 47 audio tubes. So this morning I tore into it again and while probing around with the o-scope trying to find a possible source for the static the ground collar on the scope probe touched the side of the 40K resistor that is in parallel with the .1mfd cap that is connected to the same 27 tube as the RFC coil. The other side of this R/C circuit goes to ground. A very audible pop was heard from the speakers and immediately the static was gone. The volume even sounds better.
::::So I turned the radio off and let it set for a while. Turned it back on and the static is there but alot less. I intentionally grounded this same spot again that my probe touched and the static goes away.
::::All the components around the RFC coil are new and I have changed out the 27 tube. Only thing that is original is the 40K resistor that is in parallel with the .1mfd cap. This 40K resistor reads good and within tolerance. Could this resistor or even the new .1 cap be bad and causing this static and when I momentarily ground it causes it to go away? Sure appreciate the help!!!. In the meantime I might as well get a 40K resistor and new cap just in case.
::::