Hammond AO-63 conversion

[jmccanna]

Update: If anyone is interested after my epic, far too long string of posts! Disregard the circuit I described in the last post. I have gone simple and have just an EF86 tube driving the pretty much stock Hammond organ amp. It sounds the way I want it to. I will be adding a dwell circuit and a one-knob tone circuit to it to tame some of the highs a bit. I have attached a .mp3 soundclip of what it sound like. I recorded it with a Zoom H2 about 3 feet from the speaker cab. No processing other than converting to .mp3 (which I hate to do).

Edit: Phil adding a link to the mp3:



Thanks,

James

[pompeiisneaks]

Sounds great! Very clear sound, love it!

~Phil

[jmccanna]

Sounds great! Very clear sound, love it!

~Phil

I cannot tell you how affirming your comment is! I have struggled with this a lot - mostly because of my learning curve - but a struggle nonetheless. Thanks!

[jmccanna]

I have several sockets left on the preamp board for my amp. At present I am using just one EF86 that goes through one 22k potentiometer to the amp. That is my only volume control. Sounds great but is not very flexible. To get overdrive tone I have to turn it up very loud.

So, I had this thought. What if I connected a 12AX7 and the EF86 at the same time to the guitar input and then send each tube output through a coupling cap to a stereo potentiometer that then goes to the existing potentiometer that controls the amp? Full left would be the 12A and full right would be the EF86. In the middle would be a mix of the two.

I know this is done inside guitars to blend signal from different pickups but this would be working in a higher voltage arena.

Would this work? I am likely missing something but thought I would ask. I will await a response before I try it.

[jmccanna]

Hello all,

Meet MyHammy! I have solved most of the problems, there is still a little bit of a hum but it is tolerable. I made a lot of changes to simplify. I ditched trying to use the EF86 on a separate board because it was too complicated with lots of wires running to and fro and it gave too much gain (as I recall Sluckey warning me about early on)

So, I wired it up for a preamp circuit run by a 12AU7 with a pot in between the halves for a gain/volume control. I tapped off of the second plate signal for that to the reverb driver circuit (a 7247). I put a dwell control in between the two halves of the 7247 before the reverb tank and then a pot between the reverb return send and the reverb amplifier circuit. I had quite a bit of hum until I put in the last pot which has calmed it down a lot. The sound is very good and it gets loud.

I can easily overdrive the circuit but it is very clean at lower volumes. The reverb can go for days and get all too reverby if I want. I can fine-tune it with the dwell and volume controls.

Here is a picture. Later, I will capture some sound samples and send those along too. I managed to preserve the original power switch. I left the round connector in place (but disconnected) in case I ever come across a leslie to play with.

Thanks for all the suggestions and help and patience and tolerance. It feels great to have saved this from the landfill. It is very nearly as old as I am.

James

[jmccanna]

Forgot to mention I mounted the reverb tank underneath the board on which the amp is mounted.

[xtian]

Forgot to mention I mounted the reverb tank underneath the board on which the amp is mounted.

A lot of hum can come from the reverb pan being too close to energy radiated by the power transformer.

[jmccanna]

Thanks. The tank is under a piece of 3/4" marine plywood and the amp is on top. Would that be too close?

[pompeiisneaks]

You can find out really quickly by moving the reverb pan a bit farther away. There's a reason fender puts them on the bottom of the combo. One in a head can be a nightmare. I had a really bad sounding hum in a head once that I found was caused by the reverb pan. I had to move it left and tilt it slightly off kilter to kill 'most' of the noise, but it still left a tiny bit, but it was enough to make the owner happy.

~Phil

[jmccanna]

Hey Phil! Thanks I will try that. A bit cumbersome to get under it now but it is worth a shot. It sounds really good. A lot has happened since I started on this and it is such a relief to get it to a playable spot. Now, tweaking is the goal.

[Mant]

What an enjoyable thread.

[James1972jvc]

Hey Phil! Thanks I will try that. A bit cumbersome to get under it now but it is worth a shot. It sounds really good. A lot has happened since I started on this and it is such a relief to get it to a playable spot. Now, tweaking is the goal.

Very neat thread @jmccanna ! How's this amp holding out for you? I have a spare AO-63 as well and am trying to decide what to do with it.

[sluckey]

Very neat thread @jmccanna ! How's this amp holding out for you? I have a spare AO-63 as well and am trying to decide what to do with it.

Take a look at my AO-63 conversion. Might give you some ideas.

https://sluckeyamps.com/hammond_2/hammond2.htm