I am getting the kinks out of my old Crosley 547 "Fiver," slowly but surely. After I modified the chassis grounds to the filter caps it no longer hums as badly, but the 6K6 G tube is flickering blue in the top (which it did before I messed with it.) It looks like a summer thundercloud with some lightning in it. When it flashes blue-purple the radio makes static and when it plays, it is not very clear--sounds relentlessly "vintage," not what I like. I know it's not a hi-fi but surely they weren't that bad back then.

Incidentally this tube gets very hot on top--you can't touch it, unless you have giant gloves on or really want a second-degree burn. The rectifier tube, a 5Y3, does not get as hot as the 6K6 G, even though rectifiers usually get very warm indeed.

Has this tube blown out?

Gassy tube, keep messin' with it and you'll likely be replacing output transformer as well.

Sounds like the tube us gassy.
Output tubes usually get hotter. The data sheet shows over 9W for normal use

Thanks, guys.

I substituted a 6G6G from another radio temporarily and played it without the weird sound. Now I've got to get a proper 6K6 and put it back to stock. Other than the three Flexohm resistors I think the radio is just about fixed up.