When Does Triode Matching Matter?

[BrassTeacher]

I sincerely hope I'm not opening a can of worms here, but when does triode matching matter?
Let me get this one out of the way - Say you have 2 channels, I firmly believe V1 in the left channel should match V1 in the right channel. Not only that, but every corresponding component in one channel to the next. So, we can skip that one. I'm talking about triodes in the same channel.

Now, I imagine both triodes in a differential pair should be matched, it's only logical. The amp I'm about to work on has this for a driver stage, driving a set of power MOSFETs:



For those curious, it's a 6DJ8, but that doesn't matter for this discussion. What matters is that they are paralleled. I'm thinking both triodes should match for best results, but does it matter? Also, matched for Gm, and/or plate current, and/or cutoff point? In some applications, it's better to match transistors for Hfe (current gain), and others matching Vbe (turn-on basically).

Or, does triode matching anywhere really just not matter? (I'll still match one channel to the other, no matter what anyone says!

 

[zackthedog]

Well, if you're using one dual-triode tube for a long-tailed phase splitter or a differential driver stage, matching the two halves would produce better results--equal voltage output and lower distortion. So in some cases, yes, matching can be important. For parallel operation it would seem like a good idea, though perhaps not as critical, except in the case of power tubes.

 

[Mdpaudio]

If you are using a single tube as input and driver it’s more important to have the sections match between channels than in a single tube. That way input sections match between channels and so do the driver sections. If you are using a single tube for the input stage of two channels they should match within that tube. That way the two channels are matched.

 

[peterh]

Yes, in this case and in LTP phase splitters matched trodes ( aka balanced) matters.
Some vendors ( like me actually scans incoming batches for equal triodes for this reason.