Was used in a variety of old German radios, not just car radios. Pretty easy to build a circuit around it. Not sure if it is worth it financially, but it would be an interesting project. Just need to get the right transformer(s).
That tube was used in car radios.It would be fine to use in a small amp for about 3-5 watts output.I can't really see it sounding much different than an EL84 or 6v6 though.