I don't know anything about the specific tubes that you ask about but I know that the EF91 has a blueish looking band, you can read more about it here: http://www.r-type.org/addtext/add102.htm
/Martin On Saturday, 16 January 2016 13:04:33 UTC+1, marta_kson 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> > > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/2e26c542-e22f-412b-9650-0bc84dbd62ad%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
