This is a later vintage (1989) MESA BOOGIE© 50/50 Stereo Power Amplifier as designated by the blue power indicator lamp and 4H Choke mounted to the Chassis Bottom. This Amplifier was originally designed for use with Mesa's Quad Preamp and then re-designed and re-voiced by MESA to better suit the later released Mesa TRIAXIS Tube Preamplifier.

Here are some of the modifications integrated into this specific amplifier to make it easier to service and operate…

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BIAS-Mod

I drilled the 50/50 front panel to accept four Bias-Test-points for each of [4] tubes, a Hi-Voltage Test-point for the B+ voltage and a ground test point (There are no dangerous voltages on these test points so you can use a standard voltmeter set to the 200mV Scale to make the measurements.)

 

I also installed four 1-Ohm Cathode resistors installed between the power tube’s Cathode and Ground to facilitate the measurement of the Cathode Current.

 

There is also a custom circuit board with the new Bias Supply resistors and Capacitors. (This is required to split the stock bias supply to feed each channel separately allowing you to set the bias separately for channel A & B)

 

The front Panel was also drilled for two 50k-Ohm bias control pots, one for each channel. Those controls allow you to set the bias for any manufacturers tubes, (including Mesa Tubes) for optimum power.

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BIAS-Monitor Break-out Connector

A 9-pin DIN connector was mounted on the 50/50 rear panel to allow connection via ribbon cable to a Custom 19” Rack-mount metering panel that allows the user to monitor the Cathode current for each tube and the B+. This 9-pin DIN connector parallels all of the new Front-Panel test-points.