Just starting my Blues Jr. III project

[Tbone55]

Well, I just started working on my Blues Jr. III amp rebuild. It's  a nice amp and sounds decent enough but I just can't stand the inside looking more like a computer than an amp. It has the potential to be so much better and Doug's kit is just the ticket. I'm going to try and document as much of the build as possible and hopefully this will help others down the line. Here are some of my initial steps. I wanted to post some photos but they appear to be to large to post.

1. Inventory all parts that came in the kit.
2. Measured all resistors to verify values.
3. Placed the resistors and capacitors on a board clearly marking their values.
4. Bagged remaining parts into groups, clearly labelled

As per Doug's advice, I plan to take it slow and easy. Steady wins the race.

Thanks and stay tuned. I'm sure I'll be posting questions.

[vampwizzard]

Those seem to be good, practical steps. As a relatively new builder myself, this is a great, supportive forum with lots of knowledge floating around. Looking forward to the progress updates.

[nandrewjackson]

Slow and steady, it's all in the details. 


If you're using google drive or something similar, post shareable links to your pictures in your posts here.


 

[Tbone55]

Those seem to be good, practical steps. As a relatively new builder myself, this is a great, supportive forum with lots of knowledge floating around. Looking forward to the progress updates.

Thanks. I'll try to post some pictures as soon as I figure out how to resize the files. It's definitely important to take small steps and review what you've at each stage. As Doug said, if you do everything the way it should be done the amp should work. If it doesn't you've gone wrong somewhere.

[Tbone55]

Slow and steady, it's all in the details. 


If you're using google drive or something similar, post shareable links to your pictures in your posts here.


 

Thanks. I may have to do that. Appreciate the response.

[Tbone55]

Here are some images of the build so far. This is the first time I'm trying to share photos through Microsoft One Drive so I hope it works. Here's the link.

https://1drv.ms/f/s!AloVFOBmUO_sa35nFBYztVTNpV4

My next step will be to drill the holes in the board and the chassis. I think I've located the chassis in a good location but please let me know if there's a better spot. I'll wait to hear back before drilling the holes. You can see in the images where I've located the board and marked out the holes. Take a look at the difference between the original output transformer and my replacement. I'm using a Hammond transformer that is a replacement for a Fender Deluxe Reverb amp. I just have to drill another hole to mount it because it's bigger. A lot more options for wiring speakers, hope I can figure it out.

[Slimtim]

pics look great.good luck with your mods.measure and measure some more,dont wanna do redos or do overs.

[Tbone55]

pics look great.good luck with your mods.measure and measure some more,dont wanna do redos or do overs.

Thanks. Will definitely be double checking everything as I move along. More pics to come.

[jamaio]

On my Blues Jr conversion I mounted the board about ¾" from the edge of the chassis. Looking at the pictures Doug has posted in the build section, he has the board closer to the edge of the chassis similar to your layout.

As long as there are no clearance issues or conflicts with mounting the OT you should be good.


Edit:  Just looked at the pictures again, the way you have the board positioned is backwards. The Caps need to be near the PT.

[Tbone55]

On my Blues Jr conversion I mounted the board about ¾" from the edge of the chassis. Looking at the pictures Doug has posted in the build section, he has the board closer to the edge of the chassis similar to your layout.

As long as there are no clearance issues or conflicts with mounting the OT you should be good.


Edit:  Just looked at the pictures again, the way you have the board positioned is backwards. The Caps need to be near the PT.

Thanks for your input. I placed the board temporarily that way just to get an idea of the location. I went with Doug's placement based on the images in his instructions. The OT is mounted now and I've drilled the holes in the board and chassis. Finished lacing up the turrets but have to buy some solder to finish the job. Also put the tube board together as well. Will wire the filaments as well when I get my solder tomorrow. Will post some pics soon.

[jamaio]

Sounds like you are off to a good start.

I made a few mistakes along the way, I looked at Doug's picture of the under board jumpers and matched mine exactly. After I thought my build was complete, when I started to adjust my bias I had no voltage reading. On Doug's first board he has the bias pot on a separate board, hence the missing jumper. I did not want to remove the board so I ran a jumper on top the board, no one will ever notice!! There was another ground I missed and my ground bus on the back of the pots broke. The break in the ground bus was a hairline fracture that I could not see. Everything worked great on my bench, then when I installed the chassis in the cabinet I had no sound at all. I took the chassis out and on my bench it started working again. It took me a while to find the broken wire, I poked everything with a wooden dowel while injecting a tone. My amp sounds great now and has preformed well for the past 2 years.

