Hi, I am baffled at this point. Have a 2a5 output tube that is running blue (gassy).Replaced it with another nos tube and it also runs blue.I get a hammer not motor boating when tunning sometimes.You can see the pulse in the tube.Can't run it for long.Although it does not get worse with time . Cathode to grid -16.25 cathode to screen 250v cathode to plate 270 v .It is an rca 220 .What am I missing ? Most likley would think a short but voltages are normal.Table says grid 16.5 not neg, 16.5 ? Thanks for any help !

:Hi, I am baffled at this point. Have a 2a5 output tube that is running blue (gassy).Replaced it with another nos tube and it also runs blue.I get a hammer not motor boating when tunning sometimes.You can see the pulse in the tube.Can't run it for long.Although it does not get worse with time . Cathode to grid -16.25 cathode to screen 250v cathode to plate 270 v .It is an rca 220 .What am I missing ? Most likley would think a short but voltages are normal.Table says grid 16.5 not neg, 16.5 ? Thanks for any help !

Correction cathode to screen 270 cathode to plate 250

::Hi, I am baffled at this point. Have a 2a5 output tube that is running blue (gassy).Replaced it with another nos tube and it also runs blue.I get a hammer not motor boating when tunning sometimes.You can see the pulse in the tube.Can't run it for long.Although it does not get worse with time . Cathode to grid -16.25 cathode to screen 250v cathode to plate 270 v .It is an rca 220 .What am I missing ? Most likley would think a short but voltages are normal.Table says grid 16.5 not neg, 16.5 ? Thanks for any help !
:
:Correction cathode to screen 270 cathode to plate 250

Hi Bill,
The grid needs to be negative with respect to the cathode, so if you place your digital volt meter negative on the cathode and positive on the grid, the reading needs to be neagative.
From my reading of your posting it seems that is what you have. I got tedious because I wanted to make sure.
If the grid voltage is OK, I would tend to suspect the output transformer, perhaps the wrong kind or shorted primary windings.
It is possible for an NOS tube to be gassy. It is also possible for an overloaded tube to glow blue, too. I have seen it.
How does the rectifier look?

Best Regards,

Bill Grimm

:::Hi, I am baffled at this point. Have a 2a5 output tube that is running blue (gassy).Replaced it with another nos tube and it also runs blue.I get a hammer not motor boating when tunning sometimes.You can see the pulse in the tube.Can't run it for long.Although it does not get worse with time . Cathode to grid -16.25 cathode to screen 250v cathode to plate 270 v .It is an rca 220 .What am I missing ? Most likley would think a short but voltages are normal.Table says grid 16.5 not neg, 16.5 ? Thanks for any help !
::
::Correction cathode to screen 270 cathode to plate 250
:
:Hi Bill,
: The grid needs to be negative with respect to the cathode, so if you place your digital volt meter negative on the cathode and positive on the grid, the reading needs to be neagative.
: From my reading of your posting it seems that is what you have. I got tedious because I wanted to make sure.
: If the grid voltage is OK, I would tend to suspect the output transformer, perhaps the wrong kind or shorted primary windings.
: It is possible for an NOS tube to be gassy. It is also possible for an overloaded tube to glow blue, too. I have seen it.
: How does the rectifier look?
:
:Best Regards,
:
:Bill Grimm

The schematic is hard to read, but you have a capacitor and something else (tone control?) across the output transformer primary. Open a lead of each and see what happens. And, are you saying cathode to screen is higher than to plate? Hmmmm...
Lewis L

::::Hi, I am baffled at this point. Have a 2a5 output tube that is running blue (gassy).Replaced it with another nos tube and it also runs blue.I get a hammer not motor boating when tunning sometimes.You can see the pulse in the tube.Can't run it for long.Although it does not get worse with time . Cathode to grid -16.25 cathode to screen 250v cathode to plate 270 v .It is an rca 220 .What am I missing ? Most likley would think a short but voltages are normal.Table says grid 16.5 not neg, 16.5 ? Thanks for any help !
:::
:::Correction cathode to screen 270 cathode to plate 250
::
::Hi Bill,
:: The grid needs to be negative with respect to the cathode, so if you place your digital volt meter negative on the cathode and positive on the grid, the reading needs to be neagative.
:: From my reading of your posting it seems that is what you have. I got tedious because I wanted to make sure.
:: If the grid voltage is OK, I would tend to suspect the output transformer, perhaps the wrong kind or shorted primary windings.
:: It is possible for an NOS tube to be gassy. It is also possible for an overloaded tube to glow blue, too. I have seen it.
:: How does the rectifier look?
::
::Best Regards,
::
::Bill Grimm
:
:The schematic is hard to read, but you have a capacitor and something else (tone control?) across the output transformer primary. Open a lead of each and see what happens. And, are you saying cathode to screen is higher than to plate? Hmmmm...
:Lewis L

