Go find TOKIN THF-51S on ebay, same devices in the FIRSTWATT SIT-4, Nelson has several circuits he showed at Burning Amp Festival. Zen Mod has a very fine kit called the Singing Bush (I built that one).
You can still find VFET's and even SemiSouth JFET's for sale by members in the Swap Meet section. It is affordable, and not hopelessly expensive to find the devices and build a great amp, it will take time to collect everything.
When you compare this to a good pair of 300B tubes, it's a bargain.
The realities of semiconductor manufacturing are that anything used in audio is always going to be a secondary or tertiary application of the particular fab process.
If in the heyday of audio (the early-mid 80s) there wasn’t enough demand to continue Vfet production, and there is no application for power Jfets/Vfet in today’s market that could make it worthwhile for a fab to produce and market them, and class-A jfet audio by itself isn’t anywhere near big enough to stroke that demand.
Yes, I agree that there is a demand for Class-A amplifiers. They are great, if you don't have one you really should build one, it’s great fun and makes a wonderful amp. Commercially however, none of the Pass Labs amplifier, nor any of the competition use Vfet/Sit devices, only the Firstwatt SIT-* amps.
The new SIT-4 is probably going to be priced around the $5000 mark, which certianly isn’t chump change, it is nowhere near the $14,000 figure mentioned. (And for that matter the Pass Labs XA25 is about the same price. Of course, there are moe expensive amps in the lineup)
SO… Source some devices, and build an amp. It will cost a pittance compared to anything commercially available and you will be stunned at the fantastic sound.
🙂
Tokin SITs are still available for purchase. They are not $2 or $5 mosfets but then the SITs are more akin to triodes than mosfets, and people readily pay hundreds of dollars for a triode. So a $100 or $150 Tokin SIT such as a THF-51S is still a good deal. A 50W single ended SIT amplifier can be built with it, at much lower cost than a single ended triode amplifier. And it will sound great. And the SIT will not deteriorate with use, unlike a triode.
You can get supremely excellent sound from class-A biased amplifiers that do not contain a single VFET or SIT or triode. Just plain old MOSFETs and plain old bipolar transistors. And huge heatsinks and heavy bias currents and shrewd circuit design.
There are quite a few examples here on the Forums and in the diyAudio Store.
There are quite a few examples here on the Forums and in the diyAudio Store.
Both Ben Mah and Mark Johnson have threads with excellent circuits which they designed as described above, in the Pass Labs forum. I've built power supplies, power supply filters, and front end circuits of his. Ben Mah has helped members diagnose and fix their mistakes on preamps, power supplies and amplifiers. 6L6 is the definitive voice for Nelson Pass designed Class A amps, preamps, power supplies building instructions, I've built several using his build instructions.
They provide excellent and valuable advise to all, you would be wise to listen to them and explore their suggestions.
They provide excellent and valuable advise to all, you would be wise to listen to them and explore their suggestions.