Ultimate Hammond Conversions thread

[Kczech]

I spent 5 mins going over the chasis looking for a AO# and couldn't locate anything. The underside has 13 written with a green marker.

[sluckey]

I've never seen that one. The PT and OT are the same as found on the AO-29-13.

[thetragichero]

measured and calculated these awhile back
ao-24924 output transformer 7k4:8
ao-24110 power transformer
red-red/yellow-red 350v-0-350v
brown-green-brown 6.3vct
yellow 5v (3A since this runs a 5u4)

shame didn't come with the ao-43 chassis that was likely in the organ with it. two ecl86 tubes are fun to mess with (especially if you add another 12ax7)

[sluckey]

shame didn't come with the ao-43 chassis that was likely in the organ with it. two ecl86 tubes are fun to mess with (especially if you add another 12ax7)

The AO-43 uses 6BQ5/EL84. The PT is AO-24157-1 and OT is AO-24158-0.

The AO-44 uses ECL86/6GW8. The PT is AO-24956-1 and the OT is AO-24158-0 (same as AO-43).

[thetragichero]

meant 44, typed 43. hammond's numbering convention seems about as useful as marshall's

[dragonbat13]

Amp and preamp out of L74 Baldwin. Have all Baldwin tubes. All kinds of extras. Fused leads off power transformer. Flyback diodes on the OT.

[ok_state_blues]

Hammond S-1 to 5E4A. Thanks for all the knowledge on here. I didn't want this sticky to die

[Colossal]

Hammond S-1 to 5E4A. Thanks for all the knowledge on here. I didn't want this sticky to die

Sweet amp, man. I have heard some seriously good conversions using Old Hammond iron.

[ok_state_blues]

Hammond S-1 to 5E4A. Thanks for all the knowledge on here. I didn't want this sticky to die

Sweet amp, man. I have heard some seriously good conversions using Old Hammond iron.

Yes it works great as long as you can tame the voltage. Captain foldback has been a very valuable resource. Now I know what to do with the field coil PT's!

[ok_state_blues]

Hammond AO-14 to Matchless Lightning.

[Cartman]

Have any of you Hammond builders run these amps with a mis-matched speaker load? If so, were there any negative effects noticed? I have two AO-43 and one AO-35 converted to circuits for guitar, and I always use a 8 ohm speaker load. Just wondering if these would be fine with a 4 ohm or 16 ohm speaker load. I know that Hammond iron is known to be pretty robust.

[sluckey]

I have run the AO-43 OTs with 8Ω and 4Ω speaker loads with no ill effects.

[Cartman]

FWIW, I tried both of my AO-43 amps through 8 Ohm and 4 Ohm cabs. A single speaker at 8 Ohms and a pair of the same speakers in parallel at 4 Ohms. They both sounded fine with either load, and the transformers did not get hot. I did notice a slight drop in volume at 4 Ohms. I guess that is to be expected if the OT is designed for 8 Ohm load.

[maxkracht]

Here's my latest Hammond conversion. AO-43 to something resembling a modified Princeton reverb with a cathode biased 7189 back end.

 I lifted a transformerless reverb driver from Merlin’s site and the LND150 recovery stage (I think) from a fx loop schematic? Cant quite remember where I stole it from or who to credit. The reverb switch is backwards, down being on. Couldn’t figure out how to easily reverse it without making the wiring more of a headache. There’s a foot switch anyway… TMB tone stack, no negative feedback, Vox cut control (sparkle). Planning another with a master volume, neg feedback, and no cut control.



I’m pretty happy with the layout, aside from the upside down reverb switch. Kept the original PWR and REVERB SW. markings/functions. Used every original eyelet and tag strip (excluding grounds) and only one added turret attached to the treble pot. I kept the reverb choke in place and added another dropping resistor before it for good measure. The amp has a very low noise floor and sounds pretty good to me. Reverb is very surfy. I would be happy to hear suggestions for improvements if anyone has them. Not all of the values on the layout are exactly what I ended up with. I tend to change my mind on details mid build.
 
I made a time-lapse video of this and a handful of other hammond conversions I’ve done this year if anyone is interested.



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hammond ao-43 layout.jpg

[dragonbat13]

That's a very nice conversion. From what I've heard conversions are difficult. Yours makes it look even more challenging. If I could ever get caught up I want to mess with my Baldwin.