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Follow-up on my matching tube post below

Posted by JoshT (A) on June 30, 2017 at 16:02:34

Thanks for all the input on my question below about tube origin and matching.

I have finally been able to open up the Rogue RP-5 preamp and remove the tubes for inspection, and here is what I found.

Here is a picture of one pair.
One tube says Mullard, Made in [hard to read but looks like Great Britain] and has the following etched numbers on the bottom: K6 B8E
The other tube says Amperex [with Bugle boy emblem] 930, Made in Great Britain, with etched number on the bottom: K6 B8K

Here is a picture of the other pair.
One tube says Heath, Mullard, [country of origin wiped off], has etched side numbers 845 1022
and etched bottom numbers B8E (nothing else noticeable)
The other tube says Mullard, Made in Great Brittain, has etched side numbers 841 1022 and etched bottom numbers K6 B8C.

I have been unable to decode the etched numbers based on the guide inmate Sondek kindly provided, but given the fact that the construction of each looks identical to me and that they all appear to have similar codes and are all made in GB, I assume it would be reasonable to assume they are both matched pairs as represented by the seller and that no mistake was made in putting them together.

I would be interested in any comments on these tubes. They sound great to me, except I think I might be hearing some microphonics from one channel (a slight ringing sound following higher note piano strikes), though I'm going to check on another system. Also, unfortunately, I am getting some static sound occasionally through the headphone amp, which may or may not be tube related (Rogue said it could be an opamp instead). I have checked the headphones on my Oppo and they are fine, so it's in the headphone circuit. So, I have the stock JJ tubes in now and will see if the static continues with the headphones.
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