Mini Major amp

August 2025

Marshall Major was the amp that Ritchie Blackmore used in Deep Purple and in Rainbow. It was very much modified to suit his personal taste (several times along the years). It was also a 200 W monster that was at his level and at the time great for his needs for live playing. The idea to have a lower wattage amp with Marshall Major tone is intriguing and people have been building these for years. The fact that Major had the B+ voltage over 600V is not easy to obtain and is indeed affecting the tone of the amp. So it seems we have to make some compromises to be able to build a practical and usable amp. 

This is what I'm gonna do:

• Marshall Major Lead or Bass circuit or a mix of both

• B+ voltage below 500V

• Two KT88s in ultra linear class AB fixed bias

• Use easily available transformers (Hammond 290HX power and Hammond 1650RA output transformer)

• TAD 100W plexi head cabinet, chassis, face plate, knobs etc.

• No master volume

• Will do the cascade preamp ('one-wire-mod')  if it sounds good in the amp

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After 4 weeks of working on and off the amp I could finally test it. I had a few typical "how to turn on a tube amp for the first time" type issues like to get the power tubes negative bias voltage to a suitable range and I also had to reverse the plate and screen grid wires to get the negative feedback right. The B+ voltage settled to around 470 V which was just about fine as my filter caps are rated to 500 V. With the plate voltage being around 460 V, I set the plate current with the Gold Lion KT88 power tubes to 55 mA which was 60% of the 42 W max dissipation. That gives me about 55 W of clean power which is just about ideal. I won't play the amp clean but that's the measured clean power.

A few mods right from the start: First thing I changed was the tone stack slope resistor to 56k (bass spec) as I felt the 33k (lead spec) was too middle heavy. The second mod was the 'one-wire-mod' that I occasionally use in my Superlead. After the slope resistor change, the amp started to sound like what I was hoping for, better. Clean is very nice bell like tone and when you crank up the guitar volume, it gets dirty nicely. The EQ in the amp is more responsive than the EQ in Superlead. I will make some demos on my Youtube channel at some point.

This is the beginning of the amp's journey. I'm sure I will keep adjusting the amp to my liking as I did with my Superlead.

As there are no layouts available I had to make my own and I will make them (main board and PS/bias board) available to download as png below (click to open, they are large). The layouts combine info from several sources (photos of original Marshall Major amps, schematics, el34world.com, treblebooster.net etc.). Component values may differ from one version to another. The layouts have been made with the DIY Layout Creator.

If you choose to build it, you will need to have a full understanding of the circuit and be able to verify the layouts. In other words, you will use the layouts at your own risk.