ToneDoctor's First Born 18 amp from Blockhead Amplification is a very special amp...it's been our #1 for a long while now. It's a 2x12 combo, loaded with a pair of 8 ohm Celestion G12 Blue Alnico speakers, Mullard 12AX7's, Mullard EL84's, and a Mullard EZ81 rectifier tube.
The stock First Born 18 comes hard-wired for a 16 ohm load, with the two 8 ohm speakers wired in series. We designed a simple mod for our First Born 18, to enable switchable access to the 4, 8 and 16 ohm taps on the output transformer, and also provide a parallel speaker out for driving an extension cab.
This First Born 18 transformer is a Radio Spares clone, patterned after the heralded output transformer used in the earliest Marshall 18 amps. Your tech can easily implement this mod using this color-coded schematic. Of course, the concept embodied in this schematic will also work with other Radio Spares clone output transformers, but you'll have to translate the color codes used on your transformer to those used on the First Born 18 using this table.
Yeah, our mod uses two switches instead of one, but the switches used are simple and readily available in heavy duty, high quality versions - attributes essential for maintaining 100% tonal integrity - whereas more complicated switches required for a single switch design are not. As always, our choice was to not compromise tone, so we settled on the two switch design.
Our First Born 18 was also modded to enable switching between tube and solid-state rectification. In solid-state rectifier mode, the amp cops a classic Marshall 20 vibe, a somewhat tighter and more aggressive sound than the Marshall 18 vibe. The beauty of this simple mod is, of course, that it gives you effectively two "desert island" amps in a single package!
You can hear Tom Guerra playing this amp, in tube rectifier mode through the stock Celestion Blues in the combo amp cabinet, on the track Sidewinder Walk, off the Mambo Sons latest album, Racket of Three. Here's a clip of Tom "noodling", through the same amp configuration, on our McNaught Black Limba SC (middle PU position). And here's another. Tone is kind of THICK, no?
