What happened to the Directly Heated Triode preamps you were building ?
Yes I built DHT preamps for quite a long time , I built the first commercially available 300B preamp, and built quite a few different models, using different DHT tubes over the years. 45, PX4, 33, 101D, 4P1L and a bunch of obscure tubes.
I still very much like the lush, slightly warmer sound of DHT , and I still have a DHT preamp in one of my systems.
In the right system, or to cater to a certain subjective taste they can be very enjoyable, and I will still custom build them if required.
Its a bit of a shame that the best DHT preamp tubes are NOS from the 1930-50 period, I really like the 71A, 10/10Y/801A , but buying them now is a bit of a lottery as to what you will get.
And DHT tubes, because the filament is in the signal path, are usually very microphonic. Some are worse than others, the 300B isn't too bad , the 4P1L can be quite "ringy".
It doesn't particulary worry me, I even think a little microphonics can be a good thing, but it drives most audiophiles crazy, as they think that something is "wrong" with the tube.
All the time I was building DHT tubes , around 10+ years, I still had 6SN7 preamps, and continued to work on them .
The octal 6SN7 tube was designed for applications such as preamps, and is maybe the ultimate preamp tube.
Everyone uses 12AX7,12AU7, 12AT7 etc, but these tubes were designed for TV purposes and to my ears aren't a patch on the 6SN7 and its Russian equivalent the 6H8C.
The 6SN7, in the right circuit, which lowers the output impedance to an optimum level , without any side effect degradation , is just about perfect in every way.
Its accurate, has a big soundstage and sounds natural and full of ease. Clean solid bass and lots of air.
Most other tubes sound closed in, strained and brittle in comparism.
A couple of years ago I found a combination of componentry and circuit which gave the 6SN7 preamp a performance that I thought gave all the advantages of DHT without any disadvantages.
Its since been fine-tuned and is my number 1 product .
Tomorrow I'll talk about different 6SN7 tubes and the pitfalls and advantages of NOS.
