I have 2 of those....very used though......in fact only one since I took apart one...it actually uses the same ballast as a regular PL 13 watt one!!! And the date is June 2004! Those aren't that old...but based on older design....That's what Dave told me! Note the GE logo is a after 1989 design!
You won't be able to "stick" a PL in...but you can take ballast out and reuse it on PL 13 watt......but let me tell you...when you take ballast out....the inside plastic may be brittle like mine.......
Hmm, I believe the OCV isn't high enough for two PL7s in series to strike and there isn't enough space for a second ballast. Maybe just the tube from a PL 13 quad will fit.
Awesome lamps these are....like the Philips *SL's and the PL13 adapters, it's always worth stocking up if you find them. I bought a whole case off eBay a while ago...I have two lamps in nightly use and a third used occasionally and I probably should put a few in my will since they'll outlive me.
Mine is at General Electric Standard Compact Fluorescent Bulb