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Old 29th March 2013, 11:11 PM   #1
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Default 1955 Hammond Organ Tube Amp

Hello. New guy here.

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

Click the image to open in full size.

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

Click the image to open in full size.

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

Thanks in advance!
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Old 29th March 2013, 11:35 PM   #2
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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.
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Old 29th March 2013, 11:50 PM   #3
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Originally Posted by Eli Duttman View Post
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?
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Old 30th March 2013, 12:14 AM   #4
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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.
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Old 30th March 2013, 12:36 AM   #5
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Originally Posted by Eli Duttman View Post
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.
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Old 30th March 2013, 12:52 AM   #6
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Quote:
I'm, again, clueless on how to read a schematic.
If you are going to build, modify, or repair stuff (tubed or SS), schematic reading is a skill you MUST acquire. Run a Google search for NEETS. NEETS is U.S. Navy electronic training material available on the WWW, gratis.
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Old 30th March 2013, 01:23 AM   #7
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Originally Posted by Eli Duttman View Post
If you are going to build, modify, or repair stuff (tubed or SS), schematic reading is a skill you MUST acquire. Run a Google search for NEETS. NEETS is U.S. Navy electronic training material available on the WWW, gratis.
YOU are a great guy! Thanks again!
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Old 30th March 2013, 01:32 AM   #8
mlise is offline mlise  United States
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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
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Old 30th March 2013, 01:55 AM   #9
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what was the Hammond model ?
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Old 30th March 2013, 02:04 AM   #10
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Originally Posted by trobbins View Post
what was the Hammond model ?
1955 M3
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