Hammond AO-29 amp convert to Plexi 6V6?

[sluckey]

"feedback" has me confused. Do I run a wire from the board to the speaker jack?

yes

does everything look copacetic?

rectifier tube looks good. I don't understand why you crossed out the center tap ground connection on the PT red winding? That CT must be connected to ground. Concerning your power inlet wiring... White wire is used with Neutral, black wire is used with line. If you are just using a power cord, then connect the black to the fuse and connect the white directly to the PT. And green to a dedicated chassis bolt with no other ground connections.

[Paul1453]

Looking good.

The only thing left for you to maybe consider since you are using a tube rectifier, is the "Immortal Amp" mod?

Basically, it just adds 2 diodes to your rectifier socket to help protect your PT.

It is very cheap insurance, IMHO. 

[frpax]

"feedback" has me confused. Do I run a wire from the board to the speaker jack?

yes

does everything look copacetic?

rectifier tube looks good. I don't understand why you crossed out the center tap ground connection on the PT red winding? That CT must be connected to ground. Concerning your power inlet wiring... White wire is used with Neutral, black wire is used with line. If you are just using a power cord, then connect the black to the fuse and connect the white directly to the PT. And green to a dedicated chassis bolt with no other ground connections.

The PT has a green cloth insulated wire that went to ground. I was told to take that wire & the green cord wire and put terminal lugs on them and ground them to the same spot, like one of the corner PT bolts.
That red wire that I crossed off, originally went to the field coil connector that then connected to the FC speaker. Since I am now going to use a permanent magnet speaker, I didn't figure that wire to be of any use, especially since I have that green grounding wire from the PT.
From power cord, black to fuse, then on/off switch, then to PT. White direct to PT. And green to the aforementioned ground.

[frpax]

Looking good.

The only thing left for you to maybe consider since you are using a tube rectifier, is the "Immortal Amp" mod?

Basically, it just adds 2 diodes to your rectifier socket to help protect your PT.

It is very cheap insurance, IMHO. 

Paul, can you give me more specifics? What type diodes and where do I connect them?

[Paul1453]

Time to learn how to use the search feature here.   

You will find the info on other threads here, no need for a rehash.

It is a very simple mod, and after you read about it, if you still have questions someone will square you away.   

[frpax]

Time to learn how to use the search feature here.   

You will find the info on other threads here, no need for a rehash.

It is a very simple mod, and after you read about it, if you still have questions someone will square you away.   

Gothca.

[sluckey]

That red wire that I crossed off, originally went to the field coil connector that then connected to the FC speaker. Since I am now going to use a permanent magnet speaker, I didn't figure that wire to be of any use, especially since I have that green grounding wire from the PT.

The green wire from the PT has nothing to do with this center tap wire. It's not optional. ***YOU MUST CONNECT THAT CENTER TAP TO SOMETHING!*** You will have NO B+ voltages if you don't connect that wire to something. Now you can connect that CT directly to ground and your B+ will be about 100V higher than you will want. Or, you can connect a 700Ω 30 watt resistor between that wire and chassis to simulate the missing field coil.

[PRR]

> I run a wire from the board to the speaker jack?

Yes. We want the amp to "know" what is happening at the speaker.

Impedance tap is not so fussy. It looks like the plan taps off the 8 ohm winding, so if you have 8 use that. But 4 or 16 is not so different. And in the final stage, tweaking the amp to a speaker and a player, you should try different values for the "feedback" resistor. Looks like 47K? Try (in your near-final form) 22K and 100K against 47K. Higher values give more gain and more flavor, lower values less gain and more polite.

[frpax]

That red wire that I crossed off, originally went to the field coil connector that then connected to the FC speaker. Since I am now going to use a permanent magnet speaker, I didn't figure that wire to be of any use, especially since I have that green grounding wire from the PT.

The green wire from the PT has nothing to do with this center tap wire. It's not optional. ***YOU MUST CONNECT THAT CENTER TAP TO SOMETHING!*** You will have NO B+ voltages if you don't connect that wire to something. Now you can connect that CT directly to ground and your B+ will be about 100V higher than you will want. Or, you can connect a 700Ω 30 watt resistor between that wire and chassis to simulate the missing field coil.

