Listening Impressions
These amplifiers are the most musical-sounding amplifiers I have built in my 35+ years of designing and constructing vacuum tube audio amplifiers, and others who have built them seem to concur.
They provide a very colorful “Kodachrome-like” musical presentation, with incredible clarity, liveliness, tonal balance, and a great portrayal of space within the recording venue.
There is no grainy-sounding intermodulation distortion, or the dreaded electronic or mechanical sound, largely due to the incredible linearity of the driver and output tubes, the purity of the power supplies, the quality of the component parts, and the overall design and implementation of the circuit.
They don't "homogenize" the music like so many high-end power amplifiers do; you hear the recording for better or for worse, and every recording sounds completely different tonally, spatially, etc., which is of course the way it should be.
Bad sounding recordings tend to sound more listenable when taking a trip through a pair of transformer-coupled directly-heated triodes with the WE Ultrapath circuit.
The “magic of mercury” vapor tube rectification, with its intrinsic passive voltage regulation/constant voltage drop vs. load current, along with the low DC resistance of the filter chokes, provides a very low source impedance of the driver tube and output tube power supplies, without having to resort to bad sounding silicon diode rectifiers and active voltage regulation.
This gives these amplifiers a fast, powerful, dynamic sound, with deep, solid, cleanly articulated bass. Microdynamics are rendered very naturally, and the electrostatically-shielded power and filament transformers keep most of the noise present on the AC input from finding its way into these amplifiers, with the result that the music comes from a deep black background.
There is never any listening fatigue. Due to the purity of the sound, my wife and I can sit for hours at a time, becoming completely engrossed and enthralled by the music.
I always look forward to listening to music through these amplifiers and their associated equipment, instead of watching the television, or engaging in other forms of entertainment. Our stereo systems should be fun and enjoyable to listen to for as long as we wish, while continuing to provide an ever-increasing appreciation for the music we listen to!
Isn’t that what it’s all about?
As I like to say, you reach a point with this kind of amplification where you become totally at the mercy of the skill and taste of the recording and mastering engineers, and the quality of their equipment. They are that revealing.
Parts List, Amplifier Unit
C1, C2 Capacitor, 25 uf @ 370 VAC, GE Type 97F9006, Polypropylene & Oil
C3, C4 Capacitor, 50 uf @ 370 VAC, GE Type 97F8069, Polypropylene & Oil
CCR1 Rod Coleman 2.5 VDC Filament Constant Current Regulator Assembly
CCR2 Rod Coleman 5.0 VDC Filament Constant Current Regulator Assembly
R1 Resistor, 2200 Ohm, 12 Watt, Wire-wound
R2 Resistor, 880 Ohm, 50 Watt, Wire-wound, Chassis-Mount
T1 Transformer, 150/600 Ohm to 70K/84K Ohm Line-to-Grid Input. Peerless Type 4665, Peerless type K-241-D, Altec-Lansing Type 15095, or suitable equivalent. Secondary to be rated for use into an unterminated grid. See notes in above text.
T2 Transformer, Tango Type NC-20 Driver/Interstage, or ISO NC-20F II, or equivalent. 5000 Ohm, 25 MaDC Primary; 5000 Ohm Secondary. Secondary to be rated for use into an unterminated grid.
T3 Transformer, Tango Type X5-S Audio Output, or ISO FC-40-5S, or equivalent. 5000 Ohm Primary, 100 MaDC Primary Current Rating; 4-8-16 Ohm Secondary
V1 Vacuum Tube, Type 45 or 245/345. The use of the earlier globe- style type 245 or 345 tubes, or the new beautiful sounding EML mesh-plate 45 are recommended, for somewhat better fidelity.
V2 Vacuum Tube, Type 300B. The use of the original Western Electric 300B is recommended for long-term reliability and sonic quality. Also consider the new superb sounding EML mesh-plate 300B.
Parts List, 45-300B Amplifier Power Supply Unit:
A1 Rod Coleman Raw DC Supply Assembly, for 300B Output Tube
A2 Rod Coleman Raw DC Supply Assembly, For 45 Driver Tube
C1-C6 Capacitor, 50 uf @ 370 VAC, GE Type 97F8069, Polypropylene & Oil
D1 Diode, Type 1N4007 or equivalent
D2, D3 LED, Red (Filaments On, & HV On)
F1 Fuse, 2A, Slo-Blo
F2 Fuse, 125 Ma, Fast-Blo
F3 Fuse, 100 Ma, Fast-Blo
L1-L6 Filter Choke, 10 Hys @ 120 Ma, 110 Ohms DCR. Note that the DCR is critical, to ensure the correct plate voltage under load for the 300B and 45 tubes. UTC type CG-100 or equivalent.
P1 Power Connector, IEC, Male
R1, R2 Resistor, 5K Ohm, ½W
R3 Resistor, 2K Ohm, 10W
R4, R5 Resistor, 22K Ohm, 50W, Chassis-Mount
SW1 Switch, Filament Power On-Off
SW2 Switch, High-Voltage On-Off
T1, T3 Transformer, Power, Electrostatically-Shielded
Primary: 120 VAC
Secondary: 880 VCT @ 200 Ma; 5V @ 3A; 6.3VAC @ 6A
T2 Transformer, Power, Electrostatically-Shielded: Hammond Type 266L16
Primary: 120 VAC. Secondary: 8 VAC @ 4.4A
V1, V2 Vacuum Tube, Type 83 Mercury Vapor Rectifier
V3, V4 Vacuum Tube, Type 6AX4GT
If you share or build this circuit, please give me the credit for the design, but this design may not be reproduced on a commercial basis without my formal permission!
I am aware of several other DIY ultra-fi enthusiasts who have built this amplifier, and they were really enthralled with the sonic results.
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