Alright so I've been reading and reading and reading a lot of the threads about doing a hammond conversion, and I am at the very beginning of my own. I bought an AO-29 with all working tubes on eBay for $60 total. Here are a few pics. My plan is to gut it out and use the chassis, PT, OT and tubes to build a princeton reverb. I've been going off of the Weber 6A14 BOM and I plan using the 6A14 schematic as well.
Does anyone have any good experience with this build? I know I'm probably going to have to bring down the voltages from the PT and I've read several things about using a choke, a resistor or the zener. Can someone suggest what they have used and how well it worked? The AO-29 that I have is also one of the field coil models.
Another Hammond Build
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Another Hammond Build
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For God did not send his Son into the world to condemn the world, but in order that the world might be saved through him. John 3:17
Re: Another Hammond Build
According to the schematic http://hammondb3organ.net/schematics/ha ... -29-fc.pdf the PT is 380-0-380 and is rated 140mA on the HT secondary.
Choke input will probably get you there, read: http://www.aikenamps.com/index.php/chokes-explained but may have an impact on tone (good or bad is up to your ears.)
More geeky stuff with formulae: http://www.lh-electric.net/tutorials/psupply.html see fig.4 half way down.
Choke input will probably get you there, read: http://www.aikenamps.com/index.php/chokes-explained but may have an impact on tone (good or bad is up to your ears.)
More geeky stuff with formulae: http://www.lh-electric.net/tutorials/psupply.html see fig.4 half way down.
Re: Another Hammond Build
I've done two of these AO-29 conversions so far. I built a Plexi6v6 with the AO-29 with silver power transformer and my plate voltage came in at 391 with bias adjusted properly. It uses a Hammond 5u4 for the rectifier, and has a choke where Mark shows it on the schematic.
Your chassis has the black power transformer which is smaller, and if it's like mine, lower voltage. I used an AO-29 with a black transformer for my Tweed Deluxe clone, and my plate voltages came in at 356 with bias set up right. That one uses a NOS 5y3 rectifier, and no voltage lowering device that's not on the Tweed Deluxe schematic. No choke, zener, resistor, nothing. I tried 5u4, 5y3 (both NOS and new Soviet) and 5R4 and the NOS 5y3 rendered the lowest voltage, so I went with it and the combination works perfectly. It's the best amp I have.
I would not hesitate to build a Princeton Reverb using the black transformer. In fact, that's a really good idea - as soon as I finish this Ultra Champ on my bench.
Your chassis has the black power transformer which is smaller, and if it's like mine, lower voltage. I used an AO-29 with a black transformer for my Tweed Deluxe clone, and my plate voltages came in at 356 with bias set up right. That one uses a NOS 5y3 rectifier, and no voltage lowering device that's not on the Tweed Deluxe schematic. No choke, zener, resistor, nothing. I tried 5u4, 5y3 (both NOS and new Soviet) and 5R4 and the NOS 5y3 rendered the lowest voltage, so I went with it and the combination works perfectly. It's the best amp I have.
I would not hesitate to build a Princeton Reverb using the black transformer. In fact, that's a really good idea - as soon as I finish this Ultra Champ on my bench.
Thanks,
Roger
Roger
Re: Another Hammond Build
This weekend I'll check and see what my actual voltage coming out of the PT is. Hopefully nothing extra will be needed. I'm planning to use the 5U4GB that came with the amp as my recto.
Any experience with the field coil OT? It says to use with an 8 ohm speaker but also has two 100 ohm resistors on the ao-29 schematic. Do i need to use a power resistor or choke to accommodate this impedance? Also still not quite sure how to calculate what speakers I can use. Was planning running 2x10 with it.
Any experience with the field coil OT? It says to use with an 8 ohm speaker but also has two 100 ohm resistors on the ao-29 schematic. Do i need to use a power resistor or choke to accommodate this impedance? Also still not quite sure how to calculate what speakers I can use. Was planning running 2x10 with it.
For God did not send his Son into the world to condemn the world, but in order that the world might be saved through him. John 3:17
Re: Another Hammond Build
No experience with the field coil OT but I can tell you that my black transformer AO-29 was a -13 just like yours, and I used the OT from it in my Tweed Deluxe without modifying the circuit in the 5e3 schematic in any way. I don't think mine is field coil. What number is on the metal cover over your OT?
On the AO_29 schematic I have, it looks like those two 100 ohm resistors set up the feedback to the amp at V4B, which won't necessarily apply in your Princeton Reverb. The Princeton Reverb's (aa1164 schematic) feedback circuit will be established with a 2.7k ohm resistor from one leg of the OT back to the cathode circuit of the amp's 3rd stage, right after the reverb recovery tube. If I build one, I'll put a 1k resistor and maybe a 5k pot in place of the 2.7k resistor and call it "Presence".
On the AO_29 schematic I have, it looks like those two 100 ohm resistors set up the feedback to the amp at V4B, which won't necessarily apply in your Princeton Reverb. The Princeton Reverb's (aa1164 schematic) feedback circuit will be established with a 2.7k ohm resistor from one leg of the OT back to the cathode circuit of the amp's 3rd stage, right after the reverb recovery tube. If I build one, I'll put a 1k resistor and maybe a 5k pot in place of the 2.7k resistor and call it "Presence".
Thanks,
Roger
Roger
Re: Another Hammond Build
From what I've seen there are some ao-29 that have the pm and some have field coil. I don't know if the -13 specifies the type. My it is A024924 0
524 65 17.
524 65 17.
For God did not send his Son into the world to condemn the world, but in order that the world might be saved through him. John 3:17
Re: Another Hammond Build
I also have the AO 24924 0 output transformer in my Tweed Deluxe clone. Works perfectly with no modifications. Drives an 8 ohm Fender speaker and sounds terrific. If I were building a Princeton Reverb, I would not hesitate to use that transformer.
If you go with 2x10s, get either 4 ohm speakers and wire them in series, or 16 ohm speakers and wire them in parallel.
If you go with 2x10s, get either 4 ohm speakers and wire them in series, or 16 ohm speakers and wire them in parallel.
Thanks,
Roger
Roger
Re: Another Hammond Build
Okay awesome, that will be the plan. Did you mess around with any of the other transformers inside of the chassis? At least that's what they look like from the outside. Looks like a couple smaller transformers maybe? Just wondering if that's what they are, would they be good for anything.
For God did not send his Son into the world to condemn the world, but in order that the world might be saved through him. John 3:17
Re: Another Hammond Build
Okay, so after just using my brain and deciding to look at the schematic, I see that there are three transformers used for the percussion amplifier. I'm trying to find some information about them to see if possibly I could use one for my reverb transformer. Someone mentioned this possibility here http://www.ax84.com/bbs/dm.php?thread=293769.
If anyone has any information on the T4, T5 or T6 in this schematic it would be greatly appreciated.
http://captain-foldback.com/Hammond_sub ... 3_late.gif
If anyone has any information on the T4, T5 or T6 in this schematic it would be greatly appreciated.
http://captain-foldback.com/Hammond_sub ... 3_late.gif
For God did not send his Son into the world to condemn the world, but in order that the world might be saved through him. John 3:17