Pro Junior Conversion

[flyby71]

Hi everyone! I have decided to attempt my first amp conversion and am staring with the Hoffman Pro Junior conversion.

This will be a slow learning process for me. I have the chassis stripped down and am getting ready to install off board components. I think I have a basic understand of where most of the wires run at this point. I am confused on a couple of spots however.

Can anyone post a few photos of a Pro Junior conversion that you have done…..more specifically of the tube socket wiring and how the led light was wired in? I may be able to answer my questions from photos.

Thanks!

[uki]

Welcome to the forum!

Start here:  https://el34world.com/schematics.htm   roll all the way to the bottom there is plenty useful info there

I think its much easier to search on google images for pictures, that is usually what i do, there tons of pictures for reference.

[flyby71]

Welcome to the forum!

Start here:  https://el34world.com/schematics.htm   roll all the way to the bottom there is plenty useful info there

I think its much easier to search on google images for pictures, that is usually what i do, there tons of pictures for reference.

Thanks. I have looked at the schematics and still have a couple of questions.

Google isn’t helping with what I need for a picture either. That’s what I was hoping someone here who has done one of these exact conversations could upload a picture or two.

 I can type out my questions and hopefully they will make sense.

[bmccowan]

Did you look at the project that Doug completed - about 2/3 of the way down the page the uki posted. He has pics and descriptions - not just a schematic.

[flyby71]

Did you look at the project that Doug completed - about 2/3 of the way down the page the uki posted. He has pics and descriptions - not just a schematic.

I did find those pics from the one he did. The problem is that he made a couple of changes between that and the final product, which unfortunately is where my issue is!

Let me gather my thoughts about this and I’ll post my questions in a bit.

[flyby71]

Here goes….If I am not explaining my questions clear enough, please let me know and I’ll do my best to clarify.

Here are the first few questions:

Where do the two green wires from the power transformer run to? Do they run to the two lugs where the 47’s are on the right side of the board, then two new green wires from the lugs to the tube sockets? I’ll try to display this in a photo.

How/where do I tie the two wires from the led light into the green wires and 180?

[flyby71]

Doug used a three lug terminal strip on the original build (pic attached). That is not used on the final design and some of the board components have moved/changed.

[EL34]

It says right in the instructions this

Note that Hoffman boards are not assembled by looking at my builds.
I do test builds first and change the designs based on those builds.
You assemble Hoffman boards using the documents listed under each board on the library page here

So don't follow my test build photos

You use the documents listed here
https://el34world.com/schematics.htm#Hoffman_Pro_Junior_Conversion

[flyby71]

It says right in the instructions this

Note that Hoffman boards are not assembled by looking at my builds.
I do test builds first and change the designs based on those builds.
You assemble Hoffman boards using the documents listed under each board on the library page here

So don't follow my test build photos

You use the documents listed here
https://el34world.com/schematics.htm#Hoffman_Pro_Junior_Conversion

Yes sir, I understand. I apologize if I wasn’t clear in that.

 I am going by the documents that you linked. I am just stuck and unclear of how/where to attach/hook up the green filament wires and the led light wires.

[flyby71]

It says right in the instructions this

Note that Hoffman boards are not assembled by looking at my builds.
I do test builds first and change the designs based on those builds.
You assemble Hoffman boards using the documents listed under each board on the library page here

So don't follow my test build photos

You use the documents listed here
https://el34world.com/schematics.htm#Hoffman_Pro_Junior_Conversion

In reply #5 I made some drawings on a couple of photos to try to illustrate where I am stuck and my best guess as to what it appears needs to be done. Do you have any guidance that you could offer on those?

[EL34]

The Layout diagram and schematic show you exactly where the green wires go
Are you looking at this document?
https://el34world.com/Hoffman/files/Hoffman_Pro_Jr.pdf
Where does it show them going?

[flyby71]

The Layout diagram and schematic show you exactly where the green wires go
Are you looking at this document?
https://el34world.com/Hoffman/files/Hoffman_Pro_Jr.pdf
Where does it show them going?

Yes, I am looking at that document. I am new to this and am trying to learn. I truly do not know for certain where they go. It looks like it could go two different ways.

There are only two of the 47 resistors and they are on the turret board. That makes me think that the green wires run to the lugs where the two 47 resistors are, and go to the heater lugs from there. If the green wires do not go to the 47 resistors on the turret board, then it looks like I am missing two 47 resistors.

 I’m not trying to be difficult. I assumed this was a place to come and ask these questions. I am just trying to get help. I am trying to learn where they go and how the LED wires and resistor fit into this. Again, I’m new at it and am doing my best to learn. A little help and advice would be greatly appreciated.

