[BurritoBeans]

Hello, and welcome to a thread that I was going to post six months ago but never got around to doing.

In this thread I'm going to cover how I built a pair of tube amplifiers, based somewhat on the original Fender Bassman schematics, and throw around some pictures. I really just wanted to outline the process of doing something like this as I thought it was a cool project and maybe someone else will find it interesting - I was thinking of maybe making a random series of building things like the amps, consolizing arcade PCBs, restoring some old stuff, and small hardware projects so this is a start anyways.

Something to note is that I’m not saying that everything I did was the best way to do it. I just like tinkering with hardware and by no means have any professional experience, just hobby restoration and construction mainly of HAM radio sets when it comes to tube-based technology, so if you know more than I do then please feel free to share some knowledge.

So, here’s a little table of contents
(all the headers will stand out so if you want to skip a part then just look for the next section)

• Why a tube amp?
  
• Picking a design
  
• Getting Materials
  
• Construction, Part 1 – Most of the Assembly
  
• Ironing out Mistakes
  
• Playing the amp
  
• Construction, Part 2 – Making some 4x10”s to go with the amp
  
• Conclusion
  

Why a Tube Amp?
So when I said that I was going to go for a tube amplifier, this is what I heard from most people:

“Why would you want a tube amp? The technology is outdated and costs way more! Why not just buy a modern amplifier and be done?”

Well, I’ve got a few reasons.

1. I like to play blues-y music with a more dirty sound to it and the tubes just fit the sound.
   
2. I always like messing with tubes in my radio sets so why not add them in somewhere else?
   
3. Yeah sure, modern modeling amps can do the same stuff but I just never find them to be that interesting.
   
4. I like building things! It’s the same reason I made my own CMVS and MAME cabinet instead of buying pre-made things and want to jump into a lot more projects.
   

So yeah, simplified it’s all just that great thing called Personal Preference

Picking a Design
Tube amplifiers have been made for years now – how did I find which one I would like?

To start off, well I went through and listened to a bunch of sample clips on youtube – different styles of play, different genres of music, and just different amps.

Now comes looking at schematics. Some things I considered included:

• How much of a pain does it look like it would be to build?
  
• How much documentation exists?
  
• Was it (or is it still) known for any specific issues apart from older capacitors degrading?
  
• What extra features and modifications can be added?
  
• Can I build it on fiberboard with turrets or eyelets?
  
• Can I make it work as a good practice amp but easily adapt it up to output a higher wattage if and when I get to play anything but bass or rythm guitar on stage.
  

And after all of that, I settled on the classic 5F6A Fender Bassman as my base. I like the tones, it’s been the base schematic of nearly every Marshall amplifier, and I mean come on it’s just a classic design. There were a few things I wanted to change – I wanted a gain knob, a effects loop for my pedals, and a headphone jack – and lucky for me I found pre-existing mods through some research and people like Rob Robinette which made my life easier. One layout in DIYLC later and we’re good to go.

Getttng Materials
So I have my pick of base design, I have my mods outlined, and I know what I want. Well that’s all cool, time to do the part which hurts – buying everything. Well, for the most part this is easy – pretty much just find stuff at the right tolerances, order an extra on all the cheap parts in case I screw up, and find an enclosure to slap it all in.

On the majority of components, well anywhere really works – I use Mouser myself but any big places had what I needed apart from a few suppliers not having the transformers and choke.

Tubes I was originally going to source some old stock off of eBay but after some thinking I just went with a new set of JJ tubes and used a spare Sovotek I had laying around. On the JJs, pretty much anyone supplies their stuff but I used Eurotubes as prices were a bit better.

On the enclosure, well originally I was going to build my own but I realized that it would be a bit wonky at best so I settled on a nice Hammond project box with a cut piece of aluminum and some rubber feet to go on the bottom.

Finally with the turret board, all I did was find the cheapest 10” long piece of 1/8” thick G-10 board and pack of non-forked turrets I could as I already have a setter and bit to put it all into place.

Wait a week for shipping and it’s onto the next step.

Construction, Part 1 – Most of the Assembly
Well, the parts are here so onto construction. Sorry for this one being so blurry but whatever, it is what it is.


