Rosie – A JTM45/1987 hybrid amp

Here’s another amp I worked on some time back. Her name was “Rosie”, named after the AC/DC song. I had a fixation at the time in trying to nail down the sound of Angus Young, getting an SG and all, and reputedly he had used a JTM45 amp at the time, so that became the basis for this amp.

jtm45ish-1-stack

Another guitar hero of mine is Jimmy Page, and he used a 1987 amp, which is a further development of the JTM45. There are differences between the two and I tried to take the best of both and incorporate them into this amp.

jtm45ish-16-front

I got a chassis online and won the Marstran transformers on Ebay. I kept the tube rectifer and KT66 output tubes inherent to the JTM45 and added a switch to sub in 1987 style tone caps and pre-amp circuitry. I also added a bias test point at the rear.

jtm45ish-17-rearpanel

I had planned to move everything to a different chassis and then build a cab but I sold it on and started working on something else. It was just too much of everything for me; too big, too loud; to heavy. It took a lot to drive it to distortion and though I have compliant neighbors, I think hearing me crank out “Communication Breakdown” over and over must haven got annoying.

I drew up the circuit and layout out for turrets in Autocad. The transformers, choke and tubes were placed in the standard location. I chopped and changed as I went, adding switches and swapping tubes.

jtm45ish-2-circuitboardjtm45ish-3-preampjtm45ish-4-powersupplyjtm45ish-5-poweramp

Here are some photos of the amp in one of its various iterations:

jtm45ish-6-gutsjtm45ish-14-volumepotsjtm45ish-13-switchesjtm45ish-10-powertubesjtm45ish-9-preandpijtm45ish-8-preampsupplyjtm45ish-7-preamp

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