I just happened to notice with the lights off, that the 42 and 80 tubes had blue light patches on them with the radio on. Looks cool, but what is this, bad or good? Is this why sometimes you can hear a hiss at times with the volume down.

Hi,
Yes, this is a likely the source for the hiss. It is ionizing gas that you are seeing. This tends to increase current draw, I would be inclined to replace both of those tubes and only try them in another radio if the glow is absolutely minimal. But they will never get better.

:I just happened to notice with the lights off, that the 42 and 80 tubes had blue light patches on them with the radio on. Looks cool, but what is this, bad or good? Is this why sometimes you can hear a hiss at times with the volume down.

I should add too that any radio that such a tube found service in, would be one that would never be left unattended, and would also be checked frequently when in operation, and would be operated minimally. The gassy tubes can be significant fire hazards, but still are useful for testing purposes in old radios that are being serviced. You do not feel it a loss if you burn out a tube that had been glowing, but you get more than just annoyed when you burn out a tube fresh from the NOS box.

:Hi,
:Yes, this is a likely the source for the hiss. It is ionizing gas that you are seeing. This tends to increase current draw, I would be inclined to replace both of those tubes and only try them in another radio if the glow is absolutely minimal. But they will never get better.
:
:
::I just happened to notice with the lights off, that the 42 and 80 tubes had blue light patches on them with the radio on. Looks cool, but what is this, bad or good? Is this why sometimes you can hear a hiss at times with the volume down.

:Fire hazard, why ....the 42 tube I just bought from PTOP. If I keep playing them what would happen or possably. Are tubes gassey that way from the factory or do they get that way over time or operation. Well I have heard of gassey tubes but never knew what one does or looks like...so at this point I am supposed to be annoyed. When I turned up the volume loud, the blue went away. Turning off the radio and back on made it go away too. They draw too much current..hmmm, overheats the power transformer which is the reason for fire hazard?
:
:I should add too that any radio that such a tube found service in, would be one that would never be left unattended, and would also be checked frequently when in operation, and would be operated minimally. The gassy tubes can be significant fire hazards, but still are useful for testing purposes in old radios that are being serviced. You do not feel it a loss if you burn out a tube that had been glowing, but you get more than just annoyed when you burn out a tube fresh from the NOS box.
:
:
::Hi,
::Yes, this is a likely the source for the hiss. It is ionizing gas that you are seeing. This tends to increase current draw, I would be inclined to replace both of those tubes and only try them in another radio if the glow is absolutely minimal. But they will never get better.
::
::
:::I just happened to notice with the lights off, that the 42 and 80 tubes had blue light patches on them with the radio on. Looks cool, but what is this, bad or good? Is this why sometimes you can hear a hiss at times with the volume down.

From "Sylvania Engineering Data Service", vol. 1, pg 23 (1960?):
BLUE GLOWS
Blue Glows are not tube detriments per se. They are, however, suspects in the eyes of many receiving tube users for lack of a full understanding of their origins. There are several types of Blue Glow which can be described as follows:
FLUORESCENCE-this type of glow is usually violet in color and most noticeable around the inside surface of the glass bulb. It is most pronounced on power tubes and is the product of electron bombardment of the glass taking place within the tube. It generally has no adverse affect upon receiver performance, and in fact, tubes displaying this phenomenon are particularily good with respect to gas content.
MERCURY VAPOR HAZE-is a blue-violet glow associated with those tube types which rely upon mercury vapor for proper operation. In such cases, the blue glow should be evident indicating proper operation.
GAS-produces a blue haze, generally confined to the vicinity of the mount structure. The proper function of gas types such as thyratrons, voltage regulator and voltage reference tubes, requires the presence of this glow as an indication of proper tube operation. Some voltage regulators use neon instead of argon and as a result exhibit a pink-orange glow. It is, however, a distinct detriment in vacuum receiving types, where the presence of gas in large amounts can cause malfunction of the equipment.

Tubes operate on the principle of thermionic emmission. A heater filament heats the cathode until it glows a dull red. The cathode is made of materials that can emit electrons at high temperature. The tubes plate is held at a high positive voltage, which attracts the electrons emitted from the cathode. In amplifier tubes, the flow of electrons is controlled by one or more fine wire screens or grids placed in between the cathode and plate. The flow of electrons is controlled by varying the voltage applied to the grid. A small change in grid voltage results in a larger change in electron flow through the tube, amplifying the signal applied to the grid.
Many materials flouresce or "glow" when struck by electrons. Not all the electrons in a vacuum tube strike the plate. A few stray off and strike other things in the tube, such as the glass envelope. Many types of glass will give off a faint blue glow when bombarded by electrons of sufficient energy. This is the most common type of blue glow seen in power output tubes. Often you will see small patches of glow that correspond to the holes in the plate or other structures in the tube.
Another type of glow you may see in power tubes appears on the inside surface of the plate structure. The pattern of the glow will aften appear in strips that vary along with the signal applied to the tube. (i.e., the music.) This type of glow is generally normal as well. It is often caused by a thin layer of atoms that have boiled off the cathode and deposited on the surface of the plate. What you see is the slight flourescence of this material when it is hit by electrons from the cathode. The stripes correspond with the alignment of the grid wires. The varying widths of the stripes demonstrate the operation of the tube. The grid allows restricts the size of the electron beam according to the grid's voltage.

