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Old 03-02-2015, 01:16 PM
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ppppenguin ppppenguin is offline
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Join Date: Oct 2009
Location: London, UK
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Final anode (ultor) seal problems with Pyrex

There have been several reports of problems with the glass/metal seal for the fnal anode (ultor) connection in Pyrex CRTs. The EMI 6/6 that I had rebuilt in 1987 didn't have any problems here. Though there may be a long term problem which we haven't seen. For some years the set hasn't been readily accessible as it's in the stores of the National Media Museum, Bradford UK.

A recent correspondence with Darryl hock set me thinking. Why have recent attempts at Pyrex rebuild had problems with the final anode connection? An unusual aspect of the 1987 rebuild was that the CRT was pumped cold. 2 reasons:

1: The oven wasn't big enough
2: The guys doing the rebuild felt there was too much risk of implosion if the CRT was baked in the normal way.

I don't know if a HF heating coil was used to outgas the electrode assembly. I assume it was.

Of course this anecdote doesn't amount to evidence but it might just be important. Cold pumping has its risks, mainly from gas molecules adhering to the Pyrex and wrecking the vacuum. I know that oversize getters were fitted because of this risk.
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