47 problems (the tube that is!)

3/4/2011 9:33:43 AMSteve Bento

I have 2 47 tubes in a push - pull configuration. (RCA R-20) I finished replacing the caps and the out of tolerace resistors. I also had to replace the input transformer to said P-P amplifier. When I turned the lights off and looked at the tubes I noticed a cobalt blue haze in one of my 47 tubes. I've heard about gaseous tubes but don't know too much about it. I had checked the voltages of both tubes and they both check in normal params. I tested both tubes on my Heathkit TC-2 and both came out 90+ in strength. The radio plays great and very very strong. I also switched around the tubes to see if the other 47 would exibit the same thing, thinking maybe it was just an overvoltage at that tube location. But switching them around did nothing. The tube was still gaseous and the other good 47 stayed good. So my question (I know it's long winded!) is this something I should worry about? Or maybe it's normal? I know some tubes have mercury vapors so maybe that's what this is... Thanks

3/4/2011 9:57:30 AMLewis L

:I have 2 47 tubes in a push - pull configuration. (RCA R-20) I finished replacing the caps and the out of tolerace resistors. I also had to replace the input transformer to said P-P amplifier. When I turned the lights off and looked at the tubes I noticed a cobalt blue haze in one of my 47 tubes. I've heard about gaseous tubes but don't know too much about it. I had checked the voltages of both tubes and they both check in normal params. I tested both tubes on my Heathkit TC-2 and both came out 90+ in strength. The radio plays great and very very strong. I also switched around the tubes to see if the other 47 would exibit the same thing, thinking maybe it was just an overvoltage at that tube location. But switching them around did nothing. The tube was still gaseous and the other good 47 stayed good. So my question (I know it's long winded!) is this something I should worry about? Or maybe it's normal? I know some tubes have mercury vapors so maybe that's what this is... Thanks
:

If the tubes test good and don't show any shorts on the tester, and the Voltages look OK in the radio, I wouldn't worry about a little blue glow. You might touch the power transformer a few times to ensure it is not running too hot.
Lewis

3/4/2011 10:01:04 AMLewis L

::I have 2 47 tubes in a push - pull configuration. (RCA R-20) I finished replacing the caps and the out of tolerace resistors. I also had to replace the input transformer to said P-P amplifier. When I turned the lights off and looked at the tubes I noticed a cobalt blue haze in one of my 47 tubes. I've heard about gaseous tubes but don't know too much about it. I had checked the voltages of both tubes and they both check in normal params. I tested both tubes on my Heathkit TC-2 and both came out 90+ in strength. The radio plays great and very very strong. I also switched around the tubes to see if the other 47 would exibit the same thing, thinking maybe it was just an overvoltage at that tube location. But switching them around did nothing. The tube was still gaseous and the other good 47 stayed good. So my question (I know it's long winded!) is this something I should worry about? Or maybe it's normal? I know some tubes have mercury vapors so maybe that's what this is... Thanks
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:If the tubes test good and don't show any shorts on the tester, and the Voltages look OK in the radio, I wouldn't worry about a little blue glow. You might touch the power transformer a few times to ensure it is not running too hot.
:Lewis

P. S. If it is battery operated. I am assuming there is a battery eliminator used?

3/4/2011 10:13:06 AMSteve Bento

Nope, no batteries, this is a regular AC transformer radio. Thanks, I'll check for heat the next time I turn it on.

3/4/2011 10:25:56 AMSteve Bento

I forgot to mention also that the radio is only pulling less than an amp. It's rated at 145W but I only measured 120W which I guess is good. I have a 1.5A fuse in line also. If that tube was bad wouldn't it start drawing more current? It got me thinking when you mentioned the heated transformer.

3/4/2011 11:02:21 AMNorm Leal

Steve

You mention Blue rather trhan a purple color. If the blue is seen just inside the glass not a problem. If there is a purple color within elements a tube is gassy.

A gassy tube can get worse over time. It can run away drawing current.

Norm

:I forgot to mention also that the radio is only pulling less than an amp. It's rated at 145W but I only measured 120W which I guess is good. I have a 1.5A fuse in line also. If that tube was bad wouldn't it start drawing more current? It got me thinking when you mentioned the heated transformer.
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3/4/2011 12:23:13 PMSteve Bento

Thanks for the response Norm. It's definitely Blue. It looks like a cloud on the inside of the tube. Pretty cool looking actually!
I'll keep an eye on it though, thanks...

:Steve
:
: You mention Blue rather trhan a purple color. If the blue is seen just inside the glass not a problem. If there is a purple color within elements a tube is gassy.
:
: A gassy tube can get worse over time. It can run away drawing current.
:
:Norm
:
::I forgot to mention also that the radio is only pulling less than an amp. It's rated at 145W but I only measured 120W which I guess is good. I have a 1.5A fuse in line also. If that tube was bad wouldn't it start drawing more current? It got me thinking when you mentioned the heated transformer.
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3/4/2011 4:35:58 PMLewis L

:Thanks for the response Norm. It's definitely Blue. It looks like a cloud on the inside of the tube. Pretty cool looking actually!
:I'll keep an eye on it though, thanks...

the radio stations where I worked in my early days had mercury vapor rectifiers. The 5kW guys had six 8008s that flashed merrily with the modulation. Fun to watch.
Lewis

