Tube Amp 6SL7 & 6BX7 SET
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Stereo Tube Amp - Single EndedTriode 7 watts
A Stereo Tube Amp, also suitable for a guitar amp if a preamp for guitars is utilized.
This amp employs the early model triode vacuum tube since it is recognized to be a very musical tube, producing 5% harmonics. Negative Feedback ( a portion of the output applied 180 degrees out of phase at a certain point in the circuit-cancels out much of the harmonics. One can choose to leave all the harmonics in-but this amp reduces the harmonics to a subtle and pleasant "point 2 % ".
Purity Test
Point to point wiring plus printed circuit board
The Blueberry Amp
Front Panel - Headphone Jack
LED's Fire every 3 decibels of SPL
The Blueberry Amp $1800 each
Art Deco Version of the Blueberry Amp
Drawing of Wiring for the Tube Amp Kit Builder
More Drawing of Wire Connections for the Kit Builder
Blueberry Schematic : Kept unreadable-must be paid for
Sample Photo 11
300B Tubes from the 40's for movie theaters
If you are still with me, this big amp with the big tubes are reproductions of a tube developed in the 40's for the movie industry - to fill a large theater with BIG sound. It happens to be the most musical tube ever made-owing to the long filament, the long grid wire, and the large anode plates. So highly revered by the discerning audiophiles, that these tubes fetch a price from $500 / pair to just over $1,000 a pair.
Vacuum tubes became smaller, and even more powerful with extra grids to accelerarte electrons, and even plates with negative voltage to "focus a beam" of electrons toward the anode.These tubes are SO very musical , with pleasing harmonics...and big power-vis 420 volts + DC on the anode. This was before hot filaments with 2 volts AC and high amperage glowing orange hot, and boiling off electrons via the thoritated tungsten. Thorium is the second step down from Uranium-so you get the idea of massive quantities of free electrons. A certain amount of AC "hum" is heard on these amps. Later the filament was enclosed inside a slender tube grounded so as to divert the hum from getting to the speakers.
If vacuum tubes had NOT been designed to be smaller than these are, a TV, which came later, would have to be the size of a refrigerator ! But it is the largeness of these tubes that make them so desirable for music. Again, the high voltage plays a role in the power of these amps. The circuit is kept ultra simple, so that there is dramatically reduced probability for the circuit to effect the purity of the original recording. One's audio source, typically well under one volt AC...is sumptuously amplfied in only one stage of amplficationvia the 6SL7 tube-which then drives the large 300B with a huge voltage swing.
Have you ever seen a volume control knob this fancy? Note the switch below the knob. This allows the selection of small negative feedback, or moderate NFB, or NO feedback ! I come to prefer zero NFB...THIS is what brings the musicians into the room with you...so to speak.Naturally, there are three scales for the volume control - each scale represents the actual wattage applied to the speakers, depending on the amount of NFB you choose
HP AC Voltmeter : This is specifically for accurate measuring of a sound via audio signal generator either into or out of your audio amplifier. Here the meter is reading 4 vac output from the amplifier. Power, Watts perchannle. is found by "squaring" the 4vac...divide by the speaker impedance/resistance- which in my case is 8 0hms....you get 2 watts. ...(disregard the middle knob arrow...the arrow in question points to the "10 volt scale" )
The all important Oscilloscope.