Look forward to seeing more pictures of your build.

[Tbone55]

Thanks, looks like Murphy's law paid you a visit. I'm hoping to avoid that but the best laid plans........you know how it goes. I'm keeping a log of each step as I go along to keep me on track and to hopefully help me review my steps. If I run into any problems during a step I can make a note of it. That way it might help troubleshoot problems down the road. Before I laced up the board I assigned a number to each group or pair of turrets that required lacing. As I did each lace I ticked off that group of turrets then used my multi meter to check for continuity. Now I know I have the turrets laced up right. After I solder the turrets I'll check for continuity again. Yes it is tedious but if you go along and just assume that everything's connected properly, well,, that's when good old Murphy comes along. It doesn't mean that I still won't encounter a problem, but maybe just one less to deal with. That crack you had is a perfect example.

Cheers!

[sluckey]

Here are some pics that show how I deal with lacing the board jumpers and installing under-board jumpers. I use a highlighter to keep up with jumpers on complicated boards. There are three pics on this page that deal with board jumpers. May give you some ideas. BTW, the highlighter method also works well for installing components and board interconnecting wires.

     http://sluckeyamps.com/VAC15/ac15.htm

[Tbone55]

That is one hell of an Amp. What I'm doing is amateur hour in comparison. Beautiful work! As per your example I used a highliter to mark the underboard wires. Double checked each one afterwards. The wiring for this board changed due to the bias pot being added so there were a couple of wires in different places. I used a white wire for the bias pot connection as the original example provided by Doug (Blues Jr conversion) didn't show this wire.

Thanks for your post. Hope to hear from you when I have questions.

[Tbone55]

I have a question. The tube board for this amp that I see in Doug's conversion has turrets located at the one end to attach two  47 ohm resistors to but the tube board I received has eyelets, fairly large. Is there any advantage either way?

Also, with the resistors installed, what should my resistance reading be from the outer lug to the outer lug? I'm expecting to read the total of the two resistors (94 ohms) as they are in series but that's not what I'm getting. Did I possibly damage the resistors? I'm only reading 23 ohms.

Thanks.

[sluckey]

I have a question. The tube board for this amp that I see in Doug's conversion has turrets located at the one end to attach two  47 ohm resistors to but the tube board I received has eyelets, fairly large. Is there any advantage either way?

I don't know why Doug changed to eyelets, but I suspect it has something to do with mounting the tube board. The eyelets are lower profile which would allow the board to be mounted with shorter standoffs, possibly allowing tube shields to be used. Why not ask Doug? Here's a link that shows the newer boards with eyelets...

     http://el34world.com/Hoffman/Blues_Junior_Tube_Board.htm     

Also, with the resistors installed, what should my resistance reading be from the outer lug to the outer lug? I'm expecting to read the total of the two resistors (94 ohms) as they are in series but that's not what I'm getting. Did I possibly damage the resistors? I'm only reading 23 ohms.

Outer lug to outer lug would be 94Ω, but only if you don't have the filament leads connected or tubes plugged in.

[Tbone55]

Thanks Sluckey,

I had the tube board info printed out but didn't notice the image was the same as mine. I've got all my information printed out but I think it's information overload in my case. The larger eyelets will make it easier for soldering the 6.3vac leads from the PT to the board.

As far as the resistors go, is it because the filaments are open at the end of the run to the pre-amp tubes that I can't get a proper reading? You've confirmed the resistance I should see.

Thanks.

[sluckey]

Do you have tubes plugged into the board? Do you have any wires connected to the board?

[Tbone55]

Do you have tubes plugged into the board? Do you have any wires connected to the board?

Yes, I have the tube board wired up with the tubes installed.

In the meantime, here is a link to some more pictures I took of what I've done so far. I wired up the V2 preamp tube as Doug did to get more push from the tube. My understanding is that only half of the tube is actually being used in the original design. I didn't wire it up exactly the same way as Doug did with very short pieces of connecting wire. I did one connection the same way but the other two I ran the wires around the outside of the ceramic base. You can see it in one of my pictures. Should I have just used really short jumpers or is the way I did it ok?

I believe the next step will be to install the turret board and connect the transformers as well as the speaker jack and the footswitch jack. Also have to hook up some ground connections. Don't want to forget those!

