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EM71 Repair

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Forum » In General » EM71 Repair
Lars-G. Lundelin
FIN  Articles: 139
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28.Nov.09 12:50

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Reply  |  You aren't logged in. (Guest)   1 Hi ! Got a heap of old tubes and amongst them the EM71. Unfortunately this tube is physically damaged without vacuum. The tube is obviously almost unused and wonder whether if it would be worth to repair and could it be done at all? The damage is that the glass nipple in the bottom of the tube is broken (missing) and there's a "hole in the bucket". Just asking for the sake of curiosity. Lars-G.


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Moved from board »In General« on 04.Dec.09 12:50 from automatically 
Joe Sousa
Joe Sousa
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11.Dec.09 23:30

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Hello Lars,

Too bad that this rare tube is broken.

Attaching a new glass nipple between the pins would be very difficult without disturbing the pins. Perhaps it could be done with a vacuum grade epoxy.

Then there is the problem of putting a fresh getter in the tube.

The getter is highly reactive metal that is deposited in the interior of the glass and looks mirror-like. It traps the last remaining oxygen atoms after a full vacuum has been done.

When the glass broke, this metal mirror oxidized pretty quickly into a white film.

The closest thing I have seen to what you are asking, was in a video on YouTube, where CRT's were hand made at home.

In this case, getters were not used. The vacuum was adequate to light up the phosphor without internal arcing, but might have been too gassy for amplifier use, causing excessive grid leakage.

I suppose the greatest barrier to seeing this tube lit up again would be getting a new glass nipple between the pins.

I also don't know if the phosphor in the DM71 would have been damaged by now, from exposure to air.



Moved from board »* TALK - visible for members only« on 11.Dec.09 23:30 from Joe Sousa 
Lars-G. Lundelin
FIN  Articles: 139
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12.Dec.09 15:34

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Reply  |  You aren't logged in. (Guest)   3

Thank you Joe for the reply!
I guessed that it would be too tricky to get this EM71 working again because it's likely that the tube also is soiled with dust inside too.
Well, nothing to cry about.

Wishing a Merry Christmas and a Happy New Year!


This article was edited 12.Dec.09 22:09 by Lars-G. Lundelin .