Re: [neonixie-l] OT: Darkened NOS(?) RCA 6AH6 tubes?

Sat, 16 Jan 2016 08:32:26 -0800

First some clarification. "IF" the darkened coating is EVENLY distributed around the inside of the glass, and totally surrounds all of the internal structure of the tube, it is quite possibly a deliberate smoke coating deposited there at the time of manufacture to make the tube less susceptible to outside light. Outside light does affect the operation of almost all tubes, to a lesser or greater degree. This smoke coating was quite often seen, and used to reduce this effect. Ira. 

On 1/16/2016 4:04 AM, 'marta_kson' via neonixie-l wrote:
As this group has a deep understanding and waste knowledge of hollow state devices, I would like to ask for an opinion about the state of those tubes pictured in the link below. 


They are RCA 6AH6 that appears on the market from several sources, 
claiming they are NOS/NIB. Are there any possibilities the blackening 
on the inside of the glass have been deposited as part of manufacture? 
On one tube in particular there are clear lines visible in the black 
material, as it has been rubbed off by the mica wafer when it was 
inserted. If so, they was clearly dark from the factory.



Nevertheless, it's a foreign matter present inside the tube. Are there 
any reason to belive they are of inferior quality?
Unfortunately I have no tube tester, but listening tests on a receiver 
with those as RF and first mixer gives an impression they offer more 
noise and less amplification. I don't trust my own judgement there, as 
knowing what is in the sockets definitely puts on some bias...



Please give me an opinion and maybe an explanation of the darkening 
other than deposited cathode material. It will be greatly appreciated. 
Thanks in advance for any advices.


<http://www.martakson.se/scratch/rca_6ah6_dark_tubes.jpg>

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