They're virtually sealed so spraying deoxidizer spray doesn't do much. My only gripe with the D540 are the input/recording source selector switches. To much and you reduce the amps efficiency (to much overlap). To little current and you get crossover distortion (little to no overlap). The overlap reduces or eliminates the crossover distortion. The only adjustment in the D540 (aside from a level adjust in the pre-amp section) is the idle current which basically determines how much the transistors will conduct on the positive and negative swing of the AC signal.The NPN transistor should amplify just a little more than 180 degrees of the positive portion of the signal and the PNP a little more than 180 degrees of the negative signal. If you have an NPN and PNP output pair, it'll be a class AB. One of the ways to see if an amp is class AB is to look at the output transistors. Getting hold of the service manuals always help. I've been working in the aerospace industry for the last 30+ years but have always enjoyed repairing audio "on the side" so to speak. I've also seen othe bloggers and forum posters state that the transformers are "dual mono".nope. The transformers are configured such, that one supplies the lower (+38V) and higher (+76V) voltages for the positive power supply rail and the other supplies the lower (-38V) and higher (-76V) voltages for the negative power supply rails. The two transformers are not dedicated as one for high power and one for low power. They are the high speed switches that connect the high voltage power supply rails to the output transistors when the DPD circuit activates. Those two smaller transistors on the heatsinks are NOT class A amplifiers. All the Proton amps with DPD like the D540 and AA1150 are class AB amps.Even on the write up for the D540 (which i've had for 34 years and have serviced myself) shows where you misunderstand the DPD circuit. Nice blog but I have to make a technical correction that you and other bloggers with little technical knowledge keep getting wrong.
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