300b lovers

Pindac brings up a good point. Designing a good amplifier is a lot of work, and there’s just as much work getting a product market-ready. The input and output tubes were obvious choices, based on subjective sonics, low distortion, and continuing availability. The challenge was the driver.

Low-powered DHTs have a very small niche market, so have extremely high prices, and it is an open question if they will still be available five or ten years from now. That was a question about the 300B back in the Nineties when the Triode Revival began, but it has been answered ... the 300B has created its own market, and is manufactured in several countries. It has joined the 6V6, 6L6, EL34, EL84, KT66, KT88, and 6550.

The requirement for this amplifier was a wideband driver producing about 2 (or more) watts of very linear Class A power. The first Karna amps used a quartet of hand-matched vintage 45’s. If they were scarce in 2005 when Gary Pimm built the original Mark I Karna’s, hoo boy, they are insanely rare now. Or built only in Germany at frightening prices. Yes, there several Euro-made low-powered DHT’s. All different from each other, with different bias requirements, and some with different pinouts. All very niche products.

The Chinese 2A3’s are interesting. They have single plates, unlike the twin plates of the RCA original, and look a lot like 300B’s with 2.5 volt filaments and somewhat de-rated emission. I’m not quite sure where they fit in the DHT world, but people seem to like them, and demand appears steady.

And then there are the real odd ducks, the Chinese 101D’s. Wow. These are really out there, a tube that hasn’t been in production for ninety years, and extremely scarce in the collectors market, far more so than 45’s. Will they still be produced five or ten years from now? Who knows?

Don and I played it safe. There are zillions of old-stock 6V6’s out there, and a large continuing market for them in guitar amps, much larger than the hifi market. Whichever tubes we selected for this amplifier, and the new preamp, we wanted replacements to be available well into the future, and entertainment value in pawing through old stocks, if the owner wants to do that. All we ask is the pairs be well-matched, both for sonics and optimal performance.

It’s my understanding that KR audio is now manufacturing a 101D tube in the Czech Republic. But yes, in the big picture a relatively rare tube. I use the Psvane W.E.Replica 101D in my preamplifier. It’s very good sounding and fortunately has proven to be very reliable.

Charles

Hello, all.

A big THANK YOU to Don and Lynn for their collaboration in developing these new 300B amps. I'll be at PAF from Thursday through Sunday, and will set aside plenty of listening time in the Spatial Audio/Don Sachs 'experience' room. I must admit to being giddy with excitement in anticipation of how these amps sound with Clayton's speakers.

I'm looking forward to putting faces to names at Pacific Audio Fest. 

Michael 

As Lynn mentioned above, we chose the 6SN7 and the 6V6 because both are in current production and there are very good modern versions of each being built.  Obviously there are lots of 300b choices as well.  I favour the Linlai E-6SN7 beause it sounds wonderful and is reasonably priced.  The JJ 6V6 sounds quite good.   I love the old stock Russian black bottle 6V6 in here and you can still get them for reasonable prices out of Ukraine, Romania, and other places without sending money to Russian vendors at this time.  You do need pairs that are within maybe 2 mV of each other for full bass performance in the amp.  Matched pairs of 300b for the same reason.   They are all readily available, and the amp runs tubes at sane operating points so they will last a long time.   We didn't want to produce an amp that required really expensive tubes that could be unobatinium  in a few years.

It has been well debated 20 years ago during golden years of  direct heated power triodes.

Based on tests on ALTEC/JBL horn systems:

300B is middle of the road of all those small/medium signal direct heated tubes.

It has good/mellow middles, lose/weak lows and not very sweet highs. 300B has longest life among those DH tube.

PX25 has best low end quality among all < 8W tubes.

VT25A/10 has best high end, I built and love the sweet sound.  However, the tube is very fragile, did not last.

if you want to best balanced sound, push/pull 45/50 can give you what you need.

For small signal (pre-amp) tubes, 26 sounds the best, and same time is hardest to build the amp due to sensitive to hum and very low heater voltage.