Tube question - specifically regarding crackling and humming

[Loquah]

I recently picked up a matched pair of RCA 6DN7 tubes for my S.E.X., but have found that with them installed there is a faint hum in the left channel and some faint, intermittent crackling in the right channel. The amp is completely silent with my 2 other sets of tubes.

So I'm wondering if either or both of these symptoms should subside with some use and or pin cleaning. Are these lack of use symptoms (the tubes have been sitting in storage for a long time) or do they suggest more permanent problems?

[mcandmar]

In my experience this is a very common issue with 6DN7 tubes, they will either sort themselves out with a few hours use or they will never recover, its a bit of a lottery.

If they don't quieten down its also worth looking into the heater centering mod with two 100ohm resistors as it may make them totally silent and usable, i dont know why but some tubes seem very sensitive to that.

What are they, coin base, black plates?

[Loquah]

Not sure, but not coin base - my coin base RCAs sound great! I'll attach a photo of the tubes in question.

[mcandmar]

Half black RCA's, not seen any with yellow labeling, i wonder how old they are?    I'd let them cook for a while and see what happens..

[Loquah]

The labels are actually red - I think that colour is a result of the flash reflecting off the bronze chassis plate