[Willabe]

There are only two of the 47 resistors and they are on the turret board. That makes me think that the green wires run to the lugs where the two 47 resistors are, and go to the heater lugs from there.

Yes, you have that correct. The green heater wires go to 2 x 47 ohm resistors on the very end of the eyelet/turret board. 

[flyby71]

There are only two of the 47 resistors and they are on the turret board. That makes me think that the green wires run to the lugs where the two 47 resistors are, and go to the heater lugs from there.

Yes, you have that correct. The green heater wires go to 2 x 47 ohm resistors on the very end of the eyelet/turret board.

Thank you so much! You have no idea how much that helps! I have mocked up how I think it goes (I know the resistors are wrong values, just using them as an example).

Does this look correct?

[Willabe]

Yes, that looks correct.

Follow Hoffman's schematic and his drawing that's right before his schamtic.

And the heater wires, make them a nice evenly twisted pair. And on the preamp tubes sockets, run them over the center of the tube sockets, not around the socket, like in this from Merlin. Or over the top.

Scroll down to the bottom for picture of wired tube socket.

https://www.valvewizard.co.uk/heater.html

[flyby71]

Yes, that looks correct.

Follow Hoffman's schematic and his drawing that's right before his schamtic.

And the heater wires, make them a nice evenly twisted pair. And on the preamp tubes sockets, run them over the center of the tube sockets, not around the socket, like in this from Merlin. Or over the top.

Scroll down to the bottom for picture of wired tube socket.

https://www.valvewizard.co.uk/heater.html

Good deal. Thank you for taking a look at it. I feel confident in moving forward now.

Good info to know about how to wire the sockets. I would have gone from the side instead of how the article you linked instructs.

Thanks again!

[EL34]

When you looked at the layout and the schematic, what did these two areas show you?
Did you see this info?

[kagliostro]

I think he is asking were to route the twisted wires from the 47R resistor till the connections pins on tubes (I suppose near the inside chassis corner)

Franco

[Willabe]

I think he is asking were to route the twisted wires from the 47R resistor till the connections pins on tubes (I suppose near the inside chassis corner)

Yes, maybe? 

[kagliostro]

See here

Franco


p.s.: This kind of info can easily be recovered on the web
BTW the first example is something that was published by Mr Merlin on his books and you can see it having a Google search

[EL34]

I am a little bit concerned that this is fairly easy stuff and hopefully he gets through the build

My boards are not snap together models
You need some previous skills and basic knowledge before you tackle one of my boards

[flyby71]

When you looked at the layout and the schematic, what did these two areas show you?
Did you see this info?

I am new at this, and as I said in my original post, this is my first amp conversion. I am learning as I go. I did not try to hide that.

I was able to get this amp for a cheap price and thought it would be a good one to start with. That’s the reason for these basic questions……I’m learning as I go.

When I look at those two that you just posted, which I really have spent sooo much time looking and trying to make sure I am understanding, they look opposite to me.

The top drawing appears that the filament wires from the transformer connect with the wires from the LED, then to the resistors on the turret board, and then go to the tube sockets.

The bottom drawing appears to me that the filament wires come from the transformer to the tube sockets, and then to the resistors and LED wires. they look the opposite directions to me.

Again, learning as I go and I was hoping for some of the fine folks here to walk me through these questions that I had. Willabe was a huge help with his answers and it started to give me a better understanding.

[flyby71]

I think he is asking were to route the twisted wires from the 47R resistor till the connections pins on tubes (I suppose near the inside chassis corner)

Franco

I was asking about where to physically hook up the filament wires from the transformer and wires from the led light. I was unclear on that part.

I understand where to run the twisted wires to the tube pins.

[EL34]

There is no difference between those two.
It's two parallel wires with loads attached between them

That's why I am questioning.
This is something that should be understood before attempting a huge project like this.

[flyby71]

See here

Franco


p.s.: This kind of info can easily be recovered on the web
BTW the first example is something that was published by Mr Merlin on his books and you can see it having a Google search

I am clear on how this part goes. The photos helped for sure, but this was not my point of confusion.

I was trying to figure out how and where the order of connecting wires was. I mocked up the wires in these photos to verify that I was correct.

I was just trying to verify that i understood where to make the connects correctly.

[flyby71]

I am a little bit concerned that this is fairly easy stuff and hopefully he gets through the build

My boards are not snap together models
You need some previous skills and basic knowledge before you tackle one of my boards

I said from the beginning that this was my first amp conversion. I am new to this process. I am learning. Doing the best that I can and the only way I know to learn is to read and ask questions.

