[jules]

I bought this tube on ebay



in my opinion it's used, not used to death but certainly not new ... any opinions out there?

jules

[Dan Driscoll]

It can be hard to tell with tubes, especially if they are NOS. What specifically makes you think it is used? Fading or wear on the lettering isn't a reliable determiner of whether a tube is used, that can happen just through age or rubbing against the inside the tube box. I can't be sure, but in the photo the pins don't seem to have any noticeable wear.

[JoshK]

incredibly hard to tell as Dan suggests.  If it tests and operates like new it, for pratical purposes, is new.  Usually the getter and flashing are the parts that get worn down.  If the flashing isn't shiny anymore, it is a sign it has had some use. 

Lettering wear is no indication of use.  Neither is oxidation on the pins, as this happens even in storage.  We can't see the getter in this picture, but the flashing looks clean and shiny.  Looks all around the top for signs of wear in the flashing above the getter.   I'd also look at the filament closely if you can see it, but I am not sure exactly what to look for, as filaments can be made of a number of things.  Look for inconsistencies in the filament.  But that could also be from production rather than use.

The tube looks fairly clean, so testing the tube is the only way to know if it is like new. 

[Joey B]

Take the tube and have it tested . If it measures new ,it is . If it measures below , it is old stock , not new old stock .

Joe

[jules]

The things that make me think it's used are:

a) the gray deposit on the inside of the glass below the getter.

b) the getter is not as shiny as a new tube

c) there are flecks of material on the inside of the glass. Tiny fragments that I understand indicate breakdown of some elements

d) there is blackening at the point where the pins connect to wire inside the tube [this happens relatively quickly in use but it does indicate that use has occurred. I've got some tubes I've been using for 100hrs that show no sign of this scorching]

A test would be interesting but as far as saying that if it tests new it is new, I don't agree that it's definitive. I've got a set of very used Siemens tubes that still measure fine though I'm in no doubt they've got less life in front of them than behind them.

Yes Josh, I've got no idea how to spot the filament  . In this case I think it might be entirely shielded.

jules

ps: the lettering is interesting but had nothing to do with my judgment. As you can see, there's no brand and I think they are most probably Siemens military items. I also think it's possible that these have been replaced after a specified number of hours use ... this is purely speculation though

[jules]

I imagine different tubes are going to age in slightly different ways but for reference, here's a new Siemens tube of a very similar type [source: tubemonger library]




the lower edge of the internal black cap is very sharply defined and the getter is visible with a slight gap of light between it and the "cap". In the first photo I posted, the edge of the "cap" blends into the deposits, obscuring the getter and getting fainter as it extends down the tube.

Thanks everyone for your opinions. It doesn't seem as though it's clearcut, at least from a photo.

jules

[JoshK]

I wouldn't count myself among the tube experts.  I would say to ask this question over at diyaudio's tube forum to get some really experienced guys' opinions.  They have seen thousands of tubes and have went through their fair share.  I just shared what little I've read. 

[JoshK]

The filament pins are #4 & #5....trace the inside leads of these pins to try to see where they go....ultimately to the filament.  This is likely in the center of the plate which wraps around the cathode, but sometimes you can see part of it. 

[jules]

hmmm ... yes, just checked what I can see of the filaments on two tubes. My very used Siemens has filaments that look fine [but it's got a massive amount of deposit inside the top of the glass]. The old Siemens is also free from the rather worrying flecks of material inside the glass.  You can see the largest of these in the photo. The filaments on the tube in question also looks ok ... seems inconclusive.

Your opinion on this is most appreciated Josh.

It seems as though opinions on this are going to be varied, particularly when the judged from a photo. I doubt there's much I can do about it but tube clouding will be one of my major tube evaluating tools in the future even if it is hard to quantify.

jules

[JoshK]

I don't think the rattling bits inside the tube are troubling or even a sign of age.  I could be wrong, but I think this can happen in the manuf. process.  The deposit of crap around the flashing and getter is more telling.  Your older siemen's build up is consistent with useage. 

[jules]

The deposit of crap around the flashing and getter is more telling.  Your older siemen's build up is consistent with useage.

Yes ... that's the essence of my doubt about the tube. The pattern of "buildup" is light but in the same pattern/place as the older tube.

jules