Yup, I operate ham radio too, but SWL is enjoyable activity at times, especially when the HF ham band condition is poor.
I like my R820, but it does not cover all bands. It has gaps in the freq. it covers. So having some other receiver with full HF coverage is good.
My GR-78's ni-cad had died long time ago, so it had been pulled out and discarded, and I am running it with external 12V battery. Any DC voltage 9V - 12V seem works OK.
The audio of the GR-78 gets raspy at times, but I found the GR-78 very fun to listen to. It has that classic vintage audio, and also it is very quiet and sensitive. I did comparison side by side with other more modern and higher grade rigs, and this GR-78 was as good as them, sometimes even better than them in copying weak signals.
I didn't expect such performance from this humble GR-78 when took out after long storage, but pleasantly surprised, hence made a few videos.
73 de Al.