The exact reason I joined this form was to work through this build and learn how to do this correctly. I assumed that this forum was a good place to come to get help working through this.

[flyby71]

There is no difference between those two.
It's two parallel wires with loads attached between them

That's why I am questioning.
This is something that should be understood before attempting a huge project like this.

I don’t think I was asking my questions in a clear enough manner. I was looking to confirm the order and location of how they connected. That’s why then took the photos of the connections mocked up and was trying to visually confirm that I was understanding.



I didn’t understand everything about this process before taking this on. I wanted to learn as I went. I have been very upfront about that. It was my bad for assuming that this was the place to come for help learning. If me asking these questions here and looking for help and advice is not what this place is for, then please tell me and I will move on. I’m just a guy trying my best to learn.

[bmccowan]

The exact reason I joined this form was to work through this build and learn how to do this correctly. I assumed that this forum was a good place to come to get help working through this.

This was exactly why I joined the Forum 10 years ago. I'm still learning - everyone is still learning at least some things. I sense that you are taking constructive criticism as personal insults. I see that a lot here, and urge you not to do so. Doug and the moderators have a responsibility to help people do things safely. When they sense a lack of understanding, they speak up. Good for them I say. It's true that you can build or repair an amp without an understanding of tube circuits. But, there are times when its best to stop and go back to the study hall. In the short term its frustrating in this rushed world, but in the end, you are better off.

I didn’t understand everything about this process before taking this on. I wanted to learn as I went. I have been very upfront about that. It was my bad for assuming that this was the place to come for help learning. If me asking these questions here and looking for help and advice is not what this place is for, then please tell me and I will move on. I’m just a guy trying my best to learn.

No it was not "your bad." But if someone suggests that the best course of action is to go back and read/study/think, it is done for good reason and with good intent.
Best of luck finishing your project.

[uki]

Nobody did mention this but since you are new to it, is important to know about the voltages inside tube amps.

The power transformer put out HIGH VOLTAGE and can be LETHAL.

So you have to be extra careful!

It is good idea to read this --> Tube Amplifier Safety

Learn how to read an schematic, it is fundamental to understand, how the amp works and how to connect wires, components, transformers and all else.
It is always better to follow the schematic even when we have the layout.

Do you have a multi meter? You'll need one.

[flyby71]

The exact reason I joined this form was to work through this build and learn how to do this correctly. I assumed that this forum was a good place to come to get help working through this.

This was exactly why I joined the Forum 10 years ago. I'm still learning - everyone is still learning at least some things. I sense that you are taking constructive criticism as personal insults. I see that a lot here, and urge you not to do so. Doug and the moderators have a responsibility to help people do things safely. When they sense a lack of understanding, they speak up. Good for them I say. It's true that you can build or repair an amp without an understanding of tube circuits. But, there are times when its best to stop and go back to the study hall. In the short term its frustrating in this rushed world, but in the end, you are better off.

I didn’t understand everything about this process before taking this on. I wanted to learn as I went. I have been very upfront about that. It was my bad for assuming that this was the place to come for help learning. If me asking these questions here and looking for help and advice is not what this place is for, then please tell me and I will move on. I’m just a guy trying my best to learn.

No it was not "your bad." But if someone suggests that the best course of action is to go back and read/study/think, it is done for good reason and with good intent.
Best of luck finishing your project.

I appreciate the advice. I have no problem with the constructive criticism. I can learn well from it. The comments from Doug were really starting to come across as condescending questionings and not trying to be helpful. That gets frustrating to me. But this is the reading a comment instead of verbal communication, and things don’t always come across as they are meant and the message isn’t always received as intended.

I want to learn these concepts and not just get through this one project. You are totally correct. I am taking a step back and will do some studying to learn reading schematics, how an amp works, concepts, etc. I am very interested in this process! Thanks for the tips, they are being put into practice!

[flyby71]

Nobody did mention this but since you are new to it, is important to know about the voltages inside tube amps.

The power transformer put out HIGH VOLTAGE and can be LETHAL.

So you have to be extra careful!

It is good idea to read this --> Tube Amplifier Safety

Learn how to read an schematic, it is fundamental to understand, how the amp works and how to connect wires, components, transformers and all else.
It is always better to follow the schematic even when we have the layout.

Do you have a multi meter? You'll need one.

The high voltage thing is actually the first thing I learned about and did learn  how to take steps to ensure safety. I had no clue about that until I started watching some amp repair videos. I have a very healthy respect for electricity!


Thanks for the link, I will spend the time reading it.

I 100% agree. I should have started by learning to read schematics before taking this project on, but I am taking a pause now to learn that!


