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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. 

 

 

whitestix
kmtang's avatar
kmtang
2 posts
 

I have tried two types of LinLai 300B tubes for some time with shunt regulator at the cathode, i.e., fixed voltage at cathode. I biased it 70mA with 420V B+. The anode-cathode voltage is approx 350V. 

Once the 300B tube got warmed up for about 30mins, the idle current start drifting higher. I had to reduce the idle current to 60mA which will be stable over long operating time. 

The same happens to the EH and the Russian Gold Lion 300B tubes as well. I don't have the WE ones for testing. With use of RC cathode bias won't have such issue but we need to watch out when using fixed bias.

Johnny

atmasphere's avatar
atmasphere
11,640 posts
 

With use of RC cathode bias won't have such issue but we need to watch out when using fixed bias.

@kmtang When setting the bias for any fixed bias amplifier, its good practice to check the bias after an hour of operation. IOW all power tubes regardless of type will see higher bias current over time as the tube warms up. So usually after the amp has been on for about a minute or so you set the bias to about 85-90% of the bias current spec. That way it has less of a chance of damaging the tube as the tube heats.

lynn_olson's avatar
lynn_olson
276 posts
 

Some fixed-bias amps have a separate servo circuit that monitors the bias of each tube, so user does not need to adjust the amplifier. This servo circuit needs to be very reliable, though, since a failure would destroy the output tubes, and possibly damage the bias circuit, as well.

Cathode bias, which is nothing more than a power resistor bypassed by a (very) high quality capacitor, acts like local feedback at DC, and more like fixed bias at audio frequencies. It is not suitable for Class AB amplifiers, though, since the total current going through the pair (or more) of output tubes varies with the power delivery (the efficiency actually goes up as output power increases). By contrast, Class A operation has more or less constant current draw from the output pair, but it is significantly less efficient than Class AB.

lynn_olson's avatar
lynn_olson
276 posts
 

By the way, the traditional definition of "efficiency" is: (Max RMS output power at stated distortion level) / (Total power going into the plate circuit). Power consumed by heaters, filaments, input and driver tubes, or regulators is not usually considered.

For a pair of output tubes ... 6V6, EL84, 6L6, EL34, KT88, 6550, 2A3, 300B, 845, or similar ... they can be set up to run in either Class AB, or Class A. Class AB operation typically has a higher B+ voltage and a lower quiescent (steady-state) current, while Class A operation has a lower B+ voltage and a higher quiescent current. For the same average power draw, Class A usually puts out half to one-third the output power of Class AB, which is why it is less common than Class AB.

Most customers want more power if they have a choice. That was true in the Fifties and it is still true today ... partly because most loudspeakers are very inefficient (less than 1%) and need all the power they can get.

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