Bill and Lewis , Thanks for the input . All suggestion make sense , clears my mental block .Bias voltages are correct and to the print .Screen is higher than plate by about ten volts or so .Not sure why in theory but it is ok.I like the idea of taking the cap and (cap+ tone control off) to see what happens .Maybe I put a wrong value cap in( eye sight being a factor).So I have some things to try now .Unfortunatley I was banking on bad tube so I put it all back together.Then obtianed second tube In a couple days I'll get it out and go over it again. I think there is some kind of short.Not sure how I can tell if it is a wrong output transfomer but that also is very possible .I checked it to ground and all looks ok.The resistance was about 400 ohms on the primary. There is no info on the print itself.If it is the wrong transformer that will be hardest to figure. Hope I screwed up a cap.You have me thinking a wrong value could be a short at AF. Rectifier is perfect no blue, voltage little higher than spec as expected .Other odd symptoms , seems to play normal at high volume .Hammers at low volume Does not seem to be affected by tone control.It should be so that is not working normal.Oscillator detector also slightly blue and pulses with this output tube. Thanks for the help!I feel like a got a chance at it. Will let you how I make out after I get it back on the bench and check this stuff !

Hi Bill

The tube may not be gassy? A gassy tube will have a purple color within elements. A blue glow just inside the glass is caused by electrons striking the glass. This glow may follow sound of the radio.

Don't think your tube which has - 16.25 volts bias is gassy. If gassy this voltage usually drops.

Norm

:::::Hi, I am baffled at this point. Have a 2a5 output tube that is running blue (gassy).Replaced it with another nos tube and it also runs blue.I get a hammer not motor boating when tunning sometimes.You can see the pulse in the tube.Can't run it for long.Although it does not get worse with time . Cathode to grid -16.25 cathode to screen 250v cathode to plate 270 v .It is an rca 220 .What am I missing ? Most likley would think a short but voltages are normal.Table says grid 16.5 not neg, 16.5 ? Thanks for any help !
::::
::::Correction cathode to screen 270 cathode to plate 250
:::
:::Hi Bill,
::: The grid needs to be negative with respect to the cathode, so if you place your digital volt meter negative on the cathode and positive on the grid, the reading needs to be neagative.
::: From my reading of your posting it seems that is what you have. I got tedious because I wanted to make sure.
::: If the grid voltage is OK, I would tend to suspect the output transformer, perhaps the wrong kind or shorted primary windings.
::: It is possible for an NOS tube to be gassy. It is also possible for an overloaded tube to glow blue, too. I have seen it.
::: How does the rectifier look?
:::
:::Best Regards,
:::
:::Bill Grimm
::
::The schematic is hard to read, but you have a capacitor and something else (tone control?) across the output transformer primary. Open a lead of each and see what happens. And, are you saying cathode to screen is higher than to plate? Hmmmm...
::Lewis L
:
:Bill and Lewis , Thanks for the input . All suggestion make sense , clears my mental block .Bias voltages are correct and to the print .Screen is higher than plate by about ten volts or so .Not sure why in theory but it is ok.I like the idea of taking the cap and (cap+ tone control off) to see what happens .Maybe I put a wrong value cap in( eye sight being a factor).So I have some things to try now .Unfortunatley I was banking on bad tube so I put it all back together.Then obtianed second tube In a couple days I'll get it out and go over it again. I think there is some kind of short.Not sure how I can tell if it is a wrong output transfomer but that also is very possible .I checked it to ground and all looks ok.The resistance was about 400 ohms on the primary. There is no info on the print itself.If it is the wrong transformer that will be hardest to figure. Hope I screwed up a cap.You have me thinking a wrong value could be a short at AF. Rectifier is perfect no blue, voltage little higher than spec as expected .Other odd symptoms , seems to play normal at high volume .Hammers at low volume Does not seem to be affected by tone control.It should be so that is not working normal.Oscillator detector also slightly blue and pulses with this output tube. Thanks for the help!I feel like a got a chance at it. Will let you how I make out after I get it back on the bench and check this stuff !

