Hammond AO-29 amp convert to Plexi 6V6?

[frpax]

Hello all!

I joined this forum, because there seems to be a wealth of knowledge here, and I definitely need help!

One of my neighbors threw away an old 1957 Hammond M3-A1 organ, so I (being the resourceful guy that I am) grabbed the AO-29 amp and the field coil speaker, as well as quite a bit of the organ's nice looking wood so I can make a cool cabinet for the amp. Recycling at its best!

I did get some help from a guy named Brad (aka the Guitologist on YouTube and Facebook, who is a great guy, btw) as he took a slightly later version of the AO-29 and converted it to guitar, but his did not have the field coil speaker. But, I managed to copy his schematic as best as I could, with the only real difference being the field coil stuff.

Now. Here's my problem. I'm not schooled enough to take a schematic and turn it into an actual physical layout. I can read the schematic OK...I know what all the symbols mean and stuff, but physically going from schematic to real item, I can't do. So this is where I need some help from you gurus.

Now I CAN read a layout or wiring diagram really well, something like this:



That's super easy for me to visualize and build.

So what I need is my schematic:



to be turned into a layout like above.
I would really like to utilize as much of the original Hammond parts as possible, to keep costs down and mojo factor up!
I plan on using the Hammond chassis and transfomers, tubes, sockets, and as many of the caps and resistors as possible.
Oh, forget the tremolo circuit. I decided I'd probably never use it. Instead, I want a tone stack that is Bass, Mids, & Treble, like Sluckey's Plexi 6V6.

Can anyone help me with this?

Any and all comments or suggestions are greatly appreciated!

[Paul1453]

Could you post some pictures of your actual gear you want to use?

Sluckey is an expert in these Hammond conversions.

I had some difficulty starting out, trying to reuse various chassis' and their previous layouts.

If you have problems working out your own layouts,
it might be best to use Doug's chassis and circuit board on your build.

You'll obviously use as many parts from the Hammond as you can,
and you will probably have a better chance of success using Doug's proven layout and board.

[frpax]

Could you post some pictures of your actual gear you want to use?

Sluckey is an expert in these Hammond conversions.

I had some difficulty starting out, trying to reuse various chassis' and their previous layouts.

If you have problems working out your own layouts,
it might be best to use Doug's chassis and circuit board on your build.

You'll obviously use as many parts from the Hammond as you can,
and you will probably have a better chance of success using Doug's proven layout and board.

Not a problem:










The big transformer is stamped AO-22111-1

The smaller one has AO-20936-3 on the top metal part and AO-20935-4 on the brown waxy paper stuff on the inside

My tube layout from L-R is:
V-11: 5U4
V-10: not using (6BA6 - I was going to use this as a tremolo circuit borrowed from a Silvertone 1482 schematic and use a 6AU6 in place of the 6BA6)
V-6: 6V6
V-5: 6V6
V-3: 12AU7
V-4: 12AX7
V-2: 6AU6 - but I can modify that to a 12AX7 easily enough
V-1,8,7,9: not using

Anything else you need?

[Paul1453]

I wasn't familiar with that specific model's layout.

It seems to be laid out similar to our guitar amps.
Many other organ amps aren't.

There are certain challenges in reusing the chassis,
but on this model they don't appear to be overwhelming.

The toughest part for you will likely be developing a layout,
that can re-use the parts board already in there.   

[frpax]

The toughest part for you will likely be developing a layout,
that can re-use the parts board already in there.   

That's EXACTLY what I need, a layout!

[Paul1453]

OK, but the layout depends on the parts placement.

With the 6V6 Plexi I made I have 6 pots on the front, and the NFB presence pot on the back.

Do you have the front 6 pot locations planned on this chassis?
They need to be kept away from noisy areas, like the PS and OT.

Then you want to use your board as efficiently as possible.
Keeping your leads short and away from problem areas.
Depending on the pots placements, this may require a significant departure from the traditional layout plan.
Or you could try to just copy the parts board layout and make your leads whatever length they need to be.

I really try hard to keep my leads as short as possible and away from problem areas.
But I have significant experience in Point to Point wiring, and now some experience in modifying a board's layout.
It takes lots of planning to get this right.

Practice following the schematic through the boards layout, you'll figure that out after a while.
Then if a layout change is necessary, you will have an idea about what needs to move and where it should go.
You will learn a great deal figuring this out on your own.   

