Hammond L100 AO-43 amp project help?

For those building and repairing amps on their own. Learna and share ideas.

Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Fri Sep 18, 2015 5:16 pm

Here's a URL to a slideshow of the Organ Donor build-in-process photos.

Build photos slideshow
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After I had the full features of the amp working, I gutted everything and started from scratch using my schematic and layout drawings. I had created a modified layout that used a couple of vintage turret boards I found online. Starting over completely served as a good test of the layout and schematics. It worked like a champ and using the turret board rather than the original islet board allowed more components to be relocated from "space" onto a board. It also allow me to replace all the tube sockets with new, etc, etc.

Chassis Layout using a Turret Board
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Also isolated the magic eye tube circuits to their own boards which are then mounted within the amp cabinet adjacent to the magic eye tube each services. Here's the layout for each.

Magic Eye Board Layouts
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It still isn't as pretty inside as so much of what I see in other posts on this forum...I need to go through it again now and make the wiring more orderly. Maybe this winter...

Thanks again for the help of the forum members.
Last edited by housekustoms on Tue Dec 15, 2015 9:20 pm, edited 3 times in total.
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Re: Hammond L100 AO-43 amp project help?

Postby Unit_1 on Thu Nov 05, 2015 2:41 am

So I scored a ao43 amp off of eBay for $65 + 25 ship and it came with all the glass **FROM HOLLAND** -- the 2 EL84 and the 2 12ax7's test LIKE NEW and all the markings are in mint condition, no fading, no nothing!

muah haa haa haa haa haaaaaaaaaa

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Re: Hammond L100 AO-43 amp project help?

Postby ThisLifeILead on Thu Nov 05, 2015 8:36 pm

i built an AA1164 black face princeton reverb with the AO43 iron/tubes. Just phenomenal sounds it produces. Thats a great score Unit_1!
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Fri Nov 13, 2015 2:55 am

I never posted the chassis layouts for the 2 variants of the Hammond Vibrato chassis.

Hammond AO-41 Vibrato Chassis Layout
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Hammond AO-47 Vibrato Chassis Layout
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Re: Hammond L100 AO-43 amp project help?

Postby nlevesque on Mon Jun 06, 2016 1:24 am

i must say, what you've done is beauty. just acquired L-100 innards myself, and stumbled on your posts. your detailed postings are much appreciated, sir, and can't wait to get started. :cheers:
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Re: Hammond L100 AO-43 amp project help?

Postby Dech92 on Sat Dec 03, 2016 1:23 am

Housekustoms and all that help you design this amp, thank you very much.
Great build, far more than any other I have seen on line.
I am making one myself and lucky for me you did all the work.
I am great at reading schematics and building amps but I am no electrical engineer. So thank you again and to all that helped.
I also have another AO-43 but to this one I am going to make it hifi by removing the 12BH7 tube and everything related to the reverb.
Remove everything from R304 to R313 on the Original L-100 AO-43 Amplifier schematic he poster above his Organ Donor 18 schematic
Just not totally sure if I will have to change any values or maybe make first tube a 12au7 ?
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Fri Mar 03, 2017 9:50 pm

Thank you and please share your build and any changes you might make :D
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Re: Hammond L100 AO-43 amp project help?

Postby Fizzer07 on Wed Sep 20, 2017 5:49 pm

Question from an ignorant hack-
In the ao-47, when installing the "rate" pot, do you leave the existing resistors there or remove them?
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Fri Sep 22, 2017 3:07 pm

Question from an ignorant hack-
In the ao-47, when installing the "rate" pot, do you leave the existing resistors there or remove them?


The 470K resister R126 in the original schematic was replaced by a 2M linear taper pot.
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Re: Hammond L100 AO-43 amp project help?

Postby Fizzer07 on Sat Sep 23, 2017 2:12 pm

Great, I'll try it. Thanks to all for all the work you've done and advice you've given on this project, and for sharing it!
I made an amp with the AO-43 and AO-47, reverb tank, original 2x12" speakers, and the organ switches for controlling the reverb and vibrato. It'll be great to have an adjustable rate for the vibrato. This amp takes pedals very well and has great reverb and vibrato!
All I did was plug everything together with no circuit modifications, and mount everything into a homemade cabinet.
I'll post some pics soon.
I couldn't get the preamp unit to work at all. It would be nice to have a little more drive/ gain without pedals. Single coils don't crunch at all and my strat with a dimarzio super distortion pickup only starts to break up if you pick / strum hard.
Has anyone incorporated the preamp / percussion amp into a guitar amp?
Again, thanks to all.
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Mon Oct 09, 2017 5:55 pm

Please post pictures of your amp.
It would be nice to have a little more drive/ gain without pedals. Single coils don't crunch at all and my strat with a dimarzio super distortion pickup only starts to break up if you pick / strum hard.

The pre-amp chassis was of no real value given the mods made in adding the control pots. ;-) Additional gain and effects were a part of those changes.
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