Marshall MA50 Standard Retube

PLEASE READ THE TEXT BELOW THAT EXPLAINS THAT YOU DO NOT NEED TO USE A BIAS PROBE!!!!!

The MA series 50 watt amps are biased between 40 to 45 Millivolts per side at the factory test points using a Multimeter. 

You can use the Marshall DSL100 bias video for reference as the bias procedure is the same. Unfortunately Marshall decided to locate the trim pots on the MA amps inside the amp, so you must pull the chassis to bias it. The middle prong is your ground. 

The most asked question we get is "do I need bias probes that are like the ones shown in this video to bias my amp." The answer is no. If you listen to the video we will explain that we're showing two different methods of reading bias and showing the probes and meters so you can get a better visual  on how the bias works. All you need to bias one of these amps is a simple multimeter to do the job.

The second most asked question is "what setting do I use on my multimeter" The answer we give in the video is Millivolts!

The third most asked question is "do I use the black or negative lead for the middle test prong?" The answer is yes!

The fourth most asked question is "do I bias the amp in standby?" The answer is no! The amp must be in the play mode to adjust the bias.

The fifth most asked question is "do I have to have a speaker plugged in?" The answer is YES! You MUST have a speaker load on the amp.

The sixth most asked question is "what do I bias KT77's at?" The answer is EL34's, E34L's, KT77's and the big bottle JJ 6CA7's all bias up to between 40 to 45mV per side.