Hi Sean

Gassy tubes, like John mentioned, draw too much current, cause distortion and can damage other components in a radio.

Not all tubes with blue glow are gassy. If blue is within the elements that's a gassy tube and shouldn't be used. Sometimes you will see blue just inside the glass. Blue like this is caused by an electron beam hitting at that point. Tubes like this are good..

You had mentiond an 80 with blue glow. Look between the plate & filament. If it glows blue in that area the tube is gassy.

Norm

::Fire hazard, why ....the 42 tube I just bought from PTOP. If I keep playing them what would happen or possably. Are tubes gassey that way from the factory or do they get that way over time or operation. Well I have heard of gassey tubes but never knew what one does or looks like...so at this point I am supposed to be annoyed. When I turned up the volume loud, the blue went away. Turning off the radio and back on made it go away too. They draw too much current..hmmm, overheats the power transformer which is the reason for fire hazard?
::
::I should add too that any radio that such a tube found service in, would be one that would never be left unattended, and would also be checked frequently when in operation, and would be operated minimally. The gassy tubes can be significant fire hazards, but still are useful for testing purposes in old radios that are being serviced. You do not feel it a loss if you burn out a tube that had been glowing, but you get more than just annoyed when you burn out a tube fresh from the NOS box.
::
::
:::Hi,
:::Yes, this is a likely the source for the hiss. It is ionizing gas that you are seeing. This tends to increase current draw, I would be inclined to replace both of those tubes and only try them in another radio if the glow is absolutely minimal. But they will never get better.
:::
:::
::::I just happened to notice with the lights off, that the 42 and 80 tubes had blue light patches on them with the radio on. Looks cool, but what is this, bad or good? Is this why sometimes you can hear a hiss at times with the volume down.

:Once again john, norm and easyrider to the rescue. Yes the blue is "just inside the glass itself. So translated this means I can use my tubes...normally. The 42 glows pretty good(on the glass itself in various spots on the tube), not in the tubes elements....I was just about to return the 42 tube to PTOP, NOT now. I have discovered yet another "cool radio phenomena"...I will now turn off the lights and stare at the philco,,,from the back.
:
:but if the tubes just glow on the glass itself, what causes the intermittent soft hiss..turning the radio volume up and back down suddenly a couple of times gets rid of the hiss
:
:Hi Sean
:
: Gassy tubes, like John mentioned, draw too much current, cause distortion and can damage other components in a radio.
:
: Not all tubes with blue glow are gassy. If blue is within the elements that's a gassy tube and shouldn't be used. Sometimes you will see blue just inside the glass. Blue like this is caused by an electron beam hitting at that point. Tubes like this are good..
:
: You had mentiond an 80 with blue glow. Look between the plate & filament. If it glows blue in that area the tube is gassy.
:
:Norm
:
:
:::Fire hazard, why ....the 42 tube I just bought from PTOP. If I keep playing them what would happen or possably. Are tubes gassey that way from the factory or do they get that way over time or operation. Well I have heard of gassey tubes but never knew what one does or looks like...so at this point I am supposed to be annoyed. When I turned up the volume loud, the blue went away. Turning off the radio and back on made it go away too. They draw too much current..hmmm, overheats the power transformer which is the reason for fire hazard?
:::
:::I should add too that any radio that such a tube found service in, would be one that would never be left unattended, and would also be checked frequently when in operation, and would be operated minimally. The gassy tubes can be significant fire hazards, but still are useful for testing purposes in old radios that are being serviced. You do not feel it a loss if you burn out a tube that had been glowing, but you get more than just annoyed when you burn out a tube fresh from the NOS box.
:::
:::
::::Hi,
::::Yes, this is a likely the source for the hiss. It is ionizing gas that you are seeing. This tends to increase current draw, I would be inclined to replace both of those tubes and only try them in another radio if the glow is absolutely minimal. But they will never get better.
::::
::::
:::::I just happened to notice with the lights off, that the 42 and 80 tubes had blue light patches on them with the radio on. Looks cool, but what is this, bad or good? Is this why sometimes you can hear a hiss at times with the volume down.