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Slight grey shadow around el84 tube near the top just under the getter ... is this OK?

post #1 of 10
7/20/11 at 10:02am
Thread Starter 

Here are some photos ..the first two is the tube with the shadow and the other is a tube without ... is this a sign or a problem or is it normal ? Both are used tubes but are matched and will be used together in my amp.

    Thank You in advance ... bigsmile_face.gif

 

 

 P1140834_2122x1591.jpgP1140835_2122x1591.jpgP1140838_2122x1591.jpg

 

 

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post #2 of 10
7/20/11 at 3:02pm

That tube looks OK.  I pulled some 6BQ5's out of an old Dynaco that looked ten times worse and lasted for a couple years.  If it sounds OK, you should be alright. 

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post #3 of 10
7/20/11 at 3:08pm
Thread Starter 

Thank you for your reply Irishsammy ... I was wondering what the grey area is ... is it some sort of vapor deposit  or whatever ... because none of my other tubes have this cloud like stuff on the inside ... since i have started this hobby I have learened a lot and obviously still have a lot more to learn ... but its fun!

 


Edited by dancingpotato - 7/20/11 at 3:11pm
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post #4 of 10
7/20/11 at 3:11pm

I'm no tube historian mind you, but I think there are quite a few things going on during tube manufacture that might explain that.  Your mention of a vapor deposit is what I would guess, too.  When they add the silver tops to those tubes, I'm sure whatever they use (mercury?) can cause some of that cloudiness. 

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post #5 of 10
7/20/11 at 3:23pm
Thread Starter 

These tubes are supposed to be a matched set ... so why would just one have this cloudy stuff? I am sure some of the tube gurus on here would know ...

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post #6 of 10
7/20/11 at 3:33pm

These tubes were manufactured over several decades. You probably have tubes from different batches that were constructed slightly differently. I have 6BL7GTA tubes, for instance, that had all kinds of construction differences and some were manufactured only months apart.

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post #7 of 10
7/20/11 at 5:39pm
Thread Starter 
Quote:
Originally Posted by sacd lover View Post

These tubes were manufactured over several decades. You probably have tubes from different batches that were constructed slightly differently. I have 6BL7GTA tubes, for instance, that had all kinds of construction differences and some were manufactured only months apart.


Both tubes have exactly the same construction ... but one has that greyish band of some sort of deposit ...  and that is what I am trying to find out about.

 

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post #8 of 10
7/21/11 at 9:16am

 

This light grey shadow appears to be common since I see this allot with GE tubes. Just check the pictures on Ebay. The getter flash which is usually a form of Barium alloy creates a metal vapor silver like deposit on the top of the tube which helps to absorb the remaining air in the tubes. As long you still have the silver appearance the tube is good.

 

  http://cgi.ebay.com/GE-EL84-MATCH-PAIR-6BQ5-COPR-GRID-POST-NOS-NIB-/230648573193?pt=Vintage_Electronics_R2&hash=item35b3b9ed09 

 

or this?

 

http://cgi.ebay.com/Pair-Siemens-E84L-Audio-Tubes-Pro-EL84-6BQ5-NOS-/220712429761?pt=Vintage_Electronics_R2&hash=item33637c68c1

 

 

http://cgi.ebay.com/4x-MULLARD-EL84-6BQ5-BLACKBURN-BEST-LEAK-STEREO-20-/200630630581?pt=Vintage_Electronics_R2&hash=item2eb68478b5 

 

 

 


Edited by john57 - 7/21/11 at 10:05am
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post #9 of 10
7/21/11 at 1:45pm
Thread Starter 
Quote:
Originally Posted by john57 View Post

 

This light grey shadow appears to be common since I see this allot with GE tubes. Just check the pictures on Ebay. The getter flash which is usually a form of Barium alloy creates a metal vapor silver like deposit on the top of the tube which helps to absorb the remaining air in the tubes. As long you still have the silver appearance the tube is good.

 

  http://cgi.ebay.com/GE-EL84-MATCH-PAIR-6BQ5-COPR-GRID-POST-NOS-NIB-/230648573193?pt=Vintage_Electronics_R2&hash=item35b3b9ed09 

 

or this?

 

http://cgi.ebay.com/Pair-Siemens-E84L-Audio-Tubes-Pro-EL84-6BQ5-NOS-/220712429761?pt=Vintage_Electronics_R2&hash=item33637c68c1

 

 

http://cgi.ebay.com/4x-MULLARD-EL84-6BQ5-BLACKBURN-BEST-LEAK-STEREO-20-/200630630581?pt=Vintage_Electronics_R2&hash=item2eb68478b5 

 

 

 

Hi John57,  It does look like this tube (right) in the second photo ... it may be common but none of my other 26 or so tubes have this ring ... and my tube in question is a Sylvania so this phenomena crosses party lines ....

 

Shadow1.jpg

 

 

http://cgi.ebay.com/Pair-Siemens-E84L-Audio-Tubes-Pro-EL84-6BQ5-NOS-/220712429761?pt=Vintage_Electronics_R2&hash=item33637c68c1

 

 

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post #10 of 10
7/21/11 at 2:47pm

Yes it seems to cross manufacture lines. The point is that this ring seems to happen at the time of manufacture not after the time the tube is in operation for some time. It seems that some of the Barium alloy in the getter when super heated by RF induction during manufacturing reacted to a bit of more gasses that was in the tube and formed the ring. If the ring was turning white or the silver colored metallic deposit becoming clear in time that I would be concerned about it. I find that the silver coating to be very uneven in some of my other tube types. I do not have all the answers and there is something always to learn in this hobby.  on

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