Cheers!

https://1drv.ms/f/s!AloVFOBmUO_sa35nFBYztVTNpV4

[vampwizzard]

This meticulousness may be overkill for smaller amps but absolutely necessary for any level of complexity in future electrical work. Im jealous of your work habits. Super impressive.

As far as longer leads go.. you have to balance ease construction with length of conductors. In signal wire, length of unshielded wire starts introducing noise into the circuit. Im pretty sure youll be ok here, but wait for more knowledgable critique.

Keep it up! looking forward to more pictures.

[sluckey]

Your way works too. Doug is the master. I do it his way. I remove that center shield pin on my sockets specifically for putting jumpers between tube pins. Here's a pic with cross jumpers on three sockets...

     http://sluckeyamps.com/dual_lite/big_guts.jpg

[Tbone55]

This meticulousness may be overkill for smaller amps but absolutely necessary for any level of complexity in future electrical work. Im jealous of your work habits. Super impressive.

As far as longer leads go.. you have to balance ease construction with length of conductors. In signal wire, length of unshielded wire starts introducing noise into the circuit. Im pretty sure youll be ok here, but wait for more knowledgable critique.

Keep it up! looking forward to more pictures.

Thank kindly. I'm trying my best not to run into problems down the road. Appreciate your input.

[Tbone55]

Your way works too. Doug is the master. I do it his way. I remove that center shield pin on my sockets specifically for putting jumpers between tube pins. Here's a pic with cross jumpers on three sockets...

     http://sluckeyamps.com/dual_lite/big_guts.jpg

Thanks kindly. I didn't realize you could remove the center shield pin. I don't know what that center pin is for but if I did I might have removed it. I'm still trying to learn more about how tubes work as well as how the whole circuit works. Hope to be sending more pics later today after I've worked on the amp some more.

[sluckey]

That center pin is usually connected to ground and serves as a ground shield as well as for connecting some components from tube pins to ground. It's very useful in radio frequency circuits but not needed at audio frequencies. I just use a Dremel with a cone shaped grinder to remove them. I've heard that sometimes those center pins are holding the socket together but I've never seen one like this. Should be easy to determine with a quick look. You can even remove them after the socket is wired but you must use a steady hand.

[Tbone55]

Thanks, I may remove that center shield pin later on. For now I'll leave it as is. Hopefully it won't cause any problems the way it is.

[Tbone55]

Bit late posting my update of the build. I finished hooking up all of the tube sockets to the board, installed the filter caps, bias resistor, bias diode, bridge rectifier. Hooked up the output transformer, power transformer, ran all of the grounds. I had to extend the a/c leads of the PT that go to the bridge rectifier because they wouldn't reach. I used automotive wire of the same gage (copper stranded) but I'm now wondering if it is good enough to use for this. The leads of the PT said the wire was rated for 600V, the automotive wire only says 60V. Does the rating have to do with the ability of the covering to not get burned through by the voltage pressure?  I'll get some proper rated wire and replace these. The speaker jack is all hooked up as well. The other input jack next to it was for hooking up a footswitch to turn the FAT switch on and off. I haven't hooked this up yet.

Next step will be to install the remaining components onto the board, then hook up the pots to the board. In one of my pictures you can see the names of the components that have already been installed written on some masking tape. Some that I installed aren't there because there are others with the same values that still need to be installed. When all of them are installed I'll put a piece of masking tape with their value and quantity on my wooden board. The one thing I kept checking for was continuity wherever possible after soldering my connections. This should help weed out any bad connections up front rather than trying to chase them down afterwards. It may not guarantee it, but should help reduce problems of this type.

Here's the link, https://1drv.ms/f/s!AloVFOBmUO_sa35nFBYztVTNpV4

Suggestions and comments are greatly appreciated. 

[sluckey]

The other input jack next to it was for hooking up a footswitch to turn the FAT switch on and off. I haven't hooked this up yet.

That's a bad location for that footswitch jack. I really don't think you'll be using a FAT footswitch but if you must have one, move it down near V1.

[Tbone55]

Thanks for the reply. I don't think I'll be using the FAT switch either. I've already installed the mini-switch for it on the faceplate but haven't hooked it up to the board. For now I think I won't wire up the input jack. Would you mind telling me why this isn't a good location for it?

I have another question regarding hooking up the OT transformer leads to the power tubes. Does it make a difference which colored lead goes to each power tube, pin 7? The schematic shows the blue lead going to V4 and the brown lead going to V5. If this is reversed, will it cause a problem?

