RCA blackplate tubes ... Do the black plates make a difference ?

Interesting link ...

Other variables such as ambient cooling due to airflow, tube orientation and correct biasing in power tubes have a greater influence on the plate temperature than the colour of the plate.

My sentiments exactly, which is why I went the direction I did on my custom chassis, adding clearance and making the bias easier to monitor and control. BTW, none of my "go to" tubes are black plate, although I have several in the collection.


... it’s possible that plate material might have some fundamental effect on the tone. Or perhaps something else in manufacture of black plate tubes affects inter-electrode capacitances, transconductance, plate resistance or leakage – all real measureable effects.

^^^
 THIS

Seems likely that different materials and processes would have different results in what otherwise are electronically identical tubes. HOW a tube dissipates heat is a big factor as well, and glass thickness and formulation, as well as something as simple as the material used in the pins would logically affect performance and longevity.

Black-plate RCA 6CG7s and even the coveted black-plate Tung-Sol 6550s aren't worth the extra money. I don't have bulk experience with them but the ones I overpaid for from from respectable dealers tended, in batch, to be excessively microphonic as compared with the later-issue grey-plates. I would not pay a premium for black plates. Metallurgy underwent a lot of changes, many of them improvements, during the post-War period and not all that is older is better.