[Jeffhs]

That 3CU3 is the first HV rectifier tube I have ever seen with damage like yours had. When you said the tube was "in half", I immediately looked at the attachment and, sure enough, saw the tube's glass envelope literally broken in half. I wonder what caused that type of damage, although my best guess is the tube was severely overloaded somehow. Whatever it was, the overload must have been severe enough, and then some, to cause the tube to come close to exploding. In fact, I am surprised the tube's envelope did not shatter, rather than splitting in two as it did.

It could also be, as MadMan said in his post, that the tube had a manufacturing defect and just broke open. If the TV now works as normal, with normal HV, I wouldn't give it a second thought.

BTW, 1968 was about the time everyone was beginning to worry about X-rays from color televisions. I mention this because of the warning on the base of the broken 3CU3 regarding the possibility of the tube emitting high, even harmful levels of X-rays if the tube was not properly shielded. This problem was addressed and apparently corrected, however, by about the mid-'70s (my best estimate), which should have set the collective public's minds at ease. Of course, this (X-ray radiation) cannot occur with today's flat screen televisions since there are no tubes in these sets, and the voltages found in such TVs are nowhere near the kilovolt range.

Also, I can now understand why, in the late '60s-'70s during the X-ray scare, parents often told their children not to sit too close to the TV screen since, as I said above, there was a potential X-ray hazard with color sets of that era. Even today, with flat screens, kids are being warned not to sit too close to the set because of the possibility (even the likelihood) of eyestrain.