Unless Sluckey already has a layout plan for this, I doubt anyone will want to develop a custom layout for you.  Sorry.
It is a lot of work to develop a trouble free layout plan.   

[frpax]

Thanks Paul.

I figured doing a layout was a lot of work.
Sluckey mentioned using Visio for his planning. It would be beyond my wildest dreams if Visio converted a schematic to a layout!

[Paul1453]

If no custom layout plan is available,

Using Doug's chassis and board is still a good option.   

I suspect you could get those and a few misc parts needed to build the 6V6 Plexi for around $100.

If you got the organ amp for free, and can make a Plexi out of it for anything less than $200, you are doing good.  IMO

Take a look at the BOM on Doug's plans.
If you were to buy all the parts from him for this amp,
it would cost around $450 not including shipping.   

[frpax]

If no custom layout plan is available,

Using Doug's chassis and board is still a good option.   

I suspect you could get those and a few misc parts needed to build the 6V6 Plexi for around $100.

If you got the organ amp for free, and can make a Plexi out of it for anything less than $200, you are doing good.  IMO

Take a look at the BOM on Doug's plans.
If you were to buy all the parts from him for this amp,
it would cost around $450 not including shipping.   

Where can I find Doug's plans?

[Paul1453]

http://el34world.com/schematics.htm#Plexi_6V6_build

 

[frpax]

OK, so help me out here for a sec, please.

I'm working very hard to visualize the schematic to the real thing.
So I follow the power cord into the the PT (T7) and then out to the rectifier tube/6V6 heaters/etc., which is on the lower portion of the schematic. Then the circuit has to connect to the part of the schematic that is at the top somehow.
Does the "+290" at the bottom connect to the "+290" at the top by the OT (in RED)?
And the "310" at the bottom is the "310" at the top (in GREEN)?
And I assume that everything in the ORANGE bubble should stay exactly intact?

[Paul1453]

The schematic shows you have a field core speaker as part of your PS.

This is not part of the normal 6V6 Plexi PS.
If you have the FC speaker and it works well,
you could probably modify the Plexi PS to keep it.

I modified my 6V6 Plexi PS and used +325VDC for my B+,
This PS is even less than that.
Doug's plan has over 400V for B+ I think.

If you want to get all the power you can out of the 2 6V6s,
then they normally jack up the voltage well above 400V.
I like to run my vintage tubes a little more conservatively.   

[frpax]

Yes, I do have the field coil speaker and I assume it works... I had to repair a few tears with some hot glue.

As for my vintage 6V6's, I'm not looking to get the most out of them. Just looking for good tone that isn't TOO hard on them.

At this point, I am thinking that I'll keep this schematic and just run with what I've got.

By looking at my schematic with the bubbles and lines on it, am I thinking right, that the ones indicated connect together?

[Paul1453]

Yes your Red and Green blocks are your voltage supplies.

That circuit looks like it should sound pretty good as a guitar amp.

It might be easiest to get that circuit up and then see if you really want to mess with it.   

[guitardude57]

I have used organ chassis for guitar amps, and found myself figuring what needed to be done first... to the power supply, in order for it to function how I need it to.   Then I remove the board, and clear the parts off of it.  You then can figure out values of the old parts individually, and use only the ones that test out in the specs you need.  Audio path passive circuits can use some of the old Carbon Comps...but the rest you are better off using metal film resistors, and NEW Electrolytic caps.

The board you have there is huge, and has enough space to build nearly anything.

You can choose from hundreds of layouts to build whatever style amp you want...it starts with part placement related to the tubes, input and control pots.  You have plenty of good places to ground things in there as well.

Just do some research on parts choices for your build, ideal locations... to keep unwanted interactions from occurring, (wiring and circuit related) and translate a layout to your board.

It really is not that difficult.  If you do not understand electronics enough...on this one, find a tech friend to help lay out your amp, and learn as you go.

[frpax]

Yes your Red and Green blocks are your voltage supplies.

That circuit looks like it should sound pretty good as a guitar amp.

It might be easiest to get that circuit up and then see if you really want to mess with it.   

That's my intention. Run with what I've got, and if I hate it, then I'll start really changing it.

