AC30BM redesign and rebuild

 

In 2011 I designed a new version of my Brian May AC30, the tagstrips and power/preamp sections were designed to fit into the JMI styled chassis of the Chinese made AC30BM amp. The amp also included a new master volume control which was different to the Matchless style ‘drive lines summing’ master volume control that I had been using from 2003-2010 on my We Will Rock You production AC30s and also on Brian May’s own AC30s. (more about the master volume control later)

The first amp was built for Kazutaka Ijuin from Kz Guitar Works in Japan. As with my other WWRY and Brian May handmade AC30s, the whole amp was built from scratch by myself and retained just the metal amp head chassis and speaker cabinet from the original amp. Martin Kell’s and Paul Voller’s custom handmade Australian transformers were used again same as with the WWRY and BM amps from 2003-2010, this time the mains transformer was wound by Martin for the Japanese 100V AC mains power.

(more info soon)

AC30BM power amp and rectification section #1

AC30BM power amp and rectification section #1

AC30BM preamp #1

AC30BM preamp #1

AC30BM testing November 2012

AC30BM testing November 2012

AC30BM head rear #1

AC30BM head rear #1

AC30BM testing #2

AC30BM testing #2

AC30BM testing #3

AC30BM testing #3

The extra hole on the top section was for a mod that Kazutaka was considering adding later. Each push-pull pair of EL84 valves have their own fuse and LED indicator same as per my WWRY and Brian May AC30s.

EL84 cathode fusing:

If an EL84 blows up and trips the fuse (which usually happens when its screen grid starts to fail and begins to pull steadily increasing amounts of current through its 330 ohm/3watt metal oxide screen grid resistor), that push-pull pair is disconnected and its LED lights up. The amp will still continue to work as usual and will sound pretty much the same even on just one push-pull pair of EL84s. Two WWRY guitarists told me a few years ago that they played a couple of shows just on one push-pull pair of EL84s in their amp and didn’t notice that the red LED was showing on the top panel. Both told me that they didn’t notice much difference in the sound until they saw the red LED and later replaced that pair of EL84s. Both players said that the amp sound was a little fuller with all 4 EL84s working properly but were surprised at how good the amp sounded on one pair of EL84s.

This function was designed with the We Will Rock You theatrical shows in mind because of their obvious need to get through the show regardless. The EL84 fusing began based on ideas from Kevin O’Connor and Dave Peach.

AC30BM EL84 cathode fusing and standby switch

AC30BM EL84 cathode fusing and standby switch

AC30BM view from rear of preamp and power amp underneath

AC30BM view from rear of preamp and power amp underneath

AC30BM star earth on steel chassis power amp section near mains tx

AC30BM star earth on steel chassis power amp section near mains tx

AC30BM chassis drilling #5

AC30BM chassis drilling #5

AC30BM chassis drilling #2

AC30BM chassis drilling #2

AC30BM preamp tagstrip holes drilling #4

AC30BM preamp tagstrip holes drilling #4

more to come…..