Thanks.

[sluckey]

It's always a good idea to keep preamp stuff far away from power transformers, power amps and other noisy high current components.

It does make a difference which OT leads connect to the power tubes in an amp such as this that has a NFB loop. Get'em wrong and the amp may squeal, howl, or just have other odd sounding symptoms. And you can't know for sure which is the right way, so it's best to not trim the leads to length until you can turn the amp on and test it out. If you need to swap them you will have enough length to do so.

If you have already trimmed them to length, don't panic. You have a 50/50 chance of having it right.  But if not there's another easy way to accomplish the same thing. We'll talk about it more when/if a swap is needed.

[Tbone55]

Okay Thanks. I have the correct colored lead hooked to the correct power tube according to the schematic. Guess we'll find out soon enough if it's gonna work.  Do you think I'll have a problem with the wire I used to extend the a/c leads going to the rectifier? I had mentioned it in the earlier post.

Cheers!

[sluckey]

Probably not. I would not put any auto wire in my amps though.

[vampwizzard]

A bit about conductors: You size the conductor to deal with how much current it can handle, and you use insulation rating to deal with how much voltage you need to handle. I had never really seen 60V wire but it makes sense in mostly digital or super low voltage situations like cars and solar (48V systems max) vs the NEC classified "Low Voltage" systems typically designed up to 600V like most wire we use for amps (but goes up to 1000V in the code).

What happens when you exceed the voltage rating is that you lose the insulation properties and it basically becomes bare wire. When you exceed the current rating you get a fun fire starter/wire melter.

Youre going to need 600V rated wire most likely. Even if the 60V wire works, thats pretty darn precarious.

[Tbone55]

A bit about conductors: You size the conductor to deal with how much current it can handle, and you use insulation rating to deal with how much voltage you need to handle. I had never really seen 60V wire but it makes sense in mostly digital or super low voltage situations like cars and solar (48V systems max) vs the NEC classified "Low Voltage" systems typically designed up to 600V like most wire we use for amps (but goes up to 1000V in the code).

What happens when you exceed the voltage rating is that you lose the insulation properties and it basically becomes bare wire. When you exceed the current rating you get a fun fire starter/wire melter.

Youre going to need 600V rated wire most likely. Even if the 60V wire works, thats pretty darn precarious.

Yep. Totally agree. I'm not going to take that chance. Will be buying some today. Thanks!

[EL34]

I have a question. The tube board for this amp that I see in Doug's conversion has turrets located at the one end to attach two  47 ohm resistors to but the tube board I received has eyelets, fairly large. Is there any advantage either way?

It says this on the library page

Note: When assembling the Hoffman Turret boards, use the documents under each board
Do not use my builds below to assemble a Hoffman board -(my picture builds)
You may look at my builds below as a rough reference only
Things always change after I do a build
That's why I do these test builds first

You use the documents for this build here to assemble
https://el34world.com/schematics.htm#Hoffman_Pro_Junior_Conversion

[Tbone55]

Hi Doug. Please clarify something for me. Shouldn't  I be using the Blues Jr. Conversion, not The Pro Junior Conversion Instructions? I referred to your Blues Jr conversion, the Hoffman amp build instructions, the Blues Jr tube board instructions as well as all of the layout, schematic, hook up tips and one other pdf for my build.

Thanks.

[EL34]

Hi Doug. Please clarify something for me. Shouldn't  I be using the Blues Jr. Conversion, not The Pro Junior Conversion Instructions? I referred to your Blues Jr conversion, the Hoffman amp build instructions, the Blues Jr tube board instructions as well as all of the layout, schematic, hook up tips and one other pdf for my build.

Thanks.

There is no Blues Jr instructions or Pro Jr instructions
Did you read the very top lines of the Install Instructions?
https://el34world.com/Hoffman/instructions.htm

see the screen shot below

[Tbone55]

Yes, I did. Those are the instructions I used. I used the Blues Jr conversion you did as well, to see how you positioned the board, ran the wires and what color wire you used for the hookups. It was a good visual aid. I've been very meticulous in my build and layed out a step by step process which I have been documenting from the start as well checking and double checking my work. As you said, if everything is done right the amp should work. I totally agree.

Thanks.

