Overview
Treehaus Audiolab has chosen the venerable 300B as the power tube in our amplifiers. The 300B offers the power and headroom needed for dynamic music passages on high efficiency speakers; whilst managing the magic of smaller triodes. The 300B circuit we use has been tuned to eliminate some of the syrupy sound this tube can express on some of the more classic circuits; it has more of the character of a 71A/ 45/ VT-52, but with the energy only a larger-plate tube can provide.
Finemet transformers are used in Treehaus Audiolab 300B amplifiers, made for us in Japan. Extensive benchmarking within our Lab showed these transformers have no equal. The sound is clean, pure, with no etch. A Finemet interstage couples our driver tubes to the 300B; no capacitors are in the signal path. A large Finemet output transformer performs impedance-matching duty.
Cardas connectors are used for the RCA inputs and speaker outputs. Amtrans resistors are used in the capacitor-free signal path. A high-mass 6mm CNC-milled aluminum plate secures all components.
New production Western Electric 300Bs and appropriate NOS tubes are supplied with each amplifier.
Treehaus Audiolab 300B SET Amplifiers are available in 3 variants. Each can be built in either the Kinsuido style or the A/Machines style. Kinsuido is influenced by 1970’s Japanese Hi-Fi and MCM aesthetics, and the A/Machines visually pays respects to early Western Electric and Klangfilm equipment.
300B-1 SET Amplifier
This amplifier builds off our experience with transformer-coupled and Sakuma-inspired SET designs in a compact, one enclosure design. Superlative audio performance in a more accessible footprint.
The venerable C3M tubes function at the core of the gain stage. This tube was created as a “no compromise” design by the German Post for telephony use. With more drive capability and better specifications than the typical tubes paired with 300Bs, it is a fantastic sonic companion. The beautiful mesh plates are simply icing on the cake for this wonderful tube. The C3M drives the 300B through a Finemet interstage transformer; free of coupling capacitors. The 300B outputs through the same over-spec Finemet transformers we use on our other amplifiers.
Despite the compact footprint, the power supply section is robust. 5AR4/ GZ34 provides DC rectification. The CLCLC configuration, utilizing both film and Mundorf HV+ capacitors, smooths and cleans high voltage power. Regulated DC heater circuits minimize filament noise and ensure long tube lifespan.
The result is sound that captures the magic and sonic bliss of the 300B, without the excess bloat, bloom and noise that accompany typical “period-correct” topologies.
The 300B-1 Amplifier shown is in the Kinsuido style with Oxidized top-plates and wenge hardwood cases.
300B-2 SET Amplifier
The 300B-2 Amplifier separates the signal section and power supply section into two enclosures. It utilizes a Directly Heated Triode (DHT) driver interstage transformer-coupled to another Directly Heated Triode acting as the power tube. This design is based on the work of the Japanese master-of-the-art Susumu Sakuma, with a deep reference to the earliest Western Electric designs. Sakuma recognized the symbiotic sonic relationship that forms when a DHT drives a similar DHT. The pleasing distortions of the second harmonic are enhanced while less desirable harmonics are minimized in this configuration. The architecture yields one of the purest expressions of what vacuum tubes can offer the listener.
We chose to use the 10/ 801A series of tubes for the driver: This tube is extremely clean sounding, offers a strong amplification factor within the DHT family, and with quite a few varieties, allows for some unique tube-rolling opportunity.
The separate power supply utilizes several power transformers within it for different circuits within the amplifier. A GOSS core high voltage power transformer offers clean voltage stepping with excess capacity. A pair of 6CJ3 provides high-speed DC voltage tube rectification to the audio circuit. Finemet chokes and a unique combination of film, electrolytic, and oil capacitors clean and provide a deep storage well of amplifier power. High quality filament power is essential for Directly Heated Triodes: as their name states, the tube heater is directly tied to the cathode of the tube. Unlike an indirectly heated tube, the heater is tied to the audio amplification circuit. We utilize separate AC/DC supplies for each tube in the 2-box design, with Coleman filament regulators to provide ideal power to the heater. LED displays or analog gauges on the amplifier allow for easy setup and adjustment of this critical voltage application.
The 300B-2 Amplifier shown is in the Kinsuido style with Oxidized top-plates and wenge hardwood cases.
300B-4 SET Amplifier
TThe 300B-4 Amplifier is conceptually similar to the 300B-2, with a DHT tube driving the 300B. It departs from this design by using 4 enclosures rather than 2. Each channel is two units: one amplification section and one power supply section. The ultimate layout for noise and channel separation. To keep it simple, we simply doubled the total tube-rectified power supply capacity compared to the existing design. The signal section utilizes special “high Teflon” Finemet transformers. The result is everything loved about the 2-Box design amplifier, just more of it. More energy, more detail, more clarity, more nuance, more refinement, and still with plenty of SET magic.
The 300B-4 Amplifier shown is in the A/Machines style with Oxidized top-plates and silver hammertone cases.
Specifications and Pricing
300B-1
One Enclosure Design
C3M interstage driving 300B
EL Power Transformer and Chokes CLCLC
5AR4/ GZ34 Rectification
Finemet Interstage (small) and Output Transformers
Regulated DC filament supplies
Mundorf HV+ Power Capacitors
Compact footprint
Input Sensitivity: 6W @2.8VRMS
THD: 2.2% @6W
S/N: 95dB @6W
Frequency Response: 20-20,000Hz +/-0.5dB
$16,000 Including WE300B, C3M, and 5AR4 tubes.
300B-2
Two Enclosure Design
10Y/801A interstage driving 300B
GOSS Core Power Transformer and Finemet Chokes CLCLC
6CJ3 Damper Diode Pair Rectification
Finemet Interstage (large) and Output Transformers.
Coleman filament regulators with individual DC supplies
Mundorf HV+, Film and Oil Power Capacitors
Amphenol MIL-SPEC Power Umbilical
Input Sensitivity: 6W @4VRMS
THD: 2.2% @6W
S/N: 95dB @6W
Frequency Response: 20-20,000Hz +/-0.5dB
$24,000 Including WE300B, 801A, and 6CJ3 tubes.
300B-4
Four Enclosure Design
10Y/801A interstage driving 300B
GOSS Core Power Transformer and Finemet Chokes CLCLC (x2)
6CJ3 Damper Diode Pair Rectification. (x2)
Finemet Interstage (large) and Output Transformers (high Teflon)
Coleman filament regulators with individual DC supplies
Mundorf HV+, Film and Oil Power Capacitors. (x2)
Amphenol MIL-SPEC Power Umbilical (x2)
Input Sensitivity: 6W @4VRMS
THD: 2.2% @6W
S/N: 95dB @6W
Frequency Response: 20-20,000Hz +/-0.5dB