Norm , After checking what the other guys suggested below I find nothing wrong .I assumed there was a short now I not sure what to think .It is blue as opposed to purple .I've seen that on a shorted rectifer when plates got hot enough.So this is different . And it pulses with the tunning like you said .Just makes a thumping noise as it does it which can't be good and I've never experienced.Experience being one thing I don't have a lot of here!But it does settle out if I adjust the volume-tunning and operate pretty decent.Anyway this is what I have found from checks.
Disconnect cap ahead of output transformer - made symtom worse.
Disconnect tone control - made symtom worse.
disconnect both of above - same result.
Found spec on print for transformer 400 ohm -actual 457ohms
Put 327ohm (what I had ) in series with plate 10vdc
or so about 30 ma . Not sure if that is a correct test but was curious . Seems to be right on the curves for tube.All voltages for bias normal .
This means no short to me ,correct ?
Do I just except it as is? I am ok with it if this sounds normal for a 1934 set.Norm when it does this the bias voltages do upset.Otherwise they are steady.
Does a gassy tube have a constant loss of bias? Thanks for all help from all and suggestions from all of you! I am wondering what to do next if anything ?

:Hi Bill
:
: The tube may not be gassy? A gassy tube will have a purple color within elements. A blue glow just inside the glass is caused by electrons striking the glass. This glow may follow sound of the radio.
:
: Don't think your tube which has - 16.25 volts bias is gassy. If gassy this voltage usually drops.
:
:Norm
:
::::::Hi, I am baffled at this point. Have a 2a5 output tube that is running blue (gassy).Replaced it with another nos tube and it also runs blue.I get a hammer not motor boating when tunning sometimes.You can see the pulse in the tube.Can't run it for long.Although it does not get worse with time . Cathode to grid -16.25 cathode to screen 250v cathode to plate 270 v .It is an rca 220 .What am I missing ? Most likley would think a short but voltages are normal.Table says grid 16.5 not neg, 16.5 ? Thanks for any help !
:::::
:::::Correction cathode to screen 270 cathode to plate 250
::::
::::Hi Bill,
:::: The grid needs to be negative with respect to the cathode, so if you place your digital volt meter negative on the cathode and positive on the grid, the reading needs to be neagative.
:::: From my reading of your posting it seems that is what you have. I got tedious because I wanted to make sure.
:::: If the grid voltage is OK, I would tend to suspect the output transformer, perhaps the wrong kind or shorted primary windings.
:::: It is possible for an NOS tube to be gassy. It is also possible for an overloaded tube to glow blue, too. I have seen it.
:::: How does the rectifier look?
::::
::::Best Regards,
::::
::::Bill Grimm
:::
:::The schematic is hard to read, but you have a capacitor and something else (tone control?) across the output transformer primary. Open a lead of each and see what happens. And, are you saying cathode to screen is higher than to plate? Hmmmm...
:::Lewis L
::
::Bill and Lewis , Thanks for the input . All suggestion make sense , clears my mental block .Bias voltages are correct and to the print .Screen is higher than plate by about ten volts or so .Not sure why in theory but it is ok.I like the idea of taking the cap and (cap+ tone control off) to see what happens .Maybe I put a wrong value cap in( eye sight being a factor).So I have some things to try now .Unfortunatley I was banking on bad tube so I put it all back together.Then obtianed second tube In a couple days I'll get it out and go over it again. I think there is some kind of short.Not sure how I can tell if it is a wrong output transfomer but that also is very possible .I checked it to ground and all looks ok.The resistance was about 400 ohms on the primary. There is no info on the print itself.If it is the wrong transformer that will be hardest to figure. Hope I screwed up a cap.You have me thinking a wrong value could be a short at AF. Rectifier is perfect no blue, voltage little higher than spec as expected .Other odd symptoms , seems to play normal at high volume .Hammers at low volume Does not seem to be affected by tone control.It should be so that is not working normal.Oscillator detector also slightly blue and pulses with this output tube. Thanks for the help!I feel like a got a chance at it. Will let you how I make out after I get it back on the bench and check this stuff !

