Hi Lynn,
Reading your previous post encouraged me to order a power transformer and a pair of 15H chokes for input and driver tube. It will give me not just PS separation but also reduces the load current to the 5u4g rectifier that I use for all tubes in this stereo amplifier (180mA total). It also gives me a freedom to increase drivers idle current and probably I will try 6v6 instead of 6f6. 6v6 needs more current.
Now I use very big capacitors for B+ - 2000uf for 300B and 1000uf for drivers. What is the advantage of separate power supply for drivers over big capacitors? How do behave big capacitors during the clipping of 300B?
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.
- ...
- 885 posts total
@alexberger Consider using the tube rectifier for the front half of the amp and good diodes for the 300b. Do a C-L-C for each and use a good film cap as the last one after the choke. Separate power supplies allow the input and driver tubes to basically not know the 300b is clipping. When you push the 300b the power supply for the whole amp sags a bit. With separate supplies the input and driver sections are isolated from the 300b. You will hear a certain ease and clarity to the sound that you don't have now. The Blackbird uses a similar approach, but much more sophisticated power supplies, which I will not get into. |
I second what Don just said. Isolation is the key. You can get away with a power transformer that has dual isolated secondaries, but this is a specialty item so don’t bother tracking it down. At the DIY level, just get another B+ transformer that runs at a voltage suitable for the IT-connected driver tube, and take it from there. In terms of rectifiers, damper diodes are the quietest of all, but they consume a lot of heater current at 6.3 volts. The dual power supply approach is surprisingly rare in consumer equipment, even at extremely high price levels. It is the single biggest improvement you can make to any tube gear, from push-pull 6L6, EL34, and KT88 to SET amplifiers of any type. Extremely large banks of electrolytics are popular over in transistor land, but they are frankly mediocre sounding caps, compared to good film caps of more moderate values from 50 to 200 uF. In the Karna, I used banks of industrial-type motor-run caps from ASC and GE. These are precision parts designed for extremely severe duty outdoors. I prefer them to audiophile parts in that application. A minor audiophile tweak is to bypass the industrial array with a single 0.1uF cap of very high quality, such as copper foil. (Also use copper foil for the RC or LC coupling of the 6SN7, but be aware that wax caps are not suitable for under-chassis use.) Location is important. Keep the wiring, especially in the cathode circuit, as short as possible. This is more important than the type of wiring, although if you want to go nuts, use industrial Litz wire for the critical audio path. Litz does require a solder pot to get rid of the enamel coating, a minor annoyance when working with it. A close second choice is tinned stranded, which is super easy to work with. This approach, if done right, will take your SET performance to the mid to upper tier of Audio Note, in the $20,000 to $50,000 price range. |
Here’s a picture of Gary Dahl (seated) and Gary Pimm, shortly after Gary delivered the newly built Karna amps to our living room in Silverdale, Washington. 2003. Gary Pimm and Gary Dahl look under the chassis Ariel speakers and Karna amps in Silverdale, 2003 The dual B+ power supply chassis is external, connected by the aviation-grade Amphenol connectors at the rear of the chassis. The glowing VR tubes are at the front of the chassis. The EL34 on the left side is part of the high voltage current source that feeds the VR tubes. The audio tubes are 5687 input, 45 drivers, and 300B power tubes. Interstage transformers are under the chassis. This picture gives an idea of what Don accomplished over the past year, reducing this behemoth four-chassis prototype to something that could be practically built, and then exhibited at the Pacific Audio Festival. |
The very first one, the Amity, designed by yours truly, and built by Matt Kamna on an open breadboard-style chassis. Matt has since gone on to co-found Whammerdyne, a company that makes 2A3-based SET amplifiers, and exhibited in the Songer Audio room at the PAF show this year. Amity at night, 1996, Aloha, Oregon We’ve gone a long way since then! |
- 885 posts total