Matsushita 6qb5..does milk equal toast

J

Jeanluc

Active Member
Pulled these Matsushita 6qb5s from a recently acquired Lafayette LA-224a and am wondering if a quick visual inspection is a good indicator of their likely being in poor condition.

In my short experience in the tube realm I have not yet encountered this "milky" phenomenon on any of the tubes I've happened upon. A quick web search suggests this may be an example of tubes with a " violated integrity" or that of foreign particles remaining in the vaccuum.

In either case I'd like to know how you all would regard tubes which you found in this condition.

Should I consider them faulty or soon-to-fail?
If I were to give them a listen an I potentially endangering my amp and if so what exactly could happen?
Thanks in advance
 

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Hard to judge by the picture, but can be yellow paint ?

Painted may mean they where matched or low noise selected or matches some kind of critera.

Try to remove the paint using Acetone, and don't touch Acetone with your skin, use rubber gloves, also, don't inhale, do this in a vented environment.

It they are white internally they lost vacuum, but they do not appears to be whitened getters.
 
mroboto said:
Hard to judge by the picture, but can be yellow paint ?

Painted may mean they where matched or low noise selected or matches some kind of critera.

Try to remove the paint using Acetone, and don't touch Acetone with your skin, use rubber gloves, also, don't inhale, do this in a vented environment.

It they are white internally they lost vacuum, but they do not appears to be whitened getters.
Click to expand...

A bit more description... the color resembles something more of an off-white frosting if you will. To the touch there seems to be a textural difference with the surrounding mirrored surface.
An additional element that leans more toward its being internal is that the milky-ness extends to the tip of the nib. Somehow it doesn't seem to me that one would do this if intending to simply apply a differentiating mark of some.

Let me take a stab at a better pic... 1493259476206-396228357.jpg 1493259476206-396228357.jpg
 
Gadget73 Thanks for the picture, it is a good example, but how does vacuum leak out? Is not the internal pressure of a vacuum tube much less than normal air pressure. It is not air leaking in rather than vacuum (the absence of air/gasses) leaking out?



Okay, I know that I am just being pedantic. :D:D:D
 
I LIKE MUSIC said:
how does vacuum leak out?
Click to expand...
A joke. "Gone to air" is another way of saying it. Either way it means the tube is not under vacuum any longer. When the getter oxidizes, it turns white. Its normally a dark color, indicating that the tube hasn't been exposed to air internally.

Your pics look like some sort of dirt or paint on the outside of the tube.
 
Jeanluc said:
If you look at the new pic i included a few posts up, does this seem to be a similar situation?
Just located a rubber glove to give rhe area a wipe with acetone.
Click to expand...

That does look like someone marked the tube for some sort of sorting or grading purpose (to make matched sets or to mark tubes for a specific purpose at the manufacturing plant).

I'm betting that it will come off with acetone or some other solvent.

Regards,
Gordon.
 
GordonW said:
That does look like someone marked the tube for some sort of sorting or grading purpose (to make matched sets or to mark tubes for a specific purpose at the manufacturing plant).

I'm betting that it will come off with acetone or some other solvent.

Regards,
Gordon.
Click to expand...

Gordo gets the prize. The acetone wiped it clean.
So my takeaway is therefoe to assume that this was simply part of a marking system of some sort.
 
If all four were marked this way, I would think that it would be pretty much a sure thing that they were originally a matched set. I'd still measure to see if they still match reasonably well, but there's a good chance they'd still be a working matched set.

Regards,
Gordon.
 
GordonW said:
If all four were marked this way, I would think that it would be pretty much a sure thing that they were originally a matched set. I'd still measure to see if they still match reasonably well, but there's a good chance they'd still be a working matched set.

Regards,
Gordon.
Click to expand...

Only the red/orange Baldwin/Matsushita were marked as such. The white labeled pair were unmarked. All are of the ribbed plate, o-getter variety. Do you have any idea as to in what way the two pairs may be differentiated?
 
Two of them may have been replaced.

Two pairs, however, is still good, as long as they're all the same brand and construction inside. That would work fine.

Regards,
Gordon.
 
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