From the term "thumping noise" it sounds like what is called motor boating or low frequency oscillation. This can be caused by several things. You may have an open bypass capacitor a tube shield may be missing. Check wire routing. Are any tube grid wires running too close to tube plate wires. What is the make and model number. I can check one of my books and see if there were any circuit changes or case history failures. Hope this helps

MRO

Hi Bill,
You indeed have a puzzler here.

Since you do not have the model number, tell us the numbers of some of the other tubes in your set. You indicated that some of them had the blue condtion, too.
Filament voltage snould be around 2 volts AC. I am starting to suspect that your set may have had some inappropriate tube substitutions during its lifetime.
I had a Wards Airline that used a 2A5. It never did anything like this.

Best Regards,

Bill Grimm

:Hi Bill,
: You indeed have a puzzler here.
:
: Since you do not have the model number, tell us the numbers of some of the other tubes in your set. You indicated that some of them had the blue condtion, too.
: Filament voltage snould be around 2 volts AC. I am starting to suspect that your set may have had some inappropriate tube substitutions during its lifetime.
: I had a Wards Airline that used a 2A5. It never did anything like this.
:
:Best Regards,
:
:Bill Grimm
:
__________________________

What is the model and make of the set? I think Pentodes will oscilate if the 2nd, and/or 3rd grids don't have the right voltages. Jeremy

mark is on the money. follow his advice. not much to an amplifier. therefore it can't be too much of a puzzler. just look at all of what you should be looking at and you will find the trouble. you shouldn't overlook anything.

norm is also right. blue is normal. purple is typically gas. most heavily driven output tubes glow blue, and some other tubes may glow blue faintly. about the only one that usually won't is the 1st audio. it handles a miniscual current. it probably won't glow purple when it gets gassy, either.

:mark is on the money. follow his advice. not much to an amplifier. therefore it can't be too much of a puzzler. just look at all of what you should be looking at and you will find the trouble. you shouldn't overlook anything.
:
:norm is also right. blue is normal. purple is typically gas. most heavily driven output tubes glow blue, and some other tubes may glow blue faintly. about the only one that usually won't is the 1st audio. it handles a miniscual current. it probably won't glow purple when it gets gassy, either.

All,

Thanks for all the leads . I need to regroup when I have a chunk of time and go at it again.
I beat the heck out of the output tube area. Everything appears to be in spec and normal .I like Norm's thoughts there . I thought short .But the current from the tube at 32 ma kills that line of thought. If it is a voltage or winding momentarily breaking over to ground it will find itself. The output transformer megs out off the scale to ground. Of course a couple hundred volts could change things. I am seeing normal operation most of the time.
The radio is a General Electric Kc-66-MR which boils down to a RCA 220 chassis .That print looks to be right on. The tubes are correct to the print and I have substituted all but the 58's with no change to the issue. I need to put in the new 2A7 at night and see if it glows faintly blue also .
As far a motor boating goes doesn't that come out of the speaker? I am really not coming from a radio back ground so I honestly do not know. But either way to clarify, this thumping comes from the output tube itself. I can start this by turning down the volume. Turn up the volume and it goes away. With the volume up tunning does not start the thumping. So the main trigger of this is low volume.That is my latest observation as I adjust . I am going to check out that area better. Could simply be a bad control on the low end .That would upset things especially with AVC. Should I disconnect that for a bit ? And I will check wire routing. I sleeved 90% of this set so I think that will be ok , but I will double check. In short I think am looking in the wrong section(2a5). If all this fails I am going to get out the Scope and VTVM and divide and conquer. Thanks again for all the input !!!

