5.) The correct bias reading in "Single-Ended"mode is 550 mVDC. A reading of

540-560mVDC will be within specs. The bias in single-ended mode was set at the factory.

If, however, the S-E bias reading is out of spec after warm up, the bias may be adjusted as follows: 6.) Carefully turn the amp on it's left side, Be sure to brace the amp so as to prevent roll over.

7.) Locate the 1/4'' round hole in the bottom cover, near the front group of ventilation slots.

8.) Make sure the amp is in S-E mode, warmed up, muted and with voltemeter attached. Then insert a 1/8'' - 3/16'' slot screwdriver through the hole. Rotate the screwdriver until properly seated. The control is about 2 inches below the cover plane. A screwdriver guard is provided to prevent accidental contact with other components.

9.) Slowly rotate the screwdriver while watching the meter reading. The meter may be in either "read bias" tip jack. Clockwise increases S-E standing current. Adjust standing current until meter reads 550 mVDC.

TUBE REPLACEMENT:

Should the 300B tubes require replacement (or the originals are not returned to their proper sockets), make sure both bias adjust trimmers are turned fully clockwise before applying power to the amp. Then follow the bias procedure outlined above. The bias should be checked daily on a new set of tubes for the first week of operation. Remember to let the amp warm up for 20-30 minutes before making final adjusments. The 5U4G, 6SN7 and 6SL7 require no adjusments.

FUSES

There are two fuses in the amplifier. One is the mains fuse located in the AC input module on the rear panel. The other is a P-C board mounted B+ fuse inside the amplifier. The fuses used in your amplifier are standard 1/4" x 1 1/4" SLO-BLO types. The correctly rated fuse has been installed at the factory for your country's voltage. If replacing a fuse, always unplug the amplifier's power cord from the wall outlet and always use the exact same type and ampere rating fuse as the one you are replacing. Failure to do so will void your warranty and can be a dangerous fire hazard. For 117 volts mains correct fuse size is 3A slow/blow 3AG. For 240 volts the correct fuse is a 1.5A slow/blow MDL 1.5A for the mains.

The internal B+ fuse is a 400mA 3AG ceramic body type unit. If this fuse blows, the tube filaments and badge lamp will ligth up, but no sound will be heard since the high voltage will be absent. If this fuse fails, it indicates trouble which will generally require technical attention. Contact your dealer or Manley Laboratories if this problem should develop.

Caution ! High voltages and high energy storage makes opening the amplifier enclosure hazardous for any uninformed person ! Call us or your dealer for specific instructions or for answers to any questions.

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Manley Labs 300B owner manual Tube Replacement
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300B specifications

Manley Labs 300B is a high-fidelity tube amplifier that has gained a reputation among audiophiles for its exceptional sound quality and craftsmanship. This amplifier is named after its use of the 300B vacuum tube, a component famous for producing a warm, rich sound that is both detailed and engaging. The Manley Labs 300B amplifier has become a reference point for those who appreciate the artistic qualities of sound reproduction.

One of the key features of the Manley Labs 300B is its fully balanced design, which helps to minimize noise and distortion. This design approach allows for greater dynamic range and clarity in the audio signal. The use of premium components throughout the circuit further enhances performance, ensuring that every note is rendered accurately and with depth.

In terms of power, the Manley Labs 300B delivers 8 watts per channel in a class A operation, which is a hallmark of high-end audio equipment. While this may seem modest by modern standards, the quality of sound produced is often more important than sheer wattage. The 300B’s output stage offers a creamy and dynamic sound, excelling particularly with vocal and instrumental music, where it conveys subtle details with remarkable fidelity.

Another significant aspect of this amplifier is its flexibility in terms of speaker compatibility. It is designed to drive a variety of speakers, making it a versatile choice for different listening environments. The Manley 300B supports both 4 and 8-ohm output impedance settings, allowing users to match it to their favorite loudspeakers for optimal performance.

Additionally, the amplifier's construction is noteworthy. It features a robust chassis that not only reduces resonance but also adds to the overall durability of the unit. The hand-built nature of the Manley Labs 300B ensures that each piece is crafted with meticulous attention to detail and quality.

The Manley Labs 300B also comes equipped with a rich array of features, including an input selector, volume control, and high-quality binding posts for speaker connections. These components are not just functional; they also reflect Manley’s commitment to providing a user-friendly and high-performance experience.

In summary, the Manley Labs 300B is a sophisticated and beautifully crafted tube amplifier that offers a level of sonic performance that is hard to match. Its combination of high-quality components, thoughtful design, and powerful performance make it a standout choice for audiophiles seeking a true musical experience. Whether used in a dedicated listening room or as part of a larger audio setup, the Manley Labs 300B delivers a sound that is both engaging and lifelike.
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