[frpax]

I originally wanted to place my pots on the same side that the OT is, that is, the opposite side of the tube sockets.
But if they should not be near any transformers, do I need to place them on the same side as the tube sockets?
That would really clutter up that side of the chassis, so is it absolutely necessary?

[Paul1453]

Nice response guitardude57   

You are absolutely correct that it really is not that difficult.
It can be learned, and practice makes perfect.

Honestly though, it takes a lot of dedicated work and that takes a lot of time.
I don't mind that, it keeps me busy and learning.

I think others without previous electronic experience may find the whole process rather overwhelming without some SME guidance like you just gave.

SME = Army jargon for Subject Matter Expert 

[Paul1453]

I originally wanted to place my pots on the same side that the OT is, that is, the opposite side of the tube sockets.
But if they should not be near any transformers, do I need to place them on the same side as the tube sockets?
That would really clutter up that side of the chassis, so is it absolutely necessary?

These are the challenges of re-using the organ chassis.

I had spent much time just staring at my junk organ amps,
trying to figure out what I needed to do to make it a guitar amp.

HBP finally got me over my mental block of the organ amp parts being locked into their current positions.

You need to visualize the parts you have as a clean slate.
Find a proven layout for the guitar amp you want to build.
Then try to visualize how you can place the parts you have like they are on the amp you want to build.
Figure out if that is feasible using the same organ chassis.
It will likely require drilling new holes for parts and maybe covering the old holes.
Lots of work that you will need to figure out mostly on your own.

[sluckey]

What are the dimensions of your AO-29 chassis?

[frpax]

What are the dimensions of your AO-29 chassis?

21.5 x 5 inches

[sluckey]

What's the third dimension?

[frpax]

What's the third dimension?

Duh.. Depth is 2.5"

[Paul1453]

Those dimensions seem adequate to fit the Plexi circuit in to me.   

I think Sluckey and Doug have both built the 6V6 Plexi in a chassis smaller than that.

It's working out all those little challenges of part placement, and making the holes etc. for them to fit.

I'm interested in seeing your progress with whatever path you choose.   


I built my 6V6 Plexi in a Hammond Organ H100 Series Amplifier AO-70-1 chassis.
It was the build that finally got me over my parts placement visualization roadblock.
I've got less than $100 in junk parts into mine.
But realistically, well over $1000 in man hours to get it built.
It certainly won't win any build beauty contests.
But it sounds fantastic, and doesn't have any hum or noise issues.
Later, I'll try to post a picture of my ugly duckling Plexi for you to check it out.   

[sluckey]

I would suggest this layout (or very similar) for that AO-29 chassis. My turret board will not work in this chassis because my board is too wide and your tube layout calls for a board that's kinda a mirror image of my board. Same situation with Hoffman's board. So you gotta roll your own board. Everything should fit on the suggested board size.

I do not recommend using that 380-0-380vac PT from that AO-29. Your B+ will be way too high.

[Paul1453]

sluckey has visualized and documented an excellent example of a parts placement that will fit your organ chassis.   

He has located the parts so that you can keep your leads short and away from problem areas.
I expect that if you used his suggested parts placements, you would have a successful, problem free build.

Unfortunately, you still need to be able to translate the schematic to your circuit board layout.
This is where many of those untold man hours begin to accumulate.
It might be frustrating for you to do that at first.
But if you stuck to it and worked through the process you would learn a great deal.

If you feel that rolling your own circuit board is beyond your abilities at this time,
that pretty much forces you to go with Doug's chassis and proven circuit board.
That is, if you really want to make a 6V6 Plexi out of what you have.   

[frpax]

I would suggest this layout (or very similar) for that AO-29 chassis. My turret board will not work in this chassis because my board is too wide and your tube layout calls for a board that's kinda a mirror image of my board. Same situation with Hoffman's board. So you gotta roll your own board. Everything should fit on the suggested board size.

I do not recommend using that 380-0-380vac PT from that AO-29. Your B+ will be way too high.

Sluckey, you're da MAN!
This is what I have been envisioning, and you have the components in nearly the identical places that I've been thinking about.
As for a PT, what do you suggest I replace it with?

[frpax]

sluckey has visualized and documented an excellent example of a parts placement that will fit your organ chassis.   

He has located the parts so that you can keep your leads short and away from problem areas.
I expect that if you used his suggested parts placements, you would have a successful, problem free build.

