Saturday, May 10, 2008

Eric Barbour or Fred Nachbaur?

Recently, I mentioned in on an online forum my idea for a 15-ish-watt amp based only on Compactrons with a 6AS11 preamp and a pair of 6LU8s for the power amp and phase-inverter (each tube contains a beam tetrode and a medium-μ triode). One response was: "You should get a job with Metasonix". I suppose I could have taken offense at the comparison: While I think there is a place (and probably a need) in the world for a guy (Eric Barbour) who makes an amp called the F*%@ing F*%@er [grawlixes mine], that's not me or my style. Also, amusing as it is, I don't think I could bear to build an amplifier that uses 800 watts of power for just 30 watts of output.

I think the Metasonix comparison really came from the idea of using new-old-stock tubes for other than their original purpose. It wasn't Eric Barbour that gave me the idea, though; it was the circuits and writings of the late Fred Nachbaur. Fred's pages were one of my key resources when I decided to move from repairing & tweaking amps (like a Kalamazoo model 1 and a "Blackface" Fender Bassman) to designing & building from scratch. His design philosophy was mostly rooted in classic methods, but he loved to use oddball tubes, especially ones with atypical heater voltages arranged into series/parallel combinations. That approach seemed to border on obsession in some cases: Just look at the power supply for his "Spunky" guitar amp. It's a pretty cool arrangement that eliminates the need for a transformer with a heater winding. A bit of goofiness though is seen in the two 10-watt power resistors needed to set the voltages right, and the fact that there's an entire separate transformer for the bias supply. I guess it works if you have the parts on hand.

In any case, the all-compactron amp is not going to happen, at least not right away... Since I'm on the waiting list for a new Danelectro reissued '63 Baritone guitar, which will need an amp, I'm going back to a previous idea for the 15-ish watt amp. The power section will be a pair of Electro-Harmonix 6973s. Just like when I chose the JJ 7591S as the power tube for the Lama Kazu 8SE, (7591s are rarely seen in single-ended amps— they mostly turn up in old Ampegs) I couldn't bear to use the typical EL84 or 6V6 power tubes that are more common in amps of this size. More to come on that project.

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