Bill

::mark is on the money. follow his advice. not much to an amplifier. therefore it can't be too much of a puzzler. just look at all of what you should be looking at and you will find the trouble. you shouldn't overlook anything.
::
::norm is also right. blue is normal. purple is typically gas. most heavily driven output tubes glow blue, and some other tubes may glow blue faintly. about the only one that usually won't is the 1st audio. it handles a miniscual current. it probably won't glow purple when it gets gassy, either.
:
:
:
:All,
:
:Thanks for all the leads . I need to regroup when I have a chunk of time and go at it again.
:I beat the heck out of the output tube area. Everything appears to be in spec and normal .I like Norm's thoughts there . I thought short .But the current from the tube at 32 ma kills that line of thought. If it is a voltage or winding momentarily breaking over to ground it will find itself. The output transformer megs out off the scale to ground. Of course a couple hundred volts could change things. I am seeing normal operation most of the time.
: The radio is a General Electric Kc-66-MR which boils down to a RCA 220 chassis .That print looks to be right on. The tubes are correct to the print and I have substituted all but the 58's with no change to the issue. I need to put in the new 2A7 at night and see if it glows faintly blue also .
:As far a motor boating goes doesn't that come out of the speaker? I am really not coming from a radio back ground so I honestly do not know. But either way to clarify, this thumping comes from the output tube itself. I can start this by turning down the volume. Turn up the volume and it goes away. With the volume up tunning does not start the thumping. So the main trigger of this is low volume.That is my latest observation as I adjust . I am going to check out that area better. Could simply be a bad control on the low end .That would upset things especially with AVC. Should I disconnect that for a bit ? And I will check wire routing. I sleeved 90% of this set so I think that will be ok , but I will double check. In short I think am looking in the wrong section(2a5). If all this fails I am going to get out the Scope and VTVM and divide and conquer. Thanks again for all the input !!!
:
:Bill

Guys,

There is a one-page reprint "THREE REASONS FOR BLUE GLOW" (Sylvania News, Vol. 5 No. 11 (1934) in the February issue of the Tube Collectors Association's the Tube Collector about the blue glow in tubes.

Radiodoc

if the motorboating only occurs when the volume is turned up, then it isn't coming from the output tube. the volume control comes prior to the output tube, so logically the output tube has nothing to do with the motorboating other than that it is part of the chain of items which the motorboating comes from. it is no more guilty than any other item in the chain. if it is well known that the speaker wire is not running anywhere near the 1st audio tube, then one must look for other tubes in the RF section that the speaker wire may be running near. if it isn't running near any of them, make sure that they have proper shielding around the tubes themselves, possibly the grid wires, and possibly the plate wires. establishing shielding around these wires can help if a solution cannot otherwise be found. make sure that all filtering and stabilizing capacitors are in good order, and are of proper value. capacitors on screen grids are important. capacitors in the main power supply are also important. if these capacitors cannot hold the power supply at a stable voltage, fluctuations in load in one circuit will sneak through the power supply and will be imposed upon another circuit. this other circuit will fluctuate, and will return the favor. an oscillation will have been set up, and you will hear it in the speaker.

:if the motorboating only occurs when the volume is turned up, then it isn't coming from the output tube. the volume control comes prior to the output tube, so logically the output tube has nothing to do with the motorboating other than that it is part of the chain of items which the motorboating comes from. it is no more guilty than any other item in the chain. if it is well known that the speaker wire is not running anywhere near the 1st audio tube, then one must look for other tubes in the RF section that the speaker wire may be running near. if it isn't running near any of them, make sure that they have proper shielding around the tubes themselves, possibly the grid wires, and possibly the plate wires. establishing shielding around these wires can help if a solution cannot otherwise be found. make sure that all filtering and stabilizing capacitors are in good order, and are of proper value. capacitors on screen grids are important. capacitors in the main power supply are also important. if these capacitors cannot hold the power supply at a stable voltage, fluctuations in load in one circuit will sneak through the power supply and will be imposed upon another circuit. this other circuit will fluctuate, and will return the favor. an oscillation will have been set up, and you will hear it in the speaker.

Superspark , Thanks for the advise! There are alot of shielded cables in this unit .I am still not sure that what I have is technically motorboating.It could be.
But like motor boating it is working its way through the sections. However it is not audio frequence or it would come out of the speaker.What it apppears to be is a miswired anntena section .Still have not figured it out but think I have made progress.Not much time with work and all .There should be 2 meg between the tap on the volume control and the anntena secondary.Was not wired like that .Practically straight to ground so when volume got turned down that would set things in motion. Like I said wish it had time to disscuss and work on but need couple days to do other things.I think I might have found the source of the issue. If I disconnect noise does not occur .If I put it where I think it should go,one station or no anntena.I think I am about to discover someone elses repair job!Need some clear time to retrace the wiring and check stuff . Thanks for the info ! If I actual get it will post here .By the way tube stays blue but that is ok !