OK, so if I put a 700 ohm / 30 watt resistor between that red center tap and the chassis, and the green still goes to ground? Or do I not use it at all?

[sluckey]

and the green still goes to ground?

yes

[frpax]

Or, you can connect a 700Ω 30 watt resistor between that wire and chassis to simulate the missing field coil.

I've been doing some internet searching for such a beast and am coming up empty. Where can I get one?

[sluckey]

http://www.mouser.com/ProductDetail/Vishay-Dale/RH050700R0FE02/?qs=sGAEpiMZZMtTURnxoZnJAHlhF1kLzuAqgg5mGcFi6Kw%3d

[PRR]

> searching for such a beast

Three 2.2K 10W in parallel.
Three 750r 10W in series.

[frpax]

> searching for such a beast

Three 2.2K 10W in parallel.
Three 750r 10W in series.

Good to know! Thank you

[frpax]

Mail came today! Nice Fender Brown Face knobs!



It's starting to take shape! In a couple of weeks, it will be DONE! I'm excited, to say the least!

[frpax]

Lesson learned.

I should have used turrets instead of eyelets.

[frpax]

Two questions:

1. The schematic shows a couple of things going to "E" on the board. But the layouts show nothing going to "E". How do I reconcile this?

Schematic:



2. When attaching the PT to the heaters, the photos of Doug's build (which he said are of the prototype and in some cases should not be used as a guide) show something like this:



This is from PT to V5 pins 2 & 7 to V4 pins 2 & 7 and then from V4 pin 2 to V3, V2 and V1 pin 9 (in series?) and V4 pin 7 to V3 pin 5, V3 pin 4 to V2 pin 5 then V2 pin 4 to V1 pin 5 with V1 pin 4 open.

Is this the correct way to do this? Please advise.

Thanks, as always!

[PRR]

> things going to "E" on the board. But the layouts show nothing going to "E".

[frpax]

> things going to "E" on the board. But the layouts show nothing going to "E".

Thank you.
After seeing that pic and looking again at the schematic, I see that the layout is correct.

You are a great help, PRR!

[Willabe]

Lesson learned.

I should have used turrets instead of eyelets.

Why?   

[frpax]

Lesson learned.

I should have used turrets instead of eyelets.

Why?   

In some cases, 3 wires will not fit into an eyelet.

[Willabe]

Are your using stranded wire and large 16g, 18g?

I've done a few boards where I used both eyelets and turrets. I used the turrets where I had a lot of wires going to 1 termination point. It worked well for me.

I've also have used turrets to lift parts above other parts when crossing over at 90 degrees. 

[frpax]

Are your using stranded wire and large 16g, 18g?

I've done a few boards where I used both eyelets and turrets. I used the turrets where I had a lot of wires going to 1 termination point. It worked well for me.

I've also have used turrets to lift parts above other parts when crossing over at 90 degrees.

Solid wire, 20g. 3 just don't like to fit.

[kleyplays]

Under V3 in purple on the board there is a connection for that Feedback resistor. 

[frpax]

Couple MORE questions!

1. In the layout, what is the relation between the Bias Tap & Bias Range?




2. Since the pots are all attached to the chassis (which, in my my mind grounds them), do I really need to run a grounding wire across the back of them all? Or should I just ground the appropriate lugs to the backs of the pots?

[sluckey]

1. Bias tap denotes the AC voltage source for the bias circuit, in your case, the top side of the HT winding. Bias tap could be a dedicated 'tap' on the HT winding, a totally separate secondary winding, or even another PT specifically for bias. Bias range refers to a resistor that you can change the value if your bias adjustment range needs to be raised or lowered to suit your particular tubes. You may have to change the value of that resistor since you are using an oddball PT.

2. You don't have to connect that ground buss to the back of the pots. It's a personal choice. Hoffman does, I don't. But in either case, the ground buss will provide a more reliable ground connection than just soldering the pot lug to the back of the pot. I know that Fender did this, but he also had a brass plate sitting under the pots. This brass plate served as a ground buss but it was prone to problems due to dissimilar metals. I advise you don't solder the lug to the back of a pot.

