blue glow, how?

[newtube]

What makes a tube glow blue guys?
is there a particular kind of tube that glows more than others?

Reason i ask is my tubelab sse has chinese 6l6gc tubes that glow with a little blue just after startup but fades after a few seconds but some images i see on here are just divine!

Its purely an asthetic thing but it would be nice to see the blue all the time

[SGregory]

My EH kt88 have a nice blue glow on the glass.
Where is the blue glow coming from. Some is asthetic andother times can be spectacular (when it fries)

[tomchr]

Unless you're talking about mercury vapor rectifiers -

or voltage regulator tubes -

the blue glow you refer to is caused by electrons that are accelerated past the tube structure and hits the glass envelope, where it excites impurities in the glass.

I'm running with a small sweep tube power amp using a 6LU8 tube. One is a Westinghouse brand and does not exhibit the blue glow. The other is an RCA branded tube and this one does glow blue around the pentode section. Increasing the anode voltage increases the amount of blue light emission as the electrons flowing in the tube are accelerated to higher velocities due to the higher anode voltage. This causes more of them to leave the tube structure and hit the glass... The higher anode voltage is not a desirable operating point from a distortion stand point, though.

I'm guessing the reason your tubes glow blue on start-up and then fade is because it takes a while for the bias voltage to stabilize.

If you really, really want blue light, you could pull the tacky, el-cheapo Chinese eBay amp trick and add a blue LED below the tube socket... Or you could buy a bunch of 6L6'es of different brands and see if you can find any that glow blue in your amp.

~Tom

[Wavebourn]

I know that some Russian 6P3S tubes have a glass that glows blue when bombarded by electrons.

[TheGimp]

6P1P is notorious for blue glow along the screen rods inside the tube.

Then there is the occasional blue glow that is not good:

[rotaspec]

The 5B/254M produces a nice glow around the glass. See here:
CV428 or 5B254M useful?

Just for fun I hooked one up on the bench this morning and even at 200v/35mA plate it produced a faint blue ring around the glass extending about 3/4" up from the base of the plate structure.

Gary

[tubelab.com]

My EH kt88 have a nice blue glow on the glass.

Mine did when I got them, but now 2 years later they still rock, but don't glow much.

[SpreadSpectrum]

EH 7591s

[newtube]

Thats the stuff i mean spreadspectrum! its beautiful, i want mine to do that

[rknize]

SED KT88s have a very pleasant blue glow on the glass. Not as apparent in the pic, but strong in person:



Their EL34s also glow, especially near the screens.