TrainWreck Rocket: 1. Redesigned

The trainwreck rocket is a highly coveted and copied guitar amp, however it, in part, is a copy itself. It is the core of a vox ac30 and where made by Ken Fischer. Here I design my interpretation. Ken started by singling out the best part of this classic amp, the ac30, by careful construction and component selection your left with a really nice amp for clean breakup tones and ‘chime’. After my dumble and Soldano slo builds this is another must-build although it’s nowhere near as challenging.. And thus I must make it challenging to keep things interesting, redesigning it for my needs and tastes.

Summarised, the main changes are, firstly, that I want to keep the volume down by halving the number of output valves, and then running JJ EL844’s, bringing things down a little bit more. Second, the original has an unused tube stage, so I’m adding that to the circuit as a second channel. And thirdly, I am interested in the typical and rare vox sound using the odd Ef86 preamp tube, so adding that as a separate first stage option. Lastly I’m basing it on a platform of the ‘Z-wreck’ an interpretation of the rocket by the amp brand and designer ‘Dr Z’. So what’s left is a redesign based on, a redesign 1 of a redesign 2 of the vox ac30 top boost channel. Really a good example of how amp designs progress, iteratively, with some revolutions now and then (Alexander Dumble, Mike Soldano, Reinhold Bogner, Larry Grohman, and Ken Fisher to name a few). And I’m not the first to consider these specific additions/changes, however I also want them all in the same amp while minizing it in other ways by further removing/substituting parts of the previous designs.

The working design is something like this sketch here, bound to be changed down the line and include one or two errors in this versions. Removing the choke and the rectifier tube is two nice space savings, which require some parts to mimic tube sag supplied by the rectifier tube, as well as possibly some extra filtering by using a dropping resistor in place of the choke. So in a way the build is progressing and may be updated as I go along.

I still haven’t made my mind up on the switching, wanting both an Ef86 channel and a top boost channel from the ac30 as well as the extra gain channel with the un-used tube stage. There is a possibility, f. i. to use the same gain pot for both boosted or un boosted, with or without the extra tube stage. Switching could also be managed by relays, as I have a good power transformer for this to use. Thanks to the very popular DIY marshal project (’18w’) there are good useful transformers around cheap enough and with power to do fun things like relays in low wattage amp’s suitable for a two-tube el84 base. In other words ideas exists yet this base sketch is complete and next I’ll cover the making of a very special headshell/case for this amp.