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"Matching" of dual triode tubes - how close?

I'd like to understand how matching affects the sound & performance of dual triodes. 6SN7s are of particular interest, but I suppose it could apply to any dual triode. There are several aspects to this question - probably closely related, but maybe not:
1. If a tube is not closely matched - let's say for the sake of discussion that the two triodes are within about 20% of each other, under what conditions will the difference be audible? How will it impact the sound? Frequency response? Extension at the extremes? Imaging? Noise?2. In an exchange of messages on a different forum someone told me that the tube matching wouldn't really make a difference - that is, the tubes he was selling were "close enough for all practical purposes". Is this just an attempt to pass off poorly matched tubes? Or is it true?Thanks,Markus
128x128markusthenaimnut
armstrod
613 posts
 
The 6SN7 is my favorite tube, and I've used them extensively in at least 3 different preamps. My experience is matching within 20% is more than enough, but here's something else to consider: some (maybe many?) preamps only use 1 of the 2 triodes for each channel. This true for my current Modwright LS100, confirmed by Dan Wright, who said you could use tubes until they were below nominal for one triode and then swap them and use the other triode. In that case, it wouldn't matter that the triodes in the same tube matched, only that triode 1 of one tube and triode 2 of the other matched, and vice versa.

So the takeaway is I mostly agree with millercarbon. Buy tubes that are close and don't sweat it. And if you buy tubes from private parties, invest in a tube tester. I'm glad I did.
tomcy6's avatar
tomcy6
2,590 posts
 
6SN7s are dual triode small signal (preamp) tubes. My reply and the information from the Upscale Audio webpage applies to 6SN7s used in a preamp.
tomcy6's avatar
tomcy6
2,590 posts
 
markus, you should send atmasphere an email.  He builds amps and likes the 6SN7 tube.  I'm sure he could tell you whatever you wanted to know about it.  He posts in the forums here pretty regularly.  If you do correspond with him, please post what you learn here.
kalali's avatar
kalali
1,977 posts
 
There are actually two questions; balanced triodes in a single tube and balanced tubes, and the need for either in a preamp depends on how and where they are used in the circuit.  
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