[frpax]

Thanks sluckey. Comments in color in the quote section:

1. Bias tap denotes the AC voltage source for the bias circuit, in your case, the top side of the HT winding. Bias tap could be a dedicated 'tap' on the HT winding, a totally separate secondary winding, or even another PT specifically for bias. Bias range refers to a resistor that you can change the value if your bias adjustment range needs to be raised or lowered to suit your particular tubes. You may have to change the value of that resistor since you are using an oddball PT. So, there is no wire that connects those two. The labels on the layout are for reference. Correct?

2. You don't have to connect that ground buss to the back of the pots. It's a personal choice. Hoffman does, I don't. But in either case, the ground buss will provide a more reliable ground connection than just soldering the pot lug to the back of the pot. I know that Fender did this, but he also had a brass plate sitting under the pots. This brass plate served as a ground buss but it was prone to problems due to dissimilar metals. I advise you don't solder the lug to the back of a pot. I understand. I'll stick with the layout. Since the Presence pot is now on the opposite side of the chassis, would it suffice to just have that one with the lug grounded to the back of the pot?

That Center Tap wire from the PT that I was originally not going to use... I'm going to get that behemoth resistor from Mouser, but (like any other resistor I've seen, it has two terminal points. Does the CT go to one, and the other to ground? Or what?

[sluckey]

So, there is no wire that connects those two. The labels on the layout are for reference. Correct?

That's correct.

Since the Presence pot is now on the opposite side of the chassis, would it suffice to just have that one with the lug grounded to the back of the pot?

No. Run a wire to your power ground point, probably a PT bolt. Soldering a pot lug to the back of the pot is not a reliable ground connection IMO.

Does the CT go to one, and the other to ground?

Correct.

[frpax]

So, there is no wire that connects those two. The labels on the layout are for reference. Correct?

That's correct.

Since the Presence pot is now on the opposite side of the chassis, would it suffice to just have that one with the lug grounded to the back of the pot?

No. Run a wire to your power ground point, probably a PT bolt. Soldering a pot lug to the back of the pot is not a reliable ground connection IMO.

Does the CT go to one, and the other to ground?

Correct.

Man, I've got a shitload of things to ground!!

[frpax]

I ordered the last parts I'll need (hope upon hope) for this thing: the resistors and caps that go directly onto the board.

Since this is my first try at this, I'm actually quite frightened to plug the thing in! I'd really hate to have it blow up or catch my house on fire. My wife would be even more angry. That'd probably push her over the edge to divorce-ville. That'd sure suck.

[EKDENTON]

I made a simple light bulb current limiter to use when starting up my last amp. They are very simple to build and you will be able to tell if you have a direct short. its just a short extension cord with a light bulb in series with either the black or white wire in your extension cord. Their may be a plan here in the amp library section here on this site, if not you can just google it and there are tons of examples online.


Here I found a drawing:

[frpax]

I made a simple light bulb current limiter to use when starting up my last amp. They are very simple to build and you will be able to tell if you have a direct short. its just a short extension cord with a light bulb in series with either the black or white wire in your extension cord. Their may be a plan here in the amp library section here on this site, if not you can just google it and there are tons of examples online.


Here I found a drawing:

Very cool! I had recently seen one of these, but wasn't quite sure how it worked or if it even applied to me.
Thanks!

[frpax]

A little more progress today:









Good old DYMO label maker. Comes in handy every once in a while! 

Just waiting for the last few parts to come in and by mid-week, I should be firing it up (and likely trying to figure out what I did wrong OR what's not working!). Yes, I have very little faith in this, my first attempt!

But, I will say that my soldering skills have gotten MUCH better from when I first started fooling around with pickup swaps, etc. Back then, I was the undisputed KING of the cold solder joint! 

[frpax]

When attaching the PT to the heaters, the photos of Doug's build (which he said are of the prototype and in some cases should not be used as a guide) show something like this:



This is from PT to V5 pins 2 & 7 to V4 pins 2 & 7 and then from V4 pin 2 to V3, V2 and V1 pin 9 (in series?) and V4 pin 7 to V3 pin 5, V3 pin 4 to V2 pin 5 then V2 pin 4 to V1 pin 5 with V1 pin 4 open.

