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-   -   New GM70 tube with problem (http://www.diyaudio.com/forums/tubes-valves/168487-new-gm70-tube-problem.html)

FullRangeMan 12th June 2010 08:22 PM

New GM70 tube with problem
 
HI,
I receive yesterday a new graphite plate GM70 pair tubes made in 1986-Ulyanov, one tube looks OK, but the other have a loose piece of glass inside!!
Never seen this before and do not know what to expect from this tube. The piece of glass is small, about 2mm large, triangular, like a splinter of glass, and today it is no more loose, it is glued or stuck at the bottom of the tube, near the output leads.
I looked inside the tube with a light and see there is a sticky orange film/skin inside at bottom of the tube where the glass piece is adhered. I carefuly inspection the tube and do not see anything abnormal or broken, the two getter blurs are OK, as new, the tube is new, the socket pins are unused.
Unfortunately I do not have a amp or a tube tester to warm this tube, only a DMM.
Do it is usual have pieces of glass insise a tube?
What I can expect from this tube?
What I can do with a DMM?
I thanks in advance any tip or suggestion,
Gustavo

Palustris 12th June 2010 08:36 PM

I can't speak specifically about the GM70, but from reports here and on other forums it seems as if it is not uncommon for one of these large tubes to have a glass shard in it. Since it is glass it is not in danger of shorting any of the electrodes and further since it appears to be stuck to the bottom of the tube I would guess that it is OK.

FullRangeMan 14th June 2010 03:16 PM

Thanks Palustris for your input, I appreciated it.
Gustavo

radiostar 14th June 2010 03:32 PM

I also think it's ok, I've seen few 211 and GM70s with small glass pieces inside.

If getter is ok, hope it works fine.

kevinkr 14th June 2010 04:28 PM

Should be ok, one thing to also look out for in these tubes is bubbles in the glass (I have one with this issue) as these are likely to fail in use due to thermal stress in the glass. I expect it would make for an exciting couple of moments.

FullRangeMan 15th June 2010 03:43 PM

Thankyou boys for your help so far.
Gustavo

FullRangeMan 16th June 2010 04:24 PM

Quote:

Originally Posted by kevinkr (Post 2216393)
Should be ok, one thing to also look out for in these tubes is bubbles in the glass (I have one with this issue) as these are likely to fail in use due to thermal stress in the glass. I expect it would make for an exciting couple of moments.

Hello Kevin,
Just read your nice site about the SCD-1 mods, and see that your site support the Stereo format and not the Multi-confusion-Channel format, so I wish compliment you for it. The best musical experience is a Stereo tube amp yet. We need new supporters for the Stereo format to grow-up.
Cheers, Gustavo

Miniwatt 17th June 2010 03:13 AM

Quote:

Originally Posted by radiostar (Post 2216340)
I also think it's ok, I've seen few 211 and GM70s with small glass pieces inside.

If getter is ok, hope it works fine.

That's good news. I once dropped a 211, after which I heard a piece of glass rattle inside. I put it aside as I was afraid to use it, I'll blow off the dust and take another look at it. Not that I have a 211 amp..

HollowState 17th June 2010 03:38 AM

Quote:

Originally Posted by Miniwatt (Post 2218887)
That's good news. I once dropped a 211, after which I heard a piece of glass rattle inside. I put it aside as I was afraid to use it, I'll blow off the dust and take another look at it. Not that I have a 211 amp..

Also check the pins at the base with an ohmmeter. Only two diagonal pins should show continuity which are the filaments. And look at the two springs at the very top center. They should be of even height. Of one is loose or very raised, the filament is probably gone.

jlsem 17th June 2010 12:10 PM

The 211 and other similar tubes have glass insulators on the leads attached to the elements of tube. They seem to be made of fairly thin glass and little shards often break off during handling. Not a problem unless you are trying to sell it, because audiophile buyers get freaky about little **** like that.

John


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