[EL34]

Yes, I did. Those are the instructions I used. I used the Blues Jr conversion you did as well, to see how you positioned the board, ran the wires and what color wire you used for the hookups. It was a good visual aid. I've been very meticulous in my build and layed out a step by step process which I have been documenting from the start as well checking and double checking my work. As you said, if everything is done right the amp should work. I totally agree.

Thanks.

I was answering your question about different sets of instructions for different boards
As it says at the top of that document, the instructions apply to all my boards

[Tbone55]

Understood.

Thanks.

[Tbone55]

A new update in the build. I'm getting so close to the finish line. Here's a link to some pictures of the build. When soldering the components to the board I used both the layout diagram and the schematic as a cross reference to make sure I put the correct component in the correct place. I also checked each of the components off of the BOM as they were installed. This just verified that I had used all of the components and didn't wind up with "extra" pieces at the end that shouldn't be there. Next it's time to hook up the POTS to the board.

I do have a question. I bought some wire to extend the leads of the Power Trans high voltage output (256vac) that goes to the a/c leads of the diode rectifier. I bought the wire on line as I didn't want to buy a 100ft reel at my local electronics supplier. The information stated that the wire was rated for 600v, 200c temp and that the insulation was silicone. Now that I received it, nowhere on it does it say 600v, only the gauge and temp rating. Shouldn't the voltage rating be on the insulation? I don't feel comfortable using it. Any thoughts?

here's the link: https://1drv.ms/f/s!AloVFOBmUO_sgRJCbOOHP-Gm2Kmn

Thanks.

[Tbone55]

Well, I just finished up the conversion. Now it's time for the true test but I won't be doing that tonight. Time to rest a bit and do a bit of reading about firing it up. If anyone has any advice on this I'd appreciate it. I've attached a link to the finished amp.

https://1drv.ms/f/s!AloVFOBmUO_sgRjOdl-pxidGC5L5

[Tbone55]

I've been reading the information on firing up the amp for the first time and it seems that I should have been doing some testing at certain points in the build. I'm going to make up a current limiter before doing anything else and would like some advice. Should I unsolder my PT and OT leads in order to check for the output voltages at the secondary sides or would it be ok to leave them hooked up while using the current limiter? I'm going to go over the circuit again and double check the wiring and resistor values but don't have the capability of measuring capacitor values so I'm going by the values on them and comparing to the layout/schematic/BOM. I'm pretty confident that I've hooked everything up correctly but want to be cautious at this point. Any and all advice would be greatly appreciated.

Thanks.

[Tbone55]

I've gone through everything once again from the very beginning, the turret board lacing and jumper wires to all of the tube connections, component connections, pot connections, jack connections, transformer connections and power on/off switch. Good thing I did to because I found two capacitors that were located in the opposite locations they should have been. Everything else appears to be in the correct location and the connections appear to be solid. I also checked the ground connections and they all show 0.1 ohms resistance. I'm now ready to make the current limiter to use for the start up. All tubes are removed. It certainly paid off re-checking everything again. Not sure whether I should unsolder the PT & OT output leads to test the transformer voltages.  I guess if I have enough confidence in my work it shouldn't be a difficult choice. 

[Papa Jim]

That looks like you are doing a super nice job on it. Keep us posted on the completion.

[sluckey]

Not sure whether I should unsolder the PT & OT output leads to test the transformer voltages.

I wouldn't

[Tbone55]

That looks like you are doing a super nice job on it. Keep us posted on the completion.

Thanks! I certainly will.

[Tbone55]

Not sure whether I should unsolder the PT & OT output leads to test the transformer voltages.

I wouldn't

Yeah. After some more thought I don't think I will. I think I've done as much as I can to eliminate any errors. Need to be confident.

[Tbone55]

That amp looks GREAT. It would be nice to have a variac, but one idea is to plug your current limiter into another amp or device that draws similar current first. This way you know what to expect. Mine didn't work right at first so it was a WTF moment instead of cool voltage readings. Once again NICE JOB!

Yes it would but I think I've done as much double and triple checking that I can and I have to have some confidence in what I've done. What was the problem you ran into?

Thanks.

[Tbone55]

The current limiter itself. Fire it up man! You've put in the time. I was just referring to know what the dim bulb will look like when you do.

Well, I do have a solid state amp I could use but would that be the same as a tube amp?

[Tbone55]

The current limiter itself. Fire it up man! You've put in the time. I was just referring to know what the dim bulb will look like when you do.

I have a solid state amp. Would that be the same as using a tube amp?