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26 vs 27

I prefer the 26 to the 27. Both are highly microphonic, but IMHO the 26 tends to sound better in similar circuits. The 27 seems to have some issues with breakdown of the cathode to filament insulation. I've never heard a really bad sounding 26, but have heard a few NOS 27s that I would not live with for a moment - some sort of linearity issue that resulted in very hard and glassy sound.

I am listening to a signal chain right at this moment that includes 26s..


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Could you give me some explanation as for why there's such a difference between DHT and IDHT?

Are you talking in general or in the specific case of the 26 vs. 27? In general I don't think you can make that case. In the particular case of the 26 and the 27 the 26 represents relatively late evolution of small signal DHTs, whereas the 27 represents the very first IDHT released in the American market.

I'm not sure there is a good answer, and I am not going to attempt to answer your question as I am pretty agnostic on the issue.

OK: Challenge of getting it to work, and cool factor/fashion statement. (Sometimes OK IMHO.)

The biggest problem with these early tubes whether DHT or IDHT is that the techniques used to make them also lead in many cases to severe microphonics, most later IDHT are much better in this respect. Make no mistake the 26 will sing along (and not so nicely) with the music if given an opportunity to do so, and that also applies to most samples of the 27 I have worked with.

I like the 26, I also like the 6SN7A, the 5842/417A, and triode connected D3A, and C3G.. I think of each as being suited to certain types of tasks.. The 26 is a great microphone, err moderate MU triode.. :D Each of the others is suited to tasks requiring progressively more gain and in the case of the 5842, D3A or C3G gain/low rp/and appreciable power capability.

IDHTs are easier to use and some of the early 5 pin and octal triodes (56/76/6C5/6J5/6SN7) in the low - medium mu range also have excellent linearity and relatively low rp's. I like the challenge of designing with difficult tubes which is why 10yrs ago I designed my first iteration of a transformer coupled 26 line stage. I knew the linearity would be OK, didn't know if I could tame the other issues. I still use that much reworked line stage today, its flaws are significant, but overall I prefer it to anything else I have done.

I know I haven't answered the question, but from my perspective this is a question without an answer.