300 B SE Monobloc Audio Amplifier by Bluebird Audio
The Blueberry Amp 3 1/2 watts per channel, < .03 % distortion which uses 60 year old triode tubes from RCA, Sylvania, and others. Price for assembled and tested amp=$1270,
The "Theater Amp" with the hallowed and revered , large 300 B Triode tube from the 40's, producing 8 watts per channel. Separate Power Supply for each channel = "Monobloc"
Price for the Blueberry = $1270 - shipping to the contiguous 48 states at 30 pounds will be approx $48
Price for the Theater Amp=$3700- shpping will be costly. large as a picnic cooler, and weighs about 90 pounds
Some notes on the electronics involved in Blueberry
The row of LED's are designed to fire at each doubling of wattage from.006 watts up to 7 watts. It is interesting to watch as your music goes from soft passage to awesome grandness of scale. Tube amps are visually pleasing, owing to the warmth of both the music and the glow from the hot filaments...and the dancing LED's. One builder of solid state amps quipped, with a sneer, that "Dogs are likely to mistake a tube amp for a fireplace and lie down in front of them".
Some inportant notes on the 300 B Theater Amp
The smaller amp on the left here, the "Blueberry" amp was a deliberate effort to make a super high quality amp at the lowest price possible. And it is good enough to compare favorably with the "Theater Amp". The Blueberry took two years to perfect. Although one fifth of the price of theater amp, it is one sweet and loud amp."A/B" tests reveals that the Blueberry sounds as good as the big Theater amp at 2 watts per channel. Of course the Big Theater amp is twice as powerful=capable of 8 WPC The thing that makes both of these amps so wonderfully musical is that they both employ the hallowed triode vacuum tube.Tubes were made smaller, with more elements to increase wattage -such as the "pentode" or five element tube - but the big juicy triode happens to have been the best for sound, voice or instrument...and has never been surpassed in grandness of sound.
Both these amps bring new meaning to the term "Glorious Sounding". They each employ the simple TriodeVacuum Tube. The 300 B tubes do exhibit the lofty, poetic terms you often hear written and said about the 300B. Terms like "airy", "transparency", "Immediacy""front row at the live orchestra immediacy"... many of these terms can be considered to refer to a more accurate , or more "real" sound of , say, a cello, guitar, horn, voice...chill bump real...in the room with you real.
Thus the cost is justified ~ many audiophiles believe. I can tell you I enjoy this amp so much, that it will probably feel a little like one's lover suddenly leaving you for another. On the other hand...one can get used to the next new love, can't one? We humans can roll with the punch. Meaning, we can grow fond of any good lover..which Single Ended Triode amps are...they are all good. As one wag once said, "The worst I ever had was wonderful "..SE Amps are exactly like that.
The image below is of a precision instrument by Hewlett Packard, especially useful in the audio industry.These instruments were very costly back when government and industry required precise measurements. Observe the "scale" is on"10", that is to say, 10 voltsAC on the top scale. Disregard the knob with the center arrow. The meter is reading 4 VAC.
To determine the wattage, you "square" this 4 VAC, = 16. You then divide this number by the impedance/ohm rating of your speaker - usually 8 ohms. 16 divided by 8 equals
2 watts out.
The dial you see here is the volume control on the Theater Amp. Each channel has its own power supply, and a separate volume control for each channel. There are three scales. One scale is for "Zero" Negative feedback, or NFB. I explain this again : negative feedback is the process of taking a small percentage of the amp's output, and taking it back to a point in the circuit where the sound wave is 180 degrees out of phase. This serves to eliminate any spurious noise caused by the circuit itself. It also has the effect of widening the bandwidth. Now if the parameters of the tube dynamics are set up well, and the tube itself generates pleasing harmonics...which tubes naturally do...then it is not necessary to employ NFB at all.
A final note about "Negative Feedback"-although almost all amps employ this method to cancel unwanted distortion or harmonics-it must be remembered that in order for a sine wave to cancel out another sine wave, ( or more precisely...the very much smaller sine waves to the sides of a fundamental frequency ) the opposing wave must be brought to within SixTen Thousandths of One degree. That's pretty precise , isn' it? It is routinely done with costly Distortion Analyzers to see what is left after cancellation- this would be "distortion". As mentioned above, tubes produce 2nd and 3rd harmonics, which are not so unpleasant to the human ear at all. Solid state audio, by comparison, produces "Odd Order Harmonics"= such as 5th 7th,9th...these are not so pleasant; thus it is of critical importance to employ big doses of negative feedback.
But here is the problem: audio goes through capacitors, which shift frequencies, depending on the frequency! Where audio goes through transformers, an opposite shift takes place with the original audio signal ( this happens in tube amps via output transformers ). The trick is, how does one bring back NFBto a point 6 ten thousandths of one degree where it needs to be, if the phase is constantly shifting with thewide ranging musical spectrum ?
Now, perhaps, you see the beauty of an amp that does not require negative feedback..such as the Theater Amp described above. It really and truly is far superior to- my ear at least. I am reasonably confident that you will discover the same sensation.The theater Amp does permit the selection of minus 7 db NFB, or -13 NFB...or "Zero" feedback...so you can decide. Sometimes, namely with wives...they seem to prefer the music to be "background music". So here, some NFB is a wise choice.
The HP AC Voltmeter above is measuring 4 volts AC on the 10 volt scale ( the other arrow in the middle is a calibration knob and should be ignored ) A pure sine wave is supplied to the input of the Blueberry Amp, which is amplified to 4 volts RMS at the Output of the Amp. This = 2 Watts. Power,Watts, isdetermined by the formula
P = E squared, divided by ohms . Speaker at 8 ohms, 4 X 4 = 16...diveded by 8 = 2
Much more on the math for tube amps page. Much more on how the tube amplifies on my page devoted to "Inside the Vacuum Tube"
Below you see a 24 step "atttenuator", volume control. This inserts only two precision, low noise resistors for each volume level. It also happens to increase sound pressure level "SPL" by about 3 decibels per "click". Each 3 decibel SPL increase is actually a doubling of wattage, approximately at least. This device does make a click , or 'pop' sound, so I am not entirely happy with it...but it does provide me with the three scales of loudness, one scale for each of the negative feedback settings "NFB" , and a fairly precise indication of watts out. Over time, one arrives at ideal SPL settings -although it must be noted that different sources of audio signal can vary quite a lot.
Below you see the 100 milliamp meter , one for each channel of the Theater Amp. It reads 80 ma. This is the ideal current draw for the 300B; the ideal voltage at the anode is 420VDC. At "Aquiesence" or "no audio signal conduction"...the B+ voltage at the plate/anodefalls to approx 340 VDC. This remains constant.
There is no critical need to have an ammeter in the cathode circuit of the 300B...but it does serve as an indicator that "all is well". If you see this meter 'bounce' or is not at 80 ma...then either something went wrong inside the amp...or more likely, the audio source is too high in voltage feeding into the input of the amp...or you have the amp turned up to its highest wattage, which causes "clipping". Normally, the meter remains a rock steady 80 Ma.
I have played this amp every day and night for 2 years...TV, Music, and headphones late at night. I fully guarantee satisfaction, and rock solid stability electronically.