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::Steve
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:: You mention Blue rather trhan a purple color. If the blue is seen just inside the glass not a problem. If there is a purple color within elements a tube is gassy.
::
:: A gassy tube can get worse over time. It can run away drawing current.
::
::Norm
::
:::I forgot to mention also that the radio is only pulling less than an amp. It's rated at 145W but I only measured 120W which I guess is good. I have a 1.5A fuse in line also. If that tube was bad wouldn't it start drawing more current? It got me thinking when you mentioned the heated transformer.
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3/4/2011 4:36:01 PMLewis L

:Thanks for the response Norm. It's definitely Blue. It looks like a cloud on the inside of the tube. Pretty cool looking actually!
:I'll keep an eye on it though, thanks...

the radio stations where I worked in my early days had mercury vapor rectifiers. The 5kW guys had six 8008s that flashed merrily with the modulation. Fun to watch.
Lewis

3/7/2011 12:57:56 AMThomas Dermody

If the glow is on the glass or on the mica, or even on the metal elements (most likely plate, possibly on the inside, with a shadow of the grids present), this is normal cathode ray glow. Some have said that it's a reaction to impurities in the glass, etc., but since I have also seen it on mica and on the elements themselves, that leads me to believe that it is not due to the glass alone. This type of glow is no cause for concern.

If the glow is a purple haze in the tube (usually purple, but sometimes other colors), then this is gas. Gassy tubes can function well, but can run away with current.

3/7/2011 10:06:56 AMSteve Bento

Thanks Thomas, I've heard that it had something to do with the mercury in some tube types. The 2 47 tubes I have are from 2 different manufacturers. THe one I'm talking about could have been made with different materials and hence the difference. The cloud of blue is not specifically located around and one part, it's a vaporous cloud which surrounds the whole center section of the tube. It's good to hear it's not of concern though, they're expensive tubes!

:If the glow is on the glass or on the mica, or even on the metal elements (most likely plate, possibly on the inside, with a shadow of the grids present), this is normal cathode ray glow. Some have said that it's a reaction to impurities in the glass, etc., but since I have also seen it on mica and on the elements themselves, that leads me to believe that it is not due to the glass alone. This type of glow is no cause for concern.
:
:If the glow is a purple haze in the tube (usually purple, but sometimes other colors), then this is gas. Gassy tubes can function well, but can run away with current.
:

3/7/2011 4:20:43 PMBill G.

Hi Steve,
I have some type 83 rectifiers. They are murcury vapor. When on these glow blue. When off one can see little globs of murcury inside.
I also have here a type 80. It glows blue and it is bad. I can see the little crack in the envelope.
Type 47 is not murcury of course. I have taken blue to be a bad sign in a tube, except power output tubes like your 47. So I am in agreement with Sir Thomas here. Don't worry about it and enjoy the glow.

All the Best,

Bill

3/7/2011 10:48:28 PMThomas Dermody

If the glow is a blue fog within the elements, this is a sign of slight gas. You can probably continue to use this tube, but should monitor current draw, and suspect it if distortion occurs, or a cathode resistor overheats.

I have a couple of G45 tubes in use in my Majestic 181 that exhibit this glow. It is definitely a faint fog, and is from gas. It came when I baked the tubes in the oven to increase their emission. The emission may have in fact increased due to this gas release. However, it is slight, and the increased emission is semi-permanent, and the tubes play well, so I just keep using them.

A deeper blue glow that is definitely on the surface of parts within the tube or the glass is, however, not caused by gas, and is of no concern.

3/8/2011 6:17:29 AMcodefox

All tubes are time bombs. If you have a gassy tube which hasn't been fired up in decades, it may heal itself after a couple of days of continuous usage under load, but will probably not last all that much longer. If you have a really nice radio that you want to listen to and keep, replace the tube, they're cheap enough.

3/8/2011 9:58:36 AMSteve Bento

Where do you get your tubes from that they're cheap. I wanna shop there!

:All tubes are time bombs. If you have a gassy tube which hasn't been fired up in decades, it may heal itself after a couple of days of continuous usage under load, but will probably not last all that much longer. If you have a really nice radio that you want to listen to and keep, replace the tube, they're cheap enough.
:
::I forgot to mention also that the radio is only pulling less than an amp. It's rated at 145W but I only measured 120W which I guess is good. I have a 1.5A fuse in line also. If that tube was bad wouldn't it start drawing more current? It got me thinking when you mentioned the heated transformer.
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3/8/2011 11:10:38 AMJohn

:Where do you get your tubes from that they're cheap. I wanna shop there!
:
::All tubes are time bombs. If you have a gassy tube which hasn't been fired up in decades, it may heal itself after a couple of days of continuous usage under load, but will probably not last all that much longer. If you have a really nice radio that you want to listen to and keep, replace the tube, they're cheap enough.
::
:::I forgot to mention also that the radio is only pulling less than an amp. It's rated at 145W but I only measured 120W which I guess is good. I have a 1.5A fuse in line also. If that tube was bad wouldn't it start drawing more current? It got me thinking when you mentioned the heated transformer.
:::
Source of relative inexpensive tubes: findatube.com
#47 tubes for $12 Nos, $7 used. John