It is probably a B7A/NEON, NE-45 lamp. Grainger.com lists the lamp, probably others too. Others here may have better information. It has been over 30 years since I had my hands on a TV-7.
Radiodoc
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:I broke the neon bulb that does the shorts test on my military TV-7U tube tester. I need to replace it before I test tubes, but I don't know what to ask for. It has a screw socket and measures about 1/2" diam. and about 1.6 inches long. Can anyone tell me what to buy and where? Dick