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I recently reviewed the Mhdt Pagoda tube DAC. Owner was kind enough to send me three other tubes to test with it. Here are the set of tubes I received:
View attachment 168967
Let's start again with the tube supplied with the unit (GE 5670)
View attachment 168968
Now let's switch to Tesla 6CC42 (GA):
View attachment 168969
Other than slightly more mains hum at 60 Hz, I see no other difference. Gain is reduced negligible amount.
Next up is the Western Electric JW2C51:
View attachment 168970
Distortion is 0.7 dB lower. So nothing significant there.
Finally I tested the Western Electric 396A tube which produced a surprising result:
View attachment 168971
Channel 1 is the same but channel 2 has 6 dB lower distortion. Is half the tube better or is there some asymmetry in the design?
That's all I have for you.
Conclusions
It is clear that by far the source of distortion is the design and not choice of tube. In three cases the difference is negligible and inaudible. In the forth example, the WE 396A, there is reduction of distortion in one channel. In the larger picture, there is so much distortion here that reducing it with this tube is not going to make a difference one way or the other.
Notice the level of instrumentation it takes to see the impact of the tube. You need to measure to see if there is a difference and not just assume there is.
Personally even if I signed up for a tube product, I would not waste time "rolling tubes." You are likely to suffer more from "rolling placebo" by your brain than any variation in such tubes.
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Thanks for this, and I’ve suspected it for quite awhile. I’ll tell you that there is a strong placebo effect, plus if you listen to enough people they’ll tell you everything from 1957 XXX tube to 1958 of the same tube sound different because they’re a year apart. Personally I think the differences that people believe they hear come from mismatched tubes, or different gains from different manufacturers possibly.
That being said, I just picked up a Freya + and I quickly swapped in a brand new NOS set of Sylvania‘s from back in the day. I have a good tube supplier/friend so I know what I’m getting.
How do they sound? probably just like the ones I pulled out…. but that placebo effect is strong indeed. I swear it sounds twice as good LOL.