Hammond AO-63 conversion

[jmccanna]

Hello,

Hmmmmm. I will give that a try tomorrow morning. I have a 12AX7 in there now. Thanks. I will take a look at the AC15 schematic too. I am grateful for the suggestion.

[sluckey]

Let me clarify... You can't just plug an EF86 into that V1 socket! You must remove the existing V1 circuit, rewire for the EF86 circuit, then plug in the EF86 tube. Sorry for any confusion. Look at page 2 of this pdf...

http://sluckeyamps.com/VAC15/Vox_AC15.pdf

You would need to build the circuit between the input jacks and the volume control.

[jmccanna]

Hi Sluckey,

Thanks for being so helpful and thoughtful. It has made this process immeasurably clearer, understandable and more fun. Actually, I understood that it was not a direct replacement and it got me thinking further about this. Like you have suggested, I am taking time thinking this through. I have been reviewing the AC15 schematics I found on the internet.

So, now I will build the preamp on the actual preamp chassis so I can have access to the tube sockets. That way if I redesign or add to the preamp circuit I will have it readily available. Since this is such a large amp I can build the case to incorporate the pre chassis too. Secondly, since I will be using an EF86, building it as a head unit rather than combo will isolate the EF86 from speaker vibrations a bit.

I want to keep things simple but open to I changes later. That said, the existing reverb tank is adequate but sort of one dimensional and not very controllable. I would like to have more control over it and am considering adding a dwell control to it. In your GemiVibe I see that you do not use the reverb amp at all but mix the reverb into the signal going to the main amp. Perhaps, I am being too possessive of continuing to use the reverb amp? I just really like the thought of it and it does sound good.

Thanks again.

[sluckey]

Perhaps, I am being too possessive of continuing to use the reverb amp? I just really like the thought of it and it does sound good.

That's a good argument for taking your time at this point. It is unique to have a completely separate amp for a reverb speaker. And the sound is nice. I have played with several different Hammond amps. One of them was an AO-44 reverb amp which is very similar to the AO-63 reverb amp. At one time I was using the AO-44 (with no mods) as a separate reverb amp. Didn't take too long for the uniqueness to wear off. It's a lot of extra hardware for a reverb sound that in the end, really doesn't sound any better than other quality reverb amps such as a Fender or Sunn or Ampeg or even a good reverb pedal. I think with some time you may come to that conclusion too, but since you have the opportunity, give it some time.

I also have quite a few other guitar amps so it was easy to patch several different preamps into the AO-63 power amp, totally bypassing that organ preamp. I replaced the "Brushes and Cymbals" phono jack with a 1/4" phone jack connected directly to the junction of R313 and R314. This allowed me to connect various preamps directly to V302A. The Ampeg preamp was exactly what I was hoping for. The Fender AB763 and Sunn Sceptre were close runner-ups. It didn't take long to decide to replace the V1 circuit with the Ampeg preamp circuit. The AO-63 sounded great. It was several months later that I decided to experiment with the reverb section. And finally, adding tremolo was a no brainer.

If you have some other amps you may consider patching those preamps into the AO-63 as I described above. Even plugging your Akai directly into V302A rather than into the organ preamp is worth trying.

[jmccanna]

Query: Since this project and the next one with a Baldwin tube amp is in the offing perhaps it is time for me to invest in some tube circuit simulation software. Would you have a recommendation? The schematics you created are real clean and easy to read.

James

[pompeiisneaks]

I think the only simulation software I've seen people use are variants of spice. LTSpice, etc. I don't know much about it myself and only played with it once and found the learning curve something I wasn't interested in.

~Phil

[sluckey]

I have no need for circuit simulation software. I plagiarize. Then I use Visio to draw schematics and layouts.

[jmccanna]

I think the only simulation software I've seen people use are variants of spice. LTSpice, etc. I don't know much about it myself and only played with it once and found the learning curve something I wasn't interested in.

~Phil

Phil,

Thanks I hear that. There are little enough unused neurons left in my brain. I have tried and end up thinking why? I am up here in Kingston, WA. Where are you if I may ask?

Thanks,

James

[jmccanna]

I have no need for circuit simulation software. I plagiarize. Then I use Visio to draw schematics and layouts.

Plagiarizing works too! I have to check and see if I have Visio. It would certainly help me visualize what I need to do to get where I want to be.

Thanks, off to client meetings.

James

[pompeiisneaks]

I think the only simulation software I've seen people use are variants of spice. LTSpice, etc. I don't know much about it myself and only played with it once and found the learning curve something I wasn't interested in.

~Phil

Phil,

Thanks I hear that. There are little enough unused neurons left in my brain. I have tried and end up thinking why? I am up here in Kingston, WA. Where are you if I may ask?

Thanks,

James

I live in Redmond, just across the sound from you.

~Phil

[jmccanna]

Phil,

Pretty small world I would say. I don't get on that side too much of late though my wife and I did catch a show at the Teatro ZinZanni at Marymoor Park last month.

This amp has been a fun project. I was scared of it for awhile due to the complexity of it but once I got started with Sluckey's excellent help it is really coming together.

[jmccanna]

Well,

I look through the local CL posts here in Kitsap. I have been thinking of putting an EF86 in the preamp. Well, lookee here!

https://seattle.craigslist.org/tac/msg/ ... 66254.html

[pompeiisneaks]

Phil,

Pretty small world I would say. I don't get on that side too much of late though my wife and I did catch a show at the Teatro ZinZanni at Marymoor Park last month.

This amp has been a fun project. I was scared of it for awhile due to the complexity of it but once I got started with Sluckey's excellent help it is really coming together.

Cool, I live like less than a mile from marymoor, walk the dogs there all the time

~Phil

[sluckey]

Any ideas coming together?

[jmccanna]

Hi,

I do have ideas but have been caught up in some family emergencies. I am thinking of using the existing preamp chassis. It has four 12AX7 sockets and two EF86 sockets. So, I was thinking of having one preamp to emulate the circuitry in the Akai (the sound I love) and the other to use the Vox AC15 preamp circuit without the tremolo - both of which connect to the power amp chassis. Separate inputs for each. The question I have is to design it so one side in use cancels the other side.

I have not had the time or energy to figure it all out yet but am slowly working on putting a schematic together for comments here before I do.

Kind of like that custom amp I linked to earlier. It had two "voices" on the preamp powered by a different Hammond organ amplifier.