::if the motorboating only occurs when the volume is turned up, then it isn't coming from the output tube. the volume control comes prior to the output tube, so logically the output tube has nothing to do with the motorboating other than that it is part of the chain of items which the motorboating comes from. it is no more guilty than any other item in the chain. if it is well known that the speaker wire is not running anywhere near the 1st audio tube, then one must look for other tubes in the RF section that the speaker wire may be running near. if it isn't running near any of them, make sure that they have proper shielding around the tubes themselves, possibly the grid wires, and possibly the plate wires. establishing shielding around these wires can help if a solution cannot otherwise be found. make sure that all filtering and stabilizing capacitors are in good order, and are of proper value. capacitors on screen grids are important. capacitors in the main power supply are also important. if these capacitors cannot hold the power supply at a stable voltage, fluctuations in load in one circuit will sneak through the power supply and will be imposed upon another circuit. this other circuit will fluctuate, and will return the favor. an oscillation will have been set up, and you will hear it in the speaker.
:
:Superspark , Thanks for the advise! There are alot of shielded cables in this unit .I am still not sure that what I have is technically motorboating.It could be.
:But like motor boating it is working its way through the sections. However it is not audio frequence or it would come out of the speaker.What it apppears to be is a miswired anntena section .Still have not figured it out but think I have made progress.Not much time with work and all .There should be 2 meg between the tap on the volume control and the anntena secondary.Was not wired like that .Practically straight to ground so when volume got turned down that would set things in motion. Like I said wish it had time to disscuss and work on but need couple days to do other things.I think I might have found the source of the issue. If I disconnect noise does not occur .If I put it where I think it should go,one station or no anntena.I think I am about to discover someone elses repair job!Need some clear time to retrace the wiring and check stuff . Thanks for the info ! If I actual get it will post here .By the way tube stays blue but that is ok !

ALL, Thanks for all the good help here !!! It seems that the problem was not that the tube was blue .It was'nt the output tube It seems to have been that 2 meg resistor on the anntena or RF section. I should have picked this up in my voltage checks but did not .
Of course it was not so out of wack when the volume was up.This must have changed the bias enough to start this thing oscillating.Taking 2 meg out of a circiut is a big deal.Not sure how it worked to begin with but at higher volume it did.I think this was an attempt to put a loop anntena on this instead of a long wire by a previous owner.So I was missing whatever was hooked up then.Now it actual works with a long wire.Thanks again for all the advice and help .I would not have found this on the output side !

Bill

:::if the motorboating only occurs when the volume is turned up, then it isn't coming from the output tube. the volume control comes prior to the output tube, so logically the output tube has nothing to do with the motorboating other than that it is part of the chain of items which the motorboating comes from. it is no more guilty than any other item in the chain. if it is well known that the speaker wire is not running anywhere near the 1st audio tube, then one must look for other tubes in the RF section that the speaker wire may be running near. if it isn't running near any of them, make sure that they have proper shielding around the tubes themselves, possibly the grid wires, and possibly the plate wires. establishing shielding around these wires can help if a solution cannot otherwise be found. make sure that all filtering and stabilizing capacitors are in good order, and are of proper value. capacitors on screen grids are important. capacitors in the main power supply are also important. if these capacitors cannot hold the power supply at a stable voltage, fluctuations in load in one circuit will sneak through the power supply and will be imposed upon another circuit. this other circuit will fluctuate, and will return the favor. an oscillation will have been set up, and you will hear it in the speaker.
::
::Superspark , Thanks for the advise! There are alot of shielded cables in this unit .I am still not sure that what I have is technically motorboating.It could be.
::But like motor boating it is working its way through the sections. However it is not audio frequence or it would come out of the speaker.What it apppears to be is a miswired anntena section .Still have not figured it out but think I have made progress.Not much time with work and all .There should be 2 meg between the tap on the volume control and the anntena secondary.Was not wired like that .Practically straight to ground so when volume got turned down that would set things in motion. Like I said wish it had time to disscuss and work on but need couple days to do other things.I think I might have found the source of the issue. If I disconnect noise does not occur .If I put it where I think it should go,one station or no anntena.I think I am about to discover someone elses repair job!Need some clear time to retrace the wiring and check stuff . Thanks for the info ! If I actual get it will post here .By the way tube stays blue but that is ok !
:
:
:ALL, Thanks for all the good help here !!! It seems that the problem was not that the tube was blue .It was'nt the output tube It seems to have been that 2 meg resistor on the anntena or RF section. I should have picked this up in my voltage checks but did not .
:Of course it was not so out of wack when the volume was up.This must have changed the bias enough to start this thing oscillating.Taking 2 meg out of a circiut is a big deal.Not sure how it worked to begin with but at higher volume it did.I think this was an attempt to put a loop anntena on this instead of a long wire by a previous owner.So I was missing whatever was hooked up then.Now it actual works with a long wire.Thanks again for all the advice and help .I would not have found this on the output side !
:
:Bill
:
Hi Bill,
Thanks for the update! It feels good when you have finally gotten it, dosen't it?

