Scored a Hammond AO-47 vibrato amplifier to make into a standalone unit.

[Rambozo96]

Despite this being a popular conversion the AO-47 vibrato amp seems to be still fairly inexpensive on reverb and eBay. Sluckey has a good write up on how to go about converting these into a standalone vibrato/phaser unit. In many ways it’s a precursor to the phaser pedals of the 70’s onwards. In fact any phaser can be converted into a pitch shifting vibrato by simply killing the dry signal side. After confirming that it works I’ll probably throw it all in a 1U rack chassis or perhaps gut a busted mixer head and throw it in that. I’m hoping to be able to reuse the original LFO as even though it appears to be at a fixed rate looking at phase shift oscillators in some tube tremolo units and the service note on the Hammond schematic notating one of the resistors is factory selected to achieve about 7 cycles per second should tell me where to tack on a speed pot. On Slucky’s write up he mentioned using a Fender LFO as opposed to the stock Hammond LFO and another online schematic leaves it up to you to choose an LFO for the unit which makes me wonder if the LFO doesn’t reside in the vibrato amp chassis itself even though the fact that the 7247 tube on the chassis would suggest that at least some of it if not all is present within the chassis. Anyway it’s to arrive tomorrow and updates will follow.

Here’s the link to Slucky’s write up about the conversion. https://sluckeyamps.com/warbler/warbler_rev2.htm

 

[Canard]

I am impressed with people who do this sort of stuff with nonchalance, even with careful nonchalance. Things with tubes and big capacitors scare me. I wear rubber gloves. I have capacitor discharge resistors. Still scared.

My brother has a screwdriver mounted on a plaque above his workbench. When tired once while working on an old school CRT colour TV, he unthinkingly picked up a non-insulated screwdriver and set to work. The fairly hefty shaft on the screwdriver is now arc'd through to the extent that if you held it up in a stiff breeze, the shaft would bend or break. The screwdriver now serves a cautionary momento mori.