http://www.tubemaze.info/tubes-black-gray-plates/

The CCa Valve uses a standard grey anode (plate) where the GE 5670 uses a carbonized nickel 'black plate' anode.

The black anode structure is a carbon layer over the nickel of the anode. The grey anode structure goes back to the German WW2 war effort, when nickel anodes were phased out for a steel/aluminium compound creating the 'grey plate.'

There are very real benefits in performance for 'black plate' Valves over the common later 'grey plate,' but the process is more elaborate and more expensive. So by the 1960's 'black plate' Valves had become rare as rocking horse droppings and were generally reserved for defense applications where budget is not an issue and not for general radio/communication/consumer use where the pennies are always counted.

So the CCa has a grey anode structure, with gold gridwire and gold-plated pins.

The GE5670 has a black anode structure with gold gridwire and the pins are plain.

Electrically the two are rather close, though the GE5670 has a slightly higher transconductance and slightly higher gain at any given operating point, which often (but not always) translates into a sound that gives more subjective dynamics and more detail.

Nowadays where a Valve is in the market as both 'black plate' and 'grey plate' type, the black plate version is almost invariably rated higher for sound quality than the grey plate version and commands a hefty price premium. Just check out the typical prices at places like Tube Store et al.

Sorry to sound all nerdy but our AMR roots means we are rather fanatical about all things audio and Valves/Tubes are no exception.