Manley Labs 75/150 SE/PP 807 MONOBLOCK owner manual Operational Notes, Adjusting Bias

OPERATIONAL NOTES

SWITCHING SINGLE-ENDED 75 / PUSH-PULL 150 This amplifier has a feature exclusive to Manley Labs of being able to choose between two circuit topologies. You are able to switch between each mode while the amplifier is turned on and playing music. In SINGLE-ENDED mode the amplifier uses eight 807s in parallel. The advantage is a minimalist circuit requiring no "phase splitter",The disadvantage is a less efficient circuit that produces half the power of PUSH-PULL. In PUSH-PULL mode each tube works in opposite phase to the other and relies on the output transformer to make the polarities work together. This has advantages in efficiency and in the distortion and noise cancellation properties of a balanced circuit. Both ways are operated in "Class A" bias throughout and both are PURE TRIODE and both modes have a similar short signal path.

ADJUSTING BIAS

The amplifier has been factory adjusted and should not need adjustment more than once a month. This does more for tube life than it does for sound quality. You will need a DC voltmeter and a small flat screwdriver. This should be checked every few months but does not need to be necessarily adjusted unless an 807 pwer tube is replaced. Checking verifies that each tube is stable and operating properly. It may be the first hint that a tube is needing replacement.

1) Let the amp warm up in SINGLE-ENDEDmode for about an hour, then with no music playing.... Set the volt meter to a low DC range such as 1 or 2 volts DC.

2) Put negative or black probe of the voltmeter to the black test point (ground),front and center of the amplifier and the red or positive probe in the small red socket most left front near the 807s. See the diagram on the previous page that indicates which test point and trimmer relates to which tube. 3) The meter should read 340 mV or 0.34 volts DC. If not -then you can adjust the trimmer without opening the chassis. It is located in the hole near the transformer and is blue. Adjust it gently and fairly slowly. A little "drift" is normal.

4) Now check and/or adjust the other tube's bias. Use the next right red probe socket and the next right trimmer and adjust the same way. Continue for all 8 power tubes.

5) You may want to re-check each tube's test point and re-adjust if needed. There may be some small interaction - particularly if a tube was replaced.

TUBE LIFE

You should expect many years of life from the tubes in your MANLEY SE / PP if you adhere to the procedures described above and check your bias at least once every 2-3 months. We stock all the tubes in these amplifiers should you ever need replacements (and at very reasonable prices too!)

FUSES

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 120 volts the correct fuses are MDL10 for the mains. For 240

volts the correct fuses are MDL5 for the mains.

INDICATOR LAMP

The lamp is a 1/4" X 1 1/4" fuse style rated at 8 volts and 0.3 amps. Power should be disconnected, the power supply discharged (1 minute). The bottom panel will have to be removed, The lamp is clearly accessable directly behind the semi-translucent Manley logo panel. Gently pry out one end to remove the lamp for replacement.