Unfortunately, you still need to be able to translate the schematic to your circuit board layout.
This is where many of those untold man hours begin to accumulate.
It might be frustrating for you to do that at first.
But if you stuck to it and worked through the process you would learn a great deal.

If you feel that rolling your own circuit board is beyond your abilities at this time,
that pretty much forces you to go with Doug's chassis and proven circuit board.
That is, if you really want to make a 6V6 Plexi out of what you have.   

Ive been watching some YouTube videos about making a custom board. I'm sure that I can do it.

If I'm going to do this much modification, I can probably use the layout from several Plexi 6V6's that I've seen.

This is going to be fun!

[Paul1453]

Here is a pic of my junk parts Plexi.

Built exclusively with old parts I had on hand.

It might not look that great, but she definitely Rocks.

This was my 1st real chassis reconfiguration and circuit board customization.
I learned a lot from it, and have gotten better at this whole process with each successive build.   

[frpax]

Based on the basic layout that Sluckey did, I've decided to shitcan my Hammond AO-29 schematic and go with a more straightforward Plexi 6V6 plan.

Suggestions are very welcome!!

[sluckey]

Go with Doug's Plexi 6V6. He sells every part you need, including punched chassis. He makes it easy. You don't even have to put together a parts list or do any of the dirty work. Just put it together following his layout.

[frpax]

Go with Doug's Plexi 6V6. He sells every part you need, including punched chassis. He makes it easy. You don't even have to put together a parts list or do any of the dirty work. Just put it together following his layout.

OK!

So I went with Sluckeys basic layout for my chassis and board. Then I converted Doug's turret board to fit my boards size.

I went from this:


to this, that fits my chassis:


I think it will work!

[frpax]

I found a small error between the layout of Doug's turret board and his actual board.

Take a look at the yellow circled areas.

Layout:


And actual turret board:


Which one is correct? Or does it even matter?


Here is his complete layout versus his completed actual board.

Layout:


Actual board:


Help, please? I'm going to order the board from Doug and I need to know which one or if it makes no difference!

[frpax]

I've been busy today!!

I've designed the cabinet for this chassis.

This is a little rough, but it should look a lot like this:

[sluckey]

Help, please? I'm going to order the board from Doug and I need to know which one or if it makes no difference!
Modify message

They are both electrically the same and will both work just fine. I suspect the actual board you get will look like the one in the pdf document layout, not the one in the photo of the prototype amp Doug first built.

Send Doug a pm if you need more info.

[Paul1453]

It can be a lot of work to re-purpose an organ chassis.
But I'm getting better at it each time I do it.   

Here's my not quite finished adaptation of Doug's 6V6 Plexi.
The addition of 2 more 6V6's worked out very well.

She's a killer amp, that just needs some final tweaks and her paint job completed.   

[frpax]

Since I need a choke for the Plexi 6V6, would a Fender BF Deluxe Reverb choke made by Mercury Magnetics work?

[Paul1453]

As long as the choke is rated for the mA of current you will pull through it you can use it.
The Henries rating deals with it's filtering capabilities.

Since the choke usually comes after the main B+ which is drawing the majority of the current,
there is usually no need to use an expensive, over current capable choke.
If you already have a beefier choke than necessary you could use it, I did on my Quad Plexi, but why buy a new one like that?
Most little chokes will work fine for a simple PP 6V6 circuit.   

[frpax]

As long as the choke is rated for the mA of current you will pull through it you can use it.
The Henries rating deals with it's filtering capabilities.

Since the choke usually comes after the main B+ which is drawing the majority of the current,
there is usually no need to use an expensive, over current capable choke.
If you already have a beefier choke than necessary you could use it, I did on my Quad Plexi, but why buy a new one like that?
Most little chokes will work fine for a simple PP 6V6 circuit.   

I happen to have a brand new MM Fender BFDR choke on hand and it is rather small in size.
I also happen to have a brand new MM Vox AC-15 choke and it is MUCH larger. About the size of an average Output Transformer.

The Fender one will easily fit my chassis real estate. The Vox, not so much...

Also, I have a new MM Fender Tweed Deluxe OT. Would that work better for my Plexi 6V6 instead of my Hammond one?

[Paul1453]

I am very unfamiliar with all those new parts.

I buy cheap, junk tube gear off Ebay.

