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Re: Help this pathetic newbie to tubes : )

Posted by Jim McShane (D) on August 6, 2006 at 12:27:14

In Reply to: Re: Help this pathetic newbie to tubes : ) posted by Mechans on August 5, 2006 at 19:37:01:

"I have bought so many tubes from dealers with good reputations claiming NOS but the tubes show some sign of being used some have obvious pin wear or look a litlle cooked"

Okay, how would someone suggest I test the tubes without inserting them in a tube socket (I did see your acknowledgement of this in your post)? Did you know the tubes were also inserted in the socket at the factory - at at the factory the tube is heated to the point where the plates GLOW BRIGHT RED? Did you know that MANY tubes got significant burn in at the factory?

Do you know that most of the NOS tubes I get now have corrosion on the pins? That corrosion has to be removed, usually by mechanical means. The evidence of the removal efforts is clearly visible on the pins, as I often use a soft brass bristle brush. And crooked pins are straightened by me, which also leaves visible marks on the pins.

Do you know that NOS JAN Philips/Sylvania tubes often have a brownish deposit that extends from the tube base to about 1/4" down the pin? I know the tubes in question are new unused too, because I unsealed the cases.

"And no I am sorry but every brand new tube has has perfect getteering not brown or black no matter this nonsense of gasses being burned off discoloring the."

I'm sorry, but you are dead wrong. Black gettering is actually superior in performance to silver, and it has to do with the getter flashing process at the factory. MANY small signal tubes have a small area of brownish/blackish discoloration in the getter flash right from the factory, and it's usually a very consistent shape and size. It's hard to imagine that consistency occurrring simply from use. The GE small signal tubes probably show this more than others. Clear top 6SN7 family tubes often show very small deposits or darkening on the tube glass above the internal structures. Those often are from the factory, as it takes only a few miuntes of burn in or testing before they appear. I know, because I've done some experiments to determine how long it takes for those markings to form (I see silver deposits about the 1/2 size of the top of a golf tee in one hour's running time). Don't believe me? Fair enough; look up Eric Barbour's article about the 12SX7 in Vacuum Tube Valley issue #8 for more info.

Eric states:

"New-in-the-box 12SX7s are often discarded as 'useless' because there are foolish people..." (snip discussion about heater voltage not relevant to this post). Continuing, he goes on to say "Another reason for discarding them is visual inspection; most 12SX7s were heavily burned in before shipment (my emphasis), resulting in shiny 'getter spots' on their tops, directly over the cathode ends. This is also seen in some old 6SN7s, 6SL7s, 6J5GTs, and other tubes."

Eric continues - "It is often assumed by the ignorant that these spots indicate an old used tube that will test weak. It is an amusing trick you can play on radio collectors, in order to coerce them into parting with their fine NOS 12SX7s (again, my emphasis) at a low cost."

Eric is not Mr. Tact & Diplomacy by any means - but he knows tubes!

I just wanted to address certain statements in your post, that's why the long answer.

IMHO tube newbies need to remember the old saying - "a little knowledge is dangerous"! Despite all the years of my work with tubes I still have SO much to learn - when I read a post by Jimmy or Poinz or Eli or some of the other guys here I feel so DUMB!! Talking to Uncle Ned makes me feel so inadequate, he has so much experience and knowledge he's happy to share! So as a newbie, try to avoid taking stands - immovable, unalterable, non-negotiable absolutist statements are hard to live with if you aren't correct. Crow is NOT a tasty bird!

Take positions instead - fluid, flexible, and open-minded - and you'll gain respect and credibilty with the Jimmys, Elis, and Erics (Poinzs) of the world. And you'll find that same group of real experts much more willing to help when you need it!

End of sermon... gets down from soap box...

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