Lil Tiger Hammond AO-43 Organ to Guitar Amp Conversion

Published:2013/3/10 21:48:00 Author:Ecco | Keyword: Lil Tiger, Hammond Organ , Guitar , Amp Conversion | From:SeekIC

This project follows in the footsteps of the Hammonator and Hammonator 2RVT organ amplifier to guitar amplifier conversion projects. A variety of Hammond tube amps are available on eBay for reasonable prices and they make a good platform for a guitar amplifier project. The Hammond AO-43 chassis is a prime candidate for conversion, it is large enough to build a full-featured amp with reverb and other effects and has a bare side that can hold many knobs and jacks. This amp has undergone a number of design changes since the original version was published. A second copy of the amp was constructed and the reverb driver tube was changed from a 6SN7 to a more period-correct 6FQ7/6CG7. The reverb driver circuitry was changed to include a Reverb Send control, this gives the amp a much wider variety of reverb sounds. The volume and reverb return controls have been wired in a mixer configuration which is somewhat unusual for amp designs. This makes it possible to listen to the reverb channel by itself or to have a mix with very heavy reverb. The vibrato circuit was also rebiased to produce a more intense effect. I liked the rev 2 modifications enough that I applied them to the original amp. The output stage of this amplifier uses 6BQ5/EL34 pentodes wired in a cathode-biased push-pull configuration, audio power output is around 15W. In the Hammonator project, almost all of the original circuitry was replaced. In this amp, most of the original power amp circuitry was reused. It is important to replace all of the electrolytic capacitors with new parts or bridge new capacitors across the old ones since the original capacitors have probably dried up and become lower in value. All of the resistors should be checked to verify the correct value, old resistors that are run hot tend to go up in value and should be replaced. The vibrato is somewhat subtle when the amp is played by itself. To get the best vibrato effect, a second amplifier should be plugged into Guitar Input 2 to tap into the input signal. The resulting stereo signal moves around the room in a manner that sounds a lot like a rotating Leslie speaker. Beware, once you get used to playing through a stereo setup all other amps will sound flat. One could consider this to be a left-handed amp, the signal path and knobs are mostly right to left. The chassis tube layout made this necessary.



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