Hey, that's great news Dave!
That "VTX-X101" tube was Alpha-RF's "house brand" tube, and (as you discovered) they were supplied by Penta Labs. It is essentially a 3CX1500A7 copy. That date code would indicate a manufacture year of 2010 (13 years old), and it may have a lot of running-hours on it...(?)
Now you just need to start looking for another back-up tube... :-)
73,
~Alan
W5ARM
Alan - W5ARM