Is this the correct way to do this? Please advise.

[sluckey]

That's fine. Don't forget the jumpers between pin 4 and 5 on ALL little tubes.

[frpax]

That's fine. Don't forget the jumpers between pin 4 and 5 on ALL little tubes.

Got it. Thanks again!

[frpax]

Started on the eyelet board.

Any concerns?

[Paul1453]

It appears to me that your big black E-cap is installed backward.   

And the little blue one too.   

Another suggestion for your heater wires.
Since these are usually VAC we tend to twist them together to help cancel hum.
You have used brown wires.
I usually would use something like a brown wire and a brown with white stripe wire.
To twist them up easily you can put these 2 wires in your drill like a drill bit and tighten it down.
Then just slowly squeeze the trigger and nicely twist up a decently long string of these wires.
I then try to cut them just a little longer than needed to reach between the sockets.
Untwist just enough on each end to make a clean connection at the socket.
It's debatable if it is necessary or not, but putting the white stripe wire on 4-5 and brown on all 9s seems to at least look organized.   

[frpax]

It appears to me that your big black E-cap is installed backward.   

And the little blue one too.   

I'm pretty sure the black one is, but I will check them both.

How about the buss wire that runs from eyelet to eyelet? Should I have put that on the other side of the board? Any potential concerns there?

[frpax]

In this, Doug's layout is shown by the black line.
I have it wired like the green.
Is there any difference?




Also, on the pic above of my board (with the upside down filter caps, that I will fix), am I OK with the buss wire one the top side of my board? Are there any problems or potential problems with it this way?

[sluckey]

Is there any difference?

Yes. Your green wire is longer than Doug's black wire.   

am I OK with the buss wire one the top side of my board?

yes

Are there any problems or potential problems with it this way?

no

[frpax]

OK!

I am 99.9% sure that I've got everything done correctly (hope upon hope!)

Here's a pic. Could you guys look at it and tell me if it all looks alright to you?



I redid the heater wiring like Paul suggested and got my caps now oriented the correct way. I continuity tested everything that I could think of and got positive results from that.

All I need to do now is put the tubes in and plug it in, I think!

[Willabe]

I made a simple light bulb current limiter to use when starting up my last amp. They are very simple to build and you will be able to tell if you have a direct short. its just a short extension cord with a light bulb in series with either the black or white wire in your extension cord. Their may be a plan here in the amp library section here on this site, if not you can just google it and there are tons of examples online.
Here I found a drawing:

Don't forget the light bulb limiter for 1st start up. Here's another link from Sluckey's web site that has some instructions on how to use it;

http://sluckeyamps.com/misc/Amp_Scrapbook.pdf

[frpax]

OK!

It makes good sounds!
Nothing exploded!
I didn't get electrocuted nor burn my house down!

It's not entirely done yet, but here's what I've got so far:

[sluckey]

Don't it feel good!

[frpax]

Don't it feel good!

An incredible sense of accomplishment!

Thanks to EVERYONE who helped me!

After this on is completely done, I wonder what I'll build next? 

[Paul1453]

What you have built also has a very cool old school appeal to it, IMO.

Not a sterile metal and plastic look, but a hand crafted woodworking style!  ;^)

[frpax]

What you have built also has a very cool old school appeal to it, IMO.

Not a sterile metal and plastic look, but a hand crafted woodworking style!  ;^)

Well, the organ was made like a piece of furniture (for that time) and that was the look I was after.

[EKDENTON]

Awesome! Good Job!!

[frpax]

Sooooo, never being quite satisfied with things, I started messing around with it today.
I was liking the tone from the 6V6's, but not the volume. With the volumes dimed, it was above bedroom level, but well below band practice level.
So I put these in  :




 

I biased it a tad cooler than the 6V6's but still enough to give it some oomph.

HOLY COW! This little amp absolutely came ALIVE! The tone is even better than the 6V6 variant,  and it now has a nice set of balls!

I am over the MOON with this thing now!!



Yes, the 6L6's are a tad close to one another, but then, the choke is a tad close to the PT. Not ideal, but it is what it is.