300b lovers

I have been an owner of Don Sachs gear since he began, and he modified all my HK Citation gear before he came out with his own creations.  I bought a Willsenton 300b integrated amp and was smitten with the sound of it, inexpensive as it is.  Don told me that he was designing a 300b amp with the legendary Lynn Olson and lo and behold, I got one of his early pair of pre-production mono-blocks recently, driving Spatial Audio M5 Triode Masters.  

Now with a week on the amp, I am eager to say that these 300b amps are simply sensational, creating a sound that brings the musicians right into my listening room with a palpable presence.  They create the most open vidid presentation to the music -- they are neither warm nor cool, just uncannily true to the source of the music.  They replace his excellent Kootai KT88 which I was dubious about being bettered by anything, but these amps are just outstanding.  Don is nearing production of a successor to his highly regard DS2 preamp, which also will have a  unique circuitry to mate with his 300b monos via XLR connections.  Don explained the sonic benefits of this design and it went over my head, but clearly these designs are well though out.. my ears confirm it. 

I have been an audiophile for nearly 50 years having had a boatload of electronics during that time, but I personally have never heard such a realistic presentation to my music as I am hearing with these 300b monos in my system.  300b tubes lend themselves to realistic music reproduction as my Willsenton 300b integrated amps informed me, but Don's 300b amps are in a entirely different realm.  Of course, 300b amps favor efficient speakers so carefully component matching is paramount.

Don is working out a business arrangement to have his electronics built by an American audio firm so they will soon be more widely available to the public.  Don will be attending the Seattle Audio Show in June in the Spatial Audio room where the speakers will be driven by his 300b monos and his preamp, with digital conversion with the outstanding Lampizator Pacific tube DAC.  I will be there to hear what I expect to be an outstanding sonic presentation.  

To allay any questions about the cost of Don's 300b mono, I do not have an answer. 





I belong to the camp that prefers simple triode circuit with interstage coupling in DHT SET. It sounds more dynamic and transparent to my ears.

I don’t think it’s just an implementation issue though. DHT output tubes such as 300B are not that easy to drive and will not sound at its full potential if driver circuit is inadequate. The coupling method affects driver tube’s ability to swing voltage/drive the output tube, hence has direct impact to the final sound.

Interstage coupling allows more voltage swing to be squeezed out from the driver tube in theory and practice. In addition, the output tube can recover from overload very quickly with interstage coupling as the grid current can easily go through secondary winding of the interstage transformer to ground - an unique benefit of interstage transformer. These benefits are not insignificant in DHT SET.

I suspect that interstage coupling is less important for IDHT output tubes since IDHT output tubes are often easier to drive compared with DHT output tubes.

Also, it’s easy for me to advocate for interstage coupling in DHT SET as that’s not difficult to do in DIY - where cost, weight, and space are often less important (in fact, interstage transformers are often cheaper than high-end coupling caps). But if a manufacturer needs to fit everything in a single box, then the choice is very limited.




I used the 6SN7 to drive both KT66/6L6 and KT88 in two different amps and they are great for that.  They are marginal to drive a 300b.  As @atmasphere said, there are many approaches and schools of thought about drivers.  Many paths to audio nirvana as it were.   There are also many power supply approaches.  As for SE vs PP, well, traditional PP has issues with phase splitter circuits right in the middle of them, and SE amps do have certain types of distortion.  These amps do PP a different way and limit the phase split issue and avoid some SE distortion.   Again, there are many fine examples of all sorts of amp topologies, but these don't sound at all like other PP amps you have heard.  They sound like a great SE amp with the drive of a PP amp.  That is the design goal....

@ffzz ​​​​@donsachs 

Thanks for your very informed feedback and perspectives. The builder of my 300b (Israel Blume) Coincident SET mono blocks decided to go with an interstage transformer and 6EM7 driver tube. As has been openly acknowledged, numerous paths to success. In my case I can happily say that the sonic outcome is superb.


RM's minced no words in responding that 6SN7 tubes were a very poor choice of tubes -- "better employed in old TV's", because of their inherent high noise levels.  

@whitestix I encountered that with him as well- although by that time he was beefing about the 6SN7 linearity family of curves. Turned out his source was an early Tung Sol tube date manual that didn't reflect 99% of most production tubes. RCA and Sylvania of course figured things out with the 6SN7 early on and in another year or so, so did Tung Sol. RM had the bad luck to have a Tung Sol manual that was outdated. 

There is a group who prefers this approach and there is a group who prefers the more simple way - using half or the 6SN7 in parallel as one triode and interstage coupled with the next stage, or alternatively using a more capable driver, including a DHT such as 300B itself, 4P1L, 10y, 801, EML’s 20 or 30, etc. 

@ffzz I've found that implementation plays an enormous role in zero feedback amplifiers: grounding, component quality, power supply design and of course getting the operating points right in the circuit design. I challenge the idea that using an interstage transformer is actually a simpler approach- it is once you have a suitable transformer, but a good transformer design is the tricky bit; on that account direct-coupling is IMO easier. It has the same advantage of being able to support class A2 operation as well as instantaneous overload recovery, plus wider bandwidth and lower distortion.

The lower distortion may well be why it sounds less 'dynamic'! The use of that word when associated with SETs is always tricky, since most of the 'dynamic' nature of SETs has to do with how they make distortion. IOW its normal for a lower distortion circuit to sound less 'dynamic'. 

These amps do PP a different way and limit the phase split issue and avoid some SE distortion.   Again, there are many fine examples of all sorts of amp topologies, but these don't sound at all like other PP amps you have heard.  They sound like a great SE amp with the drive of a PP amp.  That is the design goal....

@donsachs +1

I've been harping on this very issue for years. Our amps do not have a dedicated 'phase splitter', relying instead on good CMRR in the differential voltage amplifier.