1978 Celestion Blackback G12H, T1217, 30watt, 16ohm, 75Hz

1977 Celestion G12H Blackback, T1217, 30w ,75hz, 1777 Cone
I know little about speakers but I understand this to be a useful speaker for those interested in vintage tones. It's out of a Carlbro Stingray amp (it looks like it was a replacement speaker for that amp). I tested it in the amp and it sounded crystal clear.  The dust cap is slightly dented but I understand that can pulled out with a vacuum cleaner. There appears to be staining on the cone (though it's perfectly intact). It had been in storage in a bedroom wardrobe for 25 years though.

From what research I was able to do on this I note that this model speaker doesn't seem to be common with the 75hz. Happy to supply more pics if need be. Also, I have a multimeter but haven't a clue how to use it. If you're will to direct me I can acquire that info too.

Note: There appears the a rise on the edge of the dust cover. It's hard to touch. I think it's hardened glue. I photographed this as best I can.