This McItosh Solid-State Blue LED Meter Lamp Set (two lamps) is for the MR 71, MR 73, MR 74, MR 77, MR 78 Tuners and MC2105 Amplifier. The MC2105 Requires two sets (four lamps)Simple to Install:Installation is straight forward and every attempt was made for ease of installation. This is a direct lamp replacement and can be performed in about 15 minutesAs a replacement for the blue filters I have developed a Blue illumination kit to replace the existing #1847 incandescent meter lamps provided with the McIntosh equipment. The kit consists of two custom manufactured LED lamps designed as plug-in-play replacements for the original #1847 incandescent bulbs. The new LED lamps use the same style bayonet bulb base as the originals. There is no need to replace or add additional gel filters. Simply discard the original gels!Although I have only tried them in an MR-73 they should work with many other McIntosh products which have a clearance hole larger than 0.45 inches. This diameter is required to allow passage of the lamp top diffusion lens through any chassis clearance hole. These lamps are designed as 5.0 to 6.3VAC bulb replacements like the #1847 used for meter illumination in the MR-73.The life of an LED is long, typically 80,000-100,000 hours (almost 10 years of continuous power), and most of us will never experience one going out. Once the original lamps are replaced you should never have to replace them again. You will save on current draw! The two LED lamps only require a total of 40mA whereas the original #1847 lamps have a total of 300mA current draw. That's over one quarter amps less current draw from the power supply and negligible heat dissipation from the LED's.These are not mass produced lamps. Each lamp is hand assembled in my shop. The bayonet bases are solid brass. Lamps have a specially manufactured diffusion lens which surrounds the blue LED. This dispersion lens is milled from solid semi-transparent plastic. It is not a hollow plastic covering! By using a solid lens material the emitted light is dispersed a full 360 degrees around the lamps sides and a full 180 degrees toward the top side. The picture below demonstrates how well this custom dispersion lens works installed in the McIntosh MR-73 tuner. The picture is taken from the top of the dial tuning assembly with the dust cover removed.