Hammond AO-29 conversion

[kc7fys]

Also building a guitar amp from the AO-29

I'm monitoring this thread, looking for active past/present builders using this chassis. I have three of them also, so can exercise different options. Photos of your finished work, those who did it with this amp? Thank you,
Jonathan

 

[scrimpu]

Here's a 5E3 and a Marshall style amp I have built with the AO-29.

 

[frpax]

Thread resurrection time!

One of my neighbors threw away an old (1956/7) Hammond M3! So I salvaged a bunch of stuff:

• The AO-29 amp, which looks like it is in good shape, but I don't know if it even works.
• Original Rola speaker dated to the last week of August, 1956 (with original grill cloth).
• I managed to get a lot of the organ wooden parts, that I plan on using for a cabinet.
• SCADS of the original push-back wire.

So, my plan (obviously) is to convert it into a guitar amp.

I have never attempted to build an amp before, but I have built and wired up several "partscasters" and I do a decent job soldering. I can follow a schematic somewhat. I'm certainly not afraid to jump into this with both feet! I have a pretty strong adventurous streak in me!

So, I'm not totally sure what I want to turn it into (circuit-wise) or just leave as much of it as-is as possible so that it is it's own thing. Recommendations are VERY welcome!

I have read this thread and someone said that there is a lot in this amp that is totally unnecessary for a guitar amp. I certainly does look more complex than the vintage Fender & Marshall amps (and clones) that I am familiar with.

So, ANY comments, suggestions, opinions & recommendations are highly welcomed!

Thanks!

 

[boobtube]

Did you save the smaller reverb amp? There should have been either an AO-35, AO-44 or another one I don't remember right now. Those two I mentioned are the easiest to convert to guitar amps. If the organ is still there, go get that other amp. The AO-29 has a LOT of extra tone-shaping/shifting circuitry at the opposite end of the power tranny. Look at scrimpu's pictures just above your post. See all the space at the left that's empty? That's where all that stuff is at and should be eliminated. And the schematic for those two reverb amps I mentioned are far easier to read. Unless of course you plan on gutting yours and starting from scratch. But using that main chassis leaves you an extra 4-5 inches of unused space at that end. Or did you not have the reverb installed. I just looked up the info and found there was both reverb and non-reverb models for the M3. I thought all M3s has reverb.

 

[boobtube]

Here's a pic of one with the reverb. It's the small amp on the right. That one is the AO-35 and there's a wealth of info on the net for converting one of those. Also much info for the AO-44 as well.

 

[frpax]

Here's a pic of one with the reverb. It's the small amp on the right. That one is the AO-35 and there's a wealth of info on the net for converting one of those. Also much info for the AO-44 as well.

boobtube,
the organ did not have that reverb amp, otherwise I would have grabbed it as well.

 

[frpax]

boobtube,
the organ did not have that reverb amp, otherwise I would have grabbed it as well.

Let me be more clear. The organ did not have a reverb amp, nor did it look like there was ever one installed. There were no loose wires hanging about; there were no empty screw holes that would indicate that there once was a reverb amp.
The organ was made at either the tail end of 1956 or the very beginning of 1957. It was a Model M3-A1. Perhaps reverb was a feature that later M3's had?

Somebody made off with all the rest of it anyway, which was essentially just the keyboard and pulls section and the bass pedals and the scraps of wood that were attached to them.

 

[boobtube]

I figured you would have grabbed that reverb amp but wanted to make sure you knew about it just in case.

Here's a link for a guy who rebuilt one to replace in an organ but there's a good schematic on the site that has all of what's on the chassis highlighted in yellow: http://www.stefanv.com/electronics/hammond_ao29_overhaul.html This will help if you want to keep most of what's there already and mod it for guitar.

Many guys will just make this into a Fender Tweed 5E3 Deluxe if you want to gut it and start from scratch and keep the trannies. Since it uses 6V6s, it's good for that amp. Here's a link to that schematic and layout: http://el34world.com/charts/Schematics/files/fender/Fender_deluxe_5e3_schem.pdf

You can also turn it into a low wattage Plexi Marshall. Here's a link courtesy of Mark Huss. He really knows his stuff, so this should sound pretty good: The Plexi 6V6

So this gives you three alternatives but this isn't such a great candidate to just mod or for it to be your first amp. There's a lot of demo to do to get it ready for rebuilding.
Also, there's tons of good info on the AX84 site. It might be good to look there for an easier amp to start with and to read the High Voltage Safety link since this is your first build: http://www.ax84.com/

 

[frpax]

Thanks, boobtube.

Although this is my first official amp "build", I have done some amp repairs before. So I'm not a total noob!

 

[boobtube]

That's good to hear. it's always nice to know that someone relatively new to this will stay safe. That's the most important thing!

 

[God of keys]

there are mods to get a crown jack out on the expresion pedal and you could *** apot in lie w/thea.

 

[DavebF]

Anyone ever find any specs on T-5 and/or T-6? If possible I'd love to use one of those to drive a reverb tank.

 

[DavebF]

You can look through Mr. Hanert's 1950 patent for the expression control (#2,646,468) it's avalible on the interenet, he gives the minimum capcitance as 25 micro-microfarads.