I do have a multimeter, and am working at understanding its many uses.

[kagliostro]

Now I understand your question and which is the situation, but, I still don't understand if at this time you clarified in your mind what you have to do with those connections

Please say if in your mind is clear the answer to the question or if you prefer I (we) try to explain furtherly what is to be done

Franco

p.s.: There are not difficult things and easy things, there are only things we know or we don't know, but we can learn it if we want


We posted the same time

[flyby71]

Now I understand your question and which is the situation, but, I still don't understand if at this time you clarified in your mind what you have to do with those connections

Please say if in your mind is clear the answer to the question or if you prefer I (we) try to explain furtherly what is to be done

Franco

p.s.: There are not difficult things and easy things, there are only things we know or we don't know, but we can learn it if we want


We posted the same time

I really like that quote. It helps to keep things in perspective. An unknown is an unknown, just that simple. Good stuff!


Here is how I have this in my mind. If it’s not clear, I will try my best to clear it up!

Both green filament wires go from the PT and attach to the rightmost lugs on the turret boards (which are attached to the 47 resistors).

The white wire from the led attaches to one of the rightmost lugs with one of the filament wires.

The red wire from the led goes to a 180 resistor which is attached to the other rightmost lug that the other filament wire is attached to.

New green filament wires leave those lugs and go to the tube sockets V4 through V1.

A ground wire is run from the left lug that the 47 capacitor is attached to and grounded to the chassis.

I tried to draw this out. Please let me know if it’s not clear and I’ll redraw it.

[AlNewman]

That diagram looks like you figured out how the heater wiring should work.

If you're just starting out, especially with a new build, IMO the first thing you should do is build a light bulb limiter.  Not only for safety, but for confirmation as you build your amp.  Every time you flick the switch, plug it in through your LBL first, and you'll know immediately if there's a short in your wiring as you progress.  It can save a lot of troubleshooting and headaches down the road.

[flyby71]

That diagram looks like you figured out how the heater wiring should work.

If you're just starting out, especially with a new build, IMO the first thing you should do is build a light bulb limiter.  Not only for safety, but for confirmation as you build your amp.  Every time you flick the switch, plug it in through your LBL first, and you'll know immediately if there's a short in your wiring as you progress.  It can save a lot of troubleshooting and headaches down the road.

Interesting. I’ve never heard of one of those. I will google it now.

[bmccowan]

Doug's drawing is correct. Flyby's not so much. Same with the description. The two components labelled 47 are resistors, not capacitors.
And the two ends are grounded together, not just one of them.
The LBL is a great tool, if you have not heard of it I suggest that you have not done enough reading. That tool is everywhere here on the Forum.
And when building amps it's important to know what the components do. What do those two resistors connecting the heater wires to ground do? What does the resistor going to the LED pilot lamp do? For two examples.
One can approach amp builds as paint by numbers, I guess. But knowing the basics of what the circuits do is far more satisfying and will keep one on the right path.
Trying to help, so please do not take offence.

[flyby71]

That diagram looks like you figured out how the heater wiring should work.

If you're just starting out, especially with a new build, IMO the first thing you should do is build a light bulb limiter.  Not only for safety, but for confirmation as you build your amp.  Every time you flick the switch, plug it in through your LBL first, and you'll know immediately if there's a short in your wiring as you progress.  It can save a lot of troubleshooting and headaches down the road.

So I found some information and a few diagrams for building one. Thanks for the suggestion! I will be making one this weekend. I still have some reading to do to make sure I understand exactly how to use it and to make sure I get the right wattage bulb.

[flyby71]

Doug's drawing is correct. Flyby's not so much. Same with the description. The two components labelled 47 are resistors, not capacitors.
And the two ends are grounded together, not just one of them.
The LBL is a great tool, if you have not heard of it I suggest that you have not done enough reading. That tool is everywhere here on the Forum.
And when building amps it's important to know what the components do. What do those two resistors connecting the heater wires to ground do? What does the resistor going to the LED pilot lamp do? For two examples.
One can approach amp builds as paint by numbers, I guess. But knowing the basics of what the circuits do is far more satisfying and will keep one on the right path.
Trying to help, so please do not take offence.

No offense taken at all. The thoughts, suggestions, and tips are appreciated and welcomed.

You are certainly right. I do not know what these components do. I was trying to paint by numbers. I am going to learn these concepts prior to continuing this build.

I thought that I had the drawing correct by looking at Doug’s drawing and transferring that to what I was actually seeing in front of me. Since it is still wrong, I certainly have some work to figure out how to correct this.

