• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

1955 Hammond Organ Tube Amp

Torren61

Member
2013-03-29 11:02 pm
Hello. New guy here.

I procured a free Craigslist 1955 Hammond organ recently. Here is a picture of the amp.

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I'd love to make a guitar amp head from the parts but i am clueless on how to do it. Previously, I've built two heads from kits but these came with instructions and a parts list.

Would any of you kind gentlemen have instructions and a parts list on how to do a conversion? I think I'd prefer a Fender type head but I'd love to hear some suggestions.

The rectifier tube is a 5U4GA

AE7567D7-B25A-4081-96D5-52BA35E6A0B1-6817-000004A0E0C36071_zps1224ee6f.jpg


The organ came with a pleasant surprise. I found a smooth plate Telefunken 12AX7 tube. Made in West Germany.

Thanks in advance!
 
This really belongs on the Instruments and Amps "board" and I'm sure the moderators will move the thread. Still, you have plenty to work with. What are the O/P tubes? I'm guessing 6V6s. Should that be the case, I see a Fender design knockoff in your future.

Rectifier tubes have long service lives. When the GE 5U4GA "gives up the ghost", install an ElectroHarmonix (EH) 5U4GB. The 'GB has slightly larger cojones than the 'GA. ;)
 

Torren61

Member
2013-03-29 11:02 pm
This really belongs on the Instruments and Amps "board" and I'm sure the moderators will move the thread. Still, you have plenty to work with. What are the O/P tubes? I'm guessing 6V6s. Should that be the case, I see a Fender design knockoff in your future.

Rectifier tubes have long service lives. When the GE 5U4GA "gives up the ghost", install an ElectroHarmonix (EH) 5U4GB. The 'GB has slightly larger cojones than the 'GA. ;)

Hey thanks! Yes, please, mods. Would you move?
 
Look here for 1 of Leo's "Deluxe" schematics. That should be a decent starting point for you.

BTW, the 7025 is a 12AX7 that contains a spiral wound, hum bucking heater. Unfortunately, no low microphonic tube is currently being made with that feature. The easy solution is a DC heater supply for a 12AX7 at the amp's front end. The current production Sovtek 12AX7LPS is a genuine 7025 equivalent, but its long plate construction makes it microphonic prone, in guitar amp service.
 

Torren61

Member
2013-03-29 11:02 pm
Look here for 1 of Leo's "Deluxe" schematics. That should be a decent starting point for you.

BTW, the 7025 is a 12AX7 that contains a spiral wound, hum bucking heater. Unfortunately, no low microphonic tube is currently being made with that feature. The easy solution is a DC heater supply for a 12AX7 at the amp's front end. The current production Sovtek 12AX7LPS is a genuine 7025 equivalent, but its long plate construction makes it microphonic prone, in guitar amp service.

Thanks Eli. I'm, again, clueless on how to read a schematic. I'm good with pictures, though. :D
 
Yow,
Don't kill a Hammond for the amplifier. If you want a Fender type head, build that. There's a good bit of stuff in that amplifier you'll just disconnect to make a guitar amp and at that point you'll have a 3 or 4 tube amplifier not really suited to what you want. Is that an A-100? It's pretty much the same as a B3. A better project might be to 'chop' it to make a lighter B3. That's a non-electronic project. Mostly taking everything out of the mahogany case to make it lighter. Dr. Lonnie Smith travels with one, with a Lestlie speaker, all out of 1/4" plywood on wheels-nice. A working Hammond would be way better than a fubar guitar amp. The A-100 is a pretty desirable piece: A-100

Cheers,
Marshall
 

Torren61

Member
2013-03-29 11:02 pm
Yow,
Don't kill a Hammond for the amplifier. If you want a Fender type head, build that. There's a good bit of stuff in that amplifier you'll just disconnect to make a guitar amp and at that point you'll have a 3 or 4 tube amplifier not really suited to what you want. Is that an A-100? It's pretty much the same as a B3. A better project might be to 'chop' it to make a lighter B3. That's a non-electronic project. Mostly taking everything out of the mahogany case to make it lighter. Dr. Lonnie Smith travels with one, with a Lestlie speaker, all out of 1/4" plywood on wheels-nice. A working Hammond would be way better than a fubar guitar amp. The A-100 is a pretty desirable piece: A-100

Cheers,
Marshall

Come get it and bring a low watt tube head with you for trade. :D In fact, I have a deal for you. You come here and help me load it. I'll drive it to your house and help you get it inside. You swap me a cool low watt tube head. I foot the bill for my diesel to your house. Done.
 
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I picked up three of these M3s last year for free on CL. The first thing you need to do is read ALOT. Learn to read a schematic, then remove everything but the heater wiring and build whatever you can. I would start with a simple Fender design. I like the 5E3 personally. Keep in mind tube amps carry enough voltage to kill you even when not plugged in. Does the organ have a field coil speaker?
 
I feel a bit better. M's were sold crippled for "organists" that play with one hand. Scrapping an A or a CV or BV is a travesty, the tone generators were built to last 100 years with a little oil yearly.
The schematic diagrams are on captain-foldback.com.
The main thing you have to do to make a guitar amp is bypass the variable capacitance volume control. You can also monkey with the first stage gain resistors to get foot pedal controlled gain for that guitar "crunch" that burns up tubes. See organforum.com. I don't see the point of taking out a lot of parts to make it a Marshall. Marshalls were sold to a price point, Hammond owned the organ market in 1955 so they built it the way you would want if you were making a large profit. The vibrato circuit (2nd input) may be redundant for a guitar, but some people hook them up in front of the original amp stage for more gain to get crunch. Standard signal in is 25 mvac.
Personally I'm fiddling with speed control on a Hammond so I can bend pitch like Beck on guitar. Only six notes played at a time, guitar is so simplistic. I play 10 tones simultaneously sometimes, sometimes 12. A simple envelope generator/mixer can give Hammond tones as much twang as anybody wants.
 
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Back in the day I had an M3 (plus a Leslie), still miss it. It was awesome.

"Known for its classic tone wheel sound, many experts consider the Hammond M3 organ to be the closest organ in the spinet category to achieve the B3 sound.

Nicknamed the "Baby B", the Hammond M3 organ is very much like the B3 internally."