Amplitude Audio

Check out this beauty! This 1975-ish Fender Bronco (VibroChamp) came in requiring a new AC mains cable. When the mains cable present in any amp has the outer plastic insulation split in several places revealing the inner wires, it's time for a new one. The amp was wired with the neutral fused when it arrived, so it was re-wired with the live fused first and both neutral and live are now switched. The mains AC ground was also originally mounted on a transformer mounting bolt - not a safe practice - and is now attached to the chassis at its own dedicated ground point. Because the amp was being used on some road dates, bear-trap retaining clamps were also installed on the power and rectifier tube sockets to ensure reliable tube pin to socket connectivity. Thanks very much !

Part 1 of 2: BEFORE

In the world of guitar amplifiers, most people would likely be familiar with brands such as Fender, Marshall, Vox. Earth Sound Research - likely not, nor was I until this beauty showed up to the shop. Earth Sound Research was a company from New York that built amps for a few years in the 1970's. The ESR Super Guitar G-2000 was one of their offerings and was basically a clone of a Fender Twin Reverb housed in a Kustom-esque tuck-and-roll vinyl clad exterior that would have looked similar to car seats of the same period.

The amp came in with crackly front panel controls, no reverb or tremolo, an original two-prong AC cable that needed replacing and a good cleaning. After taking a look inside it was clear that this amp hadn't been opened up since the day it left the manufacturer - original tubes (I'm pretty sure), capacitors with a 1973 date code and a hand-written date of December 15, 1973 that was probably added by whomever wired/inspected it prior to it leaving the factory.

Many of the electrolytic caps were bulging and all needed replacing, the screen resistors had split in half, almost all of the original components' values had drifted way beyond their spec, and the grounding throughout the amp would have created a noisy mess. After chatting with the owner of the amp, we decided to give this gem a new lease on life and completely rebuild it. Although some people liken point-to-point wiring to unicorns and rainbows, in this case, maintaining this wiring scheme in a rebuild with some circuit modifications and a better grounding scheme wouldn't have worked. The owner wanted one channel to keep the classic Fender tone and one channel to have some Marshall kerrang. As a result, the decision was made to gut the amp down to the studs and build it back up with tone, serviceability and reliability in mind. Stay tuned for part 2.