[flyby71]

Doug's drawing is correct. Flyby's not so much. Same with the description. The two components labelled 47 are resistors, not capacitors.
And the two ends are grounded together, not just one of them.
The LBL is a great tool, if you have not heard of it I suggest that you have not done enough reading. That tool is everywhere here on the Forum.
And when building amps it's important to know what the components do. What do those two resistors connecting the heater wires to ground do? What does the resistor going to the LED pilot lamp do? For two examples.
One can approach amp builds as paint by numbers, I guess. But knowing the basics of what the circuits do is far more satisfying and will keep one on the right path.
Trying to help, so please do not take offence.

Just wanted to confirm with you…this drawing below is the one you are referring to that is incorrect?

[SEL49]

Just wanted to confirm with you…this drawing below is the one you are referring to that is incorrect?

This drawing is CORRECT.

[Willabe]

For this amp you want a 60w bulb for the LBL. You could use a 100w, but 60w will give a little more protection. 

Look in here;

https://www.sluckeyamps.com/misc/Amp_Scrapbook.pdf

[flyby71]

Just wanted to confirm with you…this drawing below is the one you are referring to that is incorrect?

This drawing is CORRECT.

Oh ok. I thought I had finally had it figured out correctly. Thank you!

[flyby71]

For this amp you want a 60w bulb for the LBL. You could use a 100w, but 60w will give a little more protection. 

Look in here;

https://www.sluckeyamps.com/misc/Amp_Scrapbook.pdf

Awesome. I will get a 60w. I already have my shopping list for Lowe’s tomorrow to build the LBL.

[AlNewman]

The 2 47R resistors connected to ground are called an artificial center tap.

Here's some reading until you get your LBL built.

http://www.valvewizard.co.uk/heater.html

[bmccowan]

This drawing is CORRECT.

My eyes see one resistor connected to ground - not both. The other resistor is only connected on one end. My eyes are old, so maybe I am not seeing the connection. There should be a jumper between the two turrets, eh?

[kagliostro]

@ bmccowan

There is a small white connection where you see nothing


@ flyby71

Go to

https://www.valvewizard.co.uk/ (the more the link on the left of the page)


https://robrobinette.com/How_To_Build_a_Tube_Amp.htm#google_vignette

https://www.aikenamps.com/index.php/white-papers

and read the more you can

after, download and read also this file

https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.trinityamps.com/ForumGallery/trinity/resources/geofex_tubeampdebug.pdf&ved=2ahUKEwiA9J2LnNmKAxUP2gIHHcuqENcQFnoECBIQAQ&usg=AOvVaw02SdjV5s6ficuuxTRabPQK

Franco

[bmccowan]

Thanks Franco - You are right, I could not see that line until I zoomed in on the image. All good.
Good reading list.

[JPK]

To me this is a perfect example of the difference between a schematic and a wiring diagram. The schematic is nice to understand how the circuits work, but doesn't depict actual wire routing and sequence of parallel wire connections. That is the lesson that I think you should learn here. What I've seen here is that Doug makes you think and makes you figure things out yourself [just my opinion]. I'm the same way. My kids used to hate it when I made them think while I helped them with their math and physics. I didn't just spoon feed them. That doesn't help anyone. It's always better to teach a man how to fish. Anyway good luck with your BJ build. Building amps is so fun.

[Willabe]

To me this is a perfect example of the difference between a schematic and a wiring diagram. The schematic is nice to understand how the circuits work, but doesn't depict actual wire routing and sequence of parallel wire connections. That is the lesson that I think you should learn here.

No, I think that's a little off. The layout drawing is for the (line) builder to know where to put what and so a repair man can find the parts in the chassis quickly. The actual wire routing just happens as part of the layout, but it's secondary. Some of it is  part of where the designer put what.

My kids used to hate it when I made them think while I helped them with their math and physics. I didn't just spoon feed them. That doesn't help anyone.

Yes, you have to teach people how to think for themselves, my father did that, my school teachers did that too, they used to do that in schools. Now they often tell you what to think. It's gotten very bad. I've seen many kids at a cash register that can't even make change without the register telling them what it is. It's based on a 100 scale! 

[flyby71]

I want to thank each of yall for the help, advice, learning material, and comments. I have a lot of great information that I have been reading on thanks to y’all’s direction.

It is satisfying to figure something out on your own. The lesson sure seems to stick more than just being told. I appreciate that.

I’m excited about the learning journey…..and the amp work is fun as well!

I’m going to continue on with learning the why’s and hows’s before I pick back up with the building process.

I’m sure I will be back to this thread with questions, but I hope to come back with a lot greater understanding of what I am doing.