Figure out, to the best of my ability, what my junk parts are capable of, and try to put them to good use.   

My Quad 6V6 has used parts that I paid less than $150 for.

It is not easy to do it this way, but if you are cheap like me it can work.   

[sluckey]

I happen to have a brand new MM Fender BFDR choke on hand and it is rather small in size.
I also happen to have a brand new MM Vox AC-15 choke and it is MUCH larger.

Use the Fender choke. It's fine. The Vox choke is much larger because all current for the entire amp must flow through it.

[frpax]

Use the Fender choke. It's fine. The Vox choke is much larger because all current for the entire amp must flow through it.

Thank you! I was looking at the MM website, and these little chokes are $48!!

[frpax]

I've been busy this week!

If you recall, the amp design is going to look something like this (I modified it a teeny bit):




So, here's the almost done front panel, rescued from the original organ (need to cut out the portion where the chassis will be):




And since the chassis had lots of holes in it and I needed it to look pretty, so I cut out some pieces of sheet metal from other unused parts of the amp and JB Welded them into place and then sanded it real smooth. The marks you see on the front of the chassis is where I'll be drilling holes for pots and switches, etc.:

Chassis front (upside down):


Disregard the messy work bench and dig the 1983 boom box which still works, by the way,  but only as a radio. Blasts out Classic Rock only!

Back:



Altogether, I'm very happy with how the project is coming along. I'm re-purposing many of the original organ stuff and also re-purposing a lot of other stuff I have collecting dust in my garage.

I'm selling off a bunch of power and output transformers (Mercury Magnetics and a couple Allen transformers on eBay in order to fund what I don't have to complete this. My user name is 6stringer if anyone is interested. I don't have them all listed yet, but will by tomorrow.

[Paul1453]

Wow!  You are doing a really fine job!

Much better than me.   

Looks like you have much better tools than I do.

Using nice new clean parts has a certain appeal to it.

But cleaning up some nasty junk that would have most likely ended up in a landfill and reusing the parts, is better IMO. 

Then making a kick ass guitar amp from it is something to be quite proud of.

Doing that at 1/4 or less of the new parts costs, helps to keep the wife off my case.   

[frpax]

Wow!  You are doing a really fine job!

Much better than me.   

Looks like you have much better tools than I do.

Using nice new clean parts has a certain appeal to it.

But cleaning up some nasty junk that would have most likely ended up in a landfill and reusing the parts, is better IMO. 

Then making a kick ass guitar amp from it is something to be quite proud of.

Doing that at 1/4 or less of the new parts costs, helps to keep the wife off my case.   

Thanks, Paul!

I don't have any really special tools, per se. I used a Dremel to cut the fill in pieces on the chassis. Then an orbital sander to sand it smooth. I used a circular saw on the front panel and will use a jigsaw to cut the part out for access to the controls. I REALLY wish I had a table saw for that... would have saved me a ton of time. I do have a router, that I'll be using to round off all the corners of the cabinet.

Just a lot more time involved by having minimal power tools. And I'm really taking my time. Measuring twice and cutting once, that sort of thing. It's more a job of paying attention to details.

[frpax]

While waiting for some money to come in so I can work on my amp, I still have been busy working on the cabinet.

Here are a few quick pics:







All the wood except the bottom are from the original organ!

[frpax]

I made the back slats out of that thing on the organ that folds up to hold the sheet music:

[frpax]

A few more, this time with the empty chassis installed and the tweed corner on the front:








Still have to round the squared corners with a router.
Also, I'm going to buy some either black or gold piping to go around the front speaker panel and that tweeded corner.

I think it's looking fairly decent. It would be nicer (meaning more square) if I had a table saw. But you do what you can do, right?

[Paul1453]

It's looking outstanding to me!   

Don't be too hard on yourself, and sing:

"I know, it's only Rock-n-Roll, but I Like it"!

"I Like it, Like it, Yes I do"!   

[frpax]

It's looking outstanding to me!   

Don't be too hard on yourself, and sing:

"I know, it's only Rock-n-Roll, but I Like it"!

"I Like it, Like it, Yes I do"!   

Thank you!

I had to change a few things from both my original AND revised designs. Some things look great on paper (literally!), but don't work out so well unless you have the proper tools. Oh well, I'm still pretty pleased with how it is looking!