06-04-2017, 09:35 AM
Back in 2009 HKS started a thread in Paul Stenning's forum:
http://www.vintage-radio.net/forum/showt...hp?t=41149&highlight=work
He comments about the engraving on the envelope "AX33" and AVO VCM163 suggests this might be the expansion coefficient of the glass:
"The 33 in the marking is possibly the borosilicate glass type ("Pyrex"). Often referred to as "33".
3.3 parts per million per degree Kelvin is the low coefficient of expansion for this type."
Having acquired another CRT recently that is of the older blown type rather than that of John's type which has the moulded face plate I was interested to see that it was engraved "AA93".
If AVO VC163's suggestion is correct then perhaps my tube has 9.3 ppm/K.
This might suggest that the earlier blown CRTs are made from soda-lime glass rather than borosilicate glass.
Both early and later CRT types are labeled as PYREX BRAND but reading the wiki it would appear that Corning produced both boro' and soda types under the PYREX label.
https://en.wikipedia.org/wiki/Borosilicate_glass
I am also aware of two other CRTs with engraving. The blown tube in Steve Osler's 702 has "BK90"
and another with the moulded face plate has "AU56".
Assuming that the engravings are expansion signatures then clearly EMI were experimenting with glass properties and perhaps we can say that those with moulded screens are made of borosilicate glass and the earlier ones are of soda-lime glass which might imply that the earlier ones could possibly be reconditioned.
Peter
http://www.vintage-radio.net/forum/showt...hp?t=41149&highlight=work
He comments about the engraving on the envelope "AX33" and AVO VCM163 suggests this might be the expansion coefficient of the glass:
"The 33 in the marking is possibly the borosilicate glass type ("Pyrex"). Often referred to as "33".
3.3 parts per million per degree Kelvin is the low coefficient of expansion for this type."
Having acquired another CRT recently that is of the older blown type rather than that of John's type which has the moulded face plate I was interested to see that it was engraved "AA93".
If AVO VC163's suggestion is correct then perhaps my tube has 9.3 ppm/K.
This might suggest that the earlier blown CRTs are made from soda-lime glass rather than borosilicate glass.
Both early and later CRT types are labeled as PYREX BRAND but reading the wiki it would appear that Corning produced both boro' and soda types under the PYREX label.
https://en.wikipedia.org/wiki/Borosilicate_glass
I am also aware of two other CRTs with engraving. The blown tube in Steve Osler's 702 has "BK90"
and another with the moulded face plate has "AU56".
Assuming that the engravings are expansion signatures then clearly EMI were experimenting with glass properties and perhaps we can say that those with moulded screens are made of borosilicate glass and the earlier ones are of soda-lime glass which might imply that the earlier ones could possibly be reconditioned.
Peter
