Tube silvering?

[JamieMcC]

Recently I was able to get hold of some NOS tubes these have completely clear glass, I also noticed compared to my current used ones, the plates have a sort of textured powdery coating to them while my current ones are smooth.

I plugged one in to my Crack to check all was ok and over say 20 minutes you could see the clear glass start taking on that silvering colour. I wondered is this some kind of deposition of what ever the powdery coating covering the plate is to the glass and if some sort of general minimum temperature or initial length of running is required to maximise this burning off to optimise the tubes characteristics?

Any correct terms for the above as I would to like to read up a bit so I have a better understanding of what is happening?
 
Cheers Jamie

[Paul Birkeland]

None of this sounds particularly promising. 

See 4:25 in this video for how getters are generally formed:

I have seen references to getters being made in the manner that you're referring to - where the plate is superheated and a deposition is formed on the inside of the glass, but I haven't ever seen references to this in any of the tube variants that go into the Crack.

There are also certain tubes with plates that act as getters if they are run hot enough. 

[JamieMcC]

Hi Paul thanks for your help that video was interesting. The tubes are the Tung-Sol 5998 type here is a pic of the different stages.

NOS tube far left is still quiet clear I just ran it for 15 mins in the BHC to test and it sound super with no noise or microphonics. Not sure if you can see but the anode plates are dull and have fine coating? to them)

NOS Middle tube I ran for about 30 mins and you can see the silvering starting to form around the bottom of the tube. The anode plates have started to lose some of the dullness, again sounds great no noise or microphonics.

Tube far right this is a tube which arrived with silvering full tested (Amplitrex AT1000) supplied with readings tested as new or better from dealer (TC Tubes) who in addition to the Amplitrx use a OTL headphone amplifier (looks like a BH product) to screen for excessive noise and microphonics as well.  TC tubes have been great to deal with by the way.

This tube I have about 100hrs on and arrived with silvering note the shiny anode plate.

I am just curious to the process which seems to be happening.

(https://www.head-fi.org/image/id/5521889/width/900/height/900/flags/LL)

[Paul Birkeland]

They all have gettering at the top, so I wouldn't sweat it.