Why are 6V6G(T)'s always black inside?

Circlotron · 24th November 2003, 09:24 AM

Every one I have ever seen is always black on the inside surface of the glass envelope. Even ones with relatively little use. Whyzat?

fdegrove · 24th November 2003, 03:29 PM

Hi,

Quote:

Every one I have ever seen is always black on the inside surface of the glass envelope. Even ones with relatively little use. Whyzat?

Most older 6L6G had this coating as well.
Not all 6V6s do have that coating (graphite) though, the USSR ones for instance don't have this.

6L6 STORY

At the bottom of page are some 6V6 pictures.

Note also that not the entire glass is coated, it just grows darker with ageing because of the gettering.

Now as to why this was done, I don't know but I could try to find in explanation in my tube history books....

Cheers,

Sch3mat1c · 24th November 2003, 05:15 PM

I've got some new looking Magnavox 6V6s that don't have the coating. Small cylindrical ribbed plate, gray color. They look real neet.

I seem to remember the explanation is the glass they used to use was too good an insulator, so electrons which got away from the plate and struck the envelope (giving the blue glow) built up a charge, and over time this would have bad effects on the glass. So they put conductive graphite inside to provide leakage current.

Or maybe they did it to increase IR absorbtion, allowing more plate dissipation. Who knows.

Tim

fdegrove · 25th November 2003, 01:45 AM

Hi,

Quote:

I seem to remember the explanation is the glass they used to use was too good an insulator, so electrons which got away from the plate and struck the envelope (giving the blue glow) built up a charge, and over time this would have bad effects on the glass. So they put conductive graphite inside to provide leakage current.

You're going to have a hard time explaining, mister.

You don't make any sense here, junior.

Cheers,

Brett · 25th November 2003, 02:02 AM

Why are 6V6G(T)'s always black inside?

To give a dark tone?

fdegrove · 25th November 2003, 02:08 AM

Hi,

Quote:

To give a dark tone?

LOL...

I think it has more to do with the glass not being baked...

Could be wrong though....

Cheers,

Brett · 25th November 2003, 02:13 AM

Frank,

I dunno why it's dark either. Perhaps the designer had a fondness for Guinness.

Now of my collection of NOS GE and RCA 12V6's have anything but clear glass.

fdegrove · 25th November 2003, 02:31 AM

Hi,

Quote:

I dunno why it's dark either. Perhaps the designer had a fondness for Guinness.

With my fondness for the occasionnal Guinness?

Rest assured, it IS the glass that made them use the coating.

Secondary emission comes to mind with impurities in the bottle...too young to quote this from the top of my head though...

Pretty sure I'm not too far off base.

Cheers,

Sch3mat1c · 25th November 2003, 03:13 AM

Quote:

Originally posted by fdegrove
You're going to have a hard time explaining, mister.

You don't make any sense here, junior.

Hey, it's just what I heard. Doesn't make much sense to me either.

Tim

SHiFTY · 25th November 2003, 03:58 AM

I have a whole lot of tubes that are black inside, certainly a lot of JAN ones seem to have the black coating. Maybe the army liked the blackout look

I think it was to make them look more like the metal tubes of old...

24th November 2003, 09:24 AM	#1
Circlotron diyAudio Member Join Date: Jun 2002 Location: Melbourne, Australia	Why are 6V6G(T)'s always black inside? Every one I have ever seen is always black on the inside surface of the glass envelope. Even ones with relatively little use. Whyzat?

24th November 2003, 05:15 PM	#3
Sch3mat1c diyAudio Member Join Date: Jan 2003 Location: Milwaukee, WI	I've got some new looking Magnavox 6V6s that don't have the coating. Small cylindrical ribbed plate, gray color. They look real neet. I seem to remember the explanation is the glass they used to use was too good an insulator, so electrons which got away from the plate and struck the envelope (giving the blue glow) built up a charge, and over time this would have bad effects on the glass. So they put conductive graphite inside to provide leakage current. Or maybe they did it to increase IR absorbtion, allowing more plate dissipation. Who knows. Tim __________________ Seven Transistor Labs Projects and Resources

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
what do you think about this amp? (pic inside)	audioholik	Solid State	9	17th November 2006 10:50 AM
6V6G recommended schematic	Salas	Tubes / Valves	36	6th February 2006 02:37 AM
6v6g	gianis	Swap Meet	0	8th January 2006 06:38 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

25th November 2003, 02:02 AM	#5
Brett diyAudio Member Join Date: Jan 2002	Why are 6V6G(T)'s always black inside? To give a dark tone?

25th November 2003, 02:13 AM	#7
Brett diyAudio Member Join Date: Jan 2002	Frank, I dunno why it's dark either. Perhaps the designer had a fondness for Guinness. Now of my collection of NOS GE and RCA 12V6's have anything but clear glass.

25th November 2003, 03:58 AM	#10
SHiFTY diyAudio Member Join Date: Jul 2002 Location: New Zealand	I have a whole lot of tubes that are black inside, certainly a lot of JAN ones seem to have the black coating. Maybe the army liked the blackout look I think it was to make them look more like the metal tubes of old...