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MC77 Parts
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The MC77 PCB has the same audio path as the MC76 (or a vintage 1176), plus locations for components that enable extra features. Along the front edge, there are holes for a metal board stiffener (shown seperately in photo), which prevents potentially damaging flexure. The silkscreen indicates all component designations and most component values, for ease of service.
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The input attenuator is a custom 3 deck pot, configured as T-pad. It is a functional equivalent to the bridging T-pad found in the original revisions A-F 1176 and the MC76. Unfortunately, the company that made the bridging T-pad, which was a 2 deck pot with two fixed resistors, is no longer able to get the unusual taper resistive elements that were needed for the part. The 3 deck non-bridging version is electrically equivalent, but more expensive due to the extra deck required. The action on the three deck pot is also much smoother than the original.
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The input transformer is a PCB mount replica of the original UTC O-12 (the O-12 is shown in the O-17 mu-metal shield, with can clamp). UTC went under and was gobbled up by larger companies, uninterested in making audio transformers, years ago. After years of buying and checking NOS and used O-12s, we were finally able to have an exact replica custom wound for us. The core inside the can has been changed from a vertical to horizontal orientation, for a wider and lower mounting profile. In listening tests, we have found that the new version matches the original.
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The output transformer is an exact replica of the unit found in the original 1176. We eliminated the extra wiring for the unused output center tap, and added end bells for extra protection. Other than these minor changes, the transformer is the same as you would find in an original 1176, without any unnecessary "improvements." This transformer has a very unique design, including a tertiary feedback winding, which you will not find in any off-the-shelf transformer.
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The power transformer is a custom wound toroid, with dual primaries for 230v/115v operation, and dual secondaries at 40VAC each. Most readily available toroids in this size do not provide a high enough voltage at the secondary, especially for regions with low line level power (100v in Japan for example).
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The level and gain reduction meter is a true ANSI spec VU meter made for us in the USA by Hoyt. Unlike many similar looking "VU meters" the Hoyt 3125 has a needle movement that tracks signal level very well, with almost no overshoot or slop. They are not inexpensive, but they are the best real VU meters we have found.
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The meter illumination is a circuitboard with a string of LEDs that spans the entire top of the meter. Unlike the two #1819 incandescent bulbs found in the original 1176 and early MC76 units, the LEDs will last for many many years without needing to be replaced. For more information, see the LED light kit page.
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