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OLD VACUUM TUBE QUESTION

N

nightfly61

Guest
As much as I wish I did, I know next to nothing about vacuum tubes- except that I have a LOT of them new and used. Some are in boxes that look like new, but the tube themself has that silver or sometimes greyish black color inside the glass.
Is it safe to say that any tube that has that "burnt glass" color inside the glass has been used at one time or another? If so, why wouldn't the old engineers just pitch the one that was going bad instead of saving it?
I know some are new because the boxes haven't been opened, but I just opened a big RCA 810 box with the tube still in it's brown cotton shrowd wrapping & it has a top AND a side connector lookin thing (it is a beautiful tube!), but it also has some silver color on the glass inside. Can someone tell me if these are new or used please? I'm trying to figure out what to do with them all & there's nowhere near where I live that has a tube tester (some of these are way too big for one of those anyway. Thanks again. Nightfly
 
The discoloration inside the tube is normal, even for a new tube. When a tube is manufactured, a vacuum is pulled to remove the oxygen inside that would otherwise diminish the life of the filament. Remember what happens to a light bulb when the glass envelope is broken when it's on? The bulb burns very brightly for a very short time. Same thing for the tube filament. The tube is manufactured with a "getter." The coating you see is the remnant of that. See http://en.wikipedia.org/wiki/Getter.
 
the discoloration is a result of activation of the 'getter'

it is called that because it 'gets' the gasses that are given off during the sealing / filament testing and combines with those gasses, fixing them in non-gaseous form so as not to contaminate the vacuum and cause early filament failure or arc-overs

here's some info

http://www.hans-egebo.dk/Tutorial/tubes.htm

a little over half-way down the page

G
 
Don't suppose you have any 12AX7, 12AT7, 6V6, or 6L6's in that lot? I tinker with guitar amps - those are common tubes I look for.
-D
 
dtube1 said:
Don't suppose you have any 12AX7, 12AT7, 6V6, or 6L6's in that lot? I tinker with guitar amps - those are common tubes I look for.
-D
Click to expand...
I have: 1 GE 12AT7
1 RCA 6L6
1 RCA 6V6 GT
 
Getter will usually be opaque and looks like a mirror. Its sprayed on the inside of the glass.

Some larger transmitting tubes (4-250's, 4-400's, 3-400z, 3-500z, 4-1000, for example) don't usually have getter, but the glass will be discolored (transparent...looks like the glass changed color) by use in the transmitter (used tubes!)

The "old engineers" were frugal, and would keep old, soft tubes for use in an emergency to keep broadcasting.
That doesn't mean they have much value in any other situation.
 
dtube1 said:
Oh crud, I was hoping for a carton or two :'( . Ebay will be your friend with those tx tubes.
-D
Click to expand...
A dealer online made me a decent offer for the whole bunch of them, but then I went to another site that had a price list & my jaw dropped at their actual value of some. One's worth $90.00 alone & the big 810s & 813s are valued at over $100 each. Some came from my old station that got a new xmtr & others came from an old movie theatre projection room before they tore it down. Thanks very much everyone for answering my questions! :)
 
If you happen to have any 8950s around those will bring a good price. NOS 8950s go for around $75- $90 each. They were popular in Swan and Siltronix ham gear, and the tube of choice for most old Palomar amps (and their derivatives) Unlike many tubes there is no direct replacement for them.

You may be sitting on a gold mine!
 
I thought I read the getter was deposited (condensed, actually) near a particular wire structure brought near the glass envelope.
During the vacuum, baking and irradiation process to drive off gasses, the getter is a gas.
The mercury condenses and being highly reactive with common gasses, the few atoms of other gasses are taken up in the getter.
Silver is good, brown is a well-used tube that may or may not still work, white means the vacuum is lost.
Naturally there are dozens of factors in whether a tube is any good, but that's what the getter can tell you.

I've been collecting tubes for 30 years, mostly 1920's-1950's radio types, for my own collection of radios.
But maybe it's time to sell some..
 
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