Udbrændte rør??

[Mataugust]

Jeg har lige sat andre rør i min Little Dot, og det gav en forbedring der var så massiv, at jeg næsten ikke selv kunne tro det. Så nu oververjer jeg om det simpelthen var fordi de andre rør var udbrændte/flade. Er det noget der kan ses på dem hvis de er? De gamle rør er delvist sorte på toppen af noget der minder om sod (se billedet).


Nogen der ved så meget om rør at de kan forklare det?

[librarian]

Rør bliver bare bedre og bedre indtil den dag, de dør, og så kan de slet ikke sige noget. Det er i hvert fald hvad jeg har læst mig frem til... Men der kan selvfølgelig være fejl på rør. Nogle støjer f.eks. mere end andre...

[librarian]

Og rør kan sagtens have misfarvning uden at det har betydning for lyden

[Buyer no 1]

Med mindre misfarvningen er hvid, hvilket indikerer at røret ikke længere holder vacum, og dermed ikke vil fungere.

[Claus-DK]

det sorte er det ikke noget fra de plader der er i røret der er fordampet ??
Det synes jeg at have læst..

Et rør brænder generelt ikke ud de er skabt til at kunne virke i mange tusinde timer og med den begrænsede tid vi har strøm på dem i vores forstærkere burde det ikke betyde noget som helst..

[Solderdude]

The black (silverish) is not from using the tube / wear and tear.

It is the result of eliminating the last bit of air molecules that have remained after being sucked vacuum in the production process.
When the tube is 'sucked' empty on manufacturing there will always be some air molecules left in the tube.
This is not wanted.
For this they have inserted a 'getter'.
It is a metallic ring (sometimes oddly shaped) that has material on it that reacts with air when heated.
When the tube has been sealed (glass pipe, mostly on top melted) a coil outside of the tube creates a strong magnetic field that induces a large current in the getter ring, thereby evaporating the getter material on it.
This material reacts with the remained trapped air molecules and deposits this on the glass in a flash.
Mostly on top of the tubes, but sometimes on the side, in any case near the getter.

When turned white (as shown in the pic above) it means vacuum is breached and the tube is defective.

Tubes wear down over time, some gradual, some stay strong for long periods others drop fast.
Some new JJ tubes get bad really quick, some older tubes last very long.
There is no telling not even when someone has measured them a few minutes before, you simply cannot predict lifespan of a tube.

The only way to tell is by measuring them or using them and checking plate voltages.
Tubes may get noisy or crackling when damaged or getting in a faulty state or simply loose emission and thus will not work properly.
Mostly bass performance is affected first as this has the largest voltage swing in a music signal and thus will 'clip' first.