Best Regards,

Bill Grimm

::::if the motorboating only occurs when the volume is turned up, then it isn't coming from the output tube. the volume control comes prior to the output tube, so logically the output tube has nothing to do with the motorboating other than that it is part of the chain of items which the motorboating comes from. it is no more guilty than any other item in the chain. if it is well known that the speaker wire is not running anywhere near the 1st audio tube, then one must look for other tubes in the RF section that the speaker wire may be running near. if it isn't running near any of them, make sure that they have proper shielding around the tubes themselves, possibly the grid wires, and possibly the plate wires. establishing shielding around these wires can help if a solution cannot otherwise be found. make sure that all filtering and stabilizing capacitors are in good order, and are of proper value. capacitors on screen grids are important. capacitors in the main power supply are also important. if these capacitors cannot hold the power supply at a stable voltage, fluctuations in load in one circuit will sneak through the power supply and will be imposed upon another circuit. this other circuit will fluctuate, and will return the favor. an oscillation will have been set up, and you will hear it in the speaker.
:::
:::Superspark , Thanks for the advise! There are alot of shielded cables in this unit .I am still not sure that what I have is technically motorboating.It could be.
:::But like motor boating it is working its way through the sections. However it is not audio frequence or it would come out of the speaker.What it apppears to be is a miswired anntena section .Still have not figured it out but think I have made progress.Not much time with work and all .There should be 2 meg between the tap on the volume control and the anntena secondary.Was not wired like that .Practically straight to ground so when volume got turned down that would set things in motion. Like I said wish it had time to disscuss and work on but need couple days to do other things.I think I might have found the source of the issue. If I disconnect noise does not occur .If I put it where I think it should go,one station or no anntena.I think I am about to discover someone elses repair job!Need some clear time to retrace the wiring and check stuff . Thanks for the info ! If I actual get it will post here .By the way tube stays blue but that is ok !
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::ALL, Thanks for all the good help here !!! It seems that the problem was not that the tube was blue .It was'nt the output tube It seems to have been that 2 meg resistor on the anntena or RF section. I should have picked this up in my voltage checks but did not .
::Of course it was not so out of wack when the volume was up.This must have changed the bias enough to start this thing oscillating.Taking 2 meg out of a circiut is a big deal.Not sure how it worked to begin with but at higher volume it did.I think this was an attempt to put a loop anntena on this instead of a long wire by a previous owner.So I was missing whatever was hooked up then.Now it actual works with a long wire.Thanks again for all the advice and help .I would not have found this on the output side !
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::Bill
::
:Hi Bill,
: Thanks for the update! It feels good when you have finally gotten it, dosen't it?
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:Best Regards,
:
:Bill Grimm

Bill , Oh yea ! This was a long haul for me.I usually do not run into this type of stuff.Mostly have done Philco consoles .I have all I can fit in my house now. Have to leave room for wife and kids ! But your right .It's a thrill to bring something back from 1934, and hear it play for the first time in decades .
I work on computers and industrial electronic all day.
But there is no history in that , not the same .These old radio's are a thrill to revive!I can't believe that radios were this good in 1934 ! Sounds great. Thanks agian for all the help , keep fixing stuff !!!
Bill