The first step is to drill out and set turrets in the board – an easy but slightly tedious process, it’s just a case of marking where I want components to attach to and hammering turrets into said board – with a little time and making sure that stuff is sitting flat on the board it’s onto laying things out. A tip for if you ever do this -  make sure the turrets are flat on your board and hammer them in on a rubberized mat with some thickness as it will really help them go in. If you don't know or can't tell, what a turret board does is give you conductive posts sat into an insulating material, metal turrets on a fiberglass board in this case, for which you can route electronics - the system was made forever ago, it's better than blind soldering from point-to-point, and it's generally pretty durable compared to standard PCBs.


Now for the fun part, soldering the board together. This is simple enough – take the lead of the component, wrap it 2/3rds of the way around the turret, then put enough solder on to hold it together.

You can see that one capacitor is sticking up a bit, this is because I put the turrets a bit too tight for the specific one I bought. You may also see how messy my ground run on the one board is - trust me, the ground wires were fixed to be nice and neat. There's one red wire missing from the image but whatever, it's added in later - it goes from the big orange-ish resistor into the turret that makes the V-shape by the end of the board. Those empty turrets at the front are there for a diode rectifier - I wanted the extra tube and EZ81s are cheap so I didn't use this but if I ever get tired of EZ81s I can just make this in five minutes.


Now that the board is done, laying out the chassis was important. I got a 10”x3.125” piece of board so I was able to easily center that with quick math, then I had to figure out center lines and where to mount my external components. One really nice thing is that the plastic cover on the Hammond enclosure, there to protect it from scratches, makes a nice drawing surface for me to sketch stuff onto for drilling. I test fit the switches and potentiometers to make sure they fit and then mounted my tube sockets, transformers, choke, and terminal strip.


The board goes on and it’s time to connect from the board to the tube sockets, the transformers to the tube sockets and board, and the power socket to the system. I'll address it later but make sure to be smart when wiring in the main power transformer as if you mess up that's probably a good reason why tubes aren't glowing and your heaters are weak. This step took an extra two days as I realized that I didn't have rubber grommets that would fit my holes for wire runs between the outside and inside of the chassis - lucky for me Amazon Prime exists and kits of standard grommet sizes are pretty cheap. Again, on the wire runs, trust me these got a lot neater as time went on - this is all just a rough fit.


After that's all set up I added in the switches, pots, and input/output jacks - an hour of frustrating mounting angles later and I had the amps all wired up and ready for the first test.


Ironing out Mistakes
I messed up. Whoops.

Now, things getting into the signal are never good and one amp exhibited just that - on the mirrored board, because I mounted it the opposite way of the other board, had its filter capacitors (the big capacitors that stabilize the AC into a close-to-DC waveform) right under the big 270AX transformer and because of that were getting hit with the 480V DC and 6.3V AC signal, adding tons of fuzz - one board flip and re-soldering of every single wire later and this was solved, right?

No, it’s not... what did I mess up now? Well, another stupid mistake, on the stacked 1/4” jacks – the effects loop – I put wires to the wrong places, time to fix that. I realized that I could've probably used cheaper mono jacks instead of the fancy Switchcraft jacks that I had bought and this issue would've never happened but whatever, at least these have some element of quality to them.

So we're good now, right? Still nope, but this time on both amps. It turns out that me, not thinking about every single other multi-tube project ever, lazily daisychained the heater lines to the tubes instead of running them properly with the heater lines running one side on the 4 and 5 pins and other running on each 9 pin - I had wired one to the 4, one to the 5, and jumped the 4 to 9 at first. I realized that since it's 6.3V AC it makes sense that they need to be arranged like that, so yeah that was a mistake.

Construction, Part 2 – Making 4x10”s
Alright, so I want speakers for this as I don’t want to just feed into another amp and just using its speakers - time to make some speaker cabinets. My budget was running low on the project as I went for making two instead of one but this is fine. I didn't use the AlNiCo speakers like some people had said and instead went for a set of WGS speakers - they're usually cheap and fit the part for an amp like this anyways.

So I needed a cabinet design - well a bit of looking around and hey, some guys made Fender Bassman cabinets, too bad they cost $100 each unfinished on ePay so screw that idea. More google-fu later and I found just what I wanted, a nice little diagram with lengths and everything.


A bit of work with a table saw and dado blade, a jury-rigged router, a hammer, a disc sander, and some wood putty later they were done. Everything was janky but hey, at least it worked.






So yeah, woodworking is something I usually suck at but I can say that I’m proud of these – I didn’t take many* pictures building them but hey, at least you can see the (mostly) finished product. I still need a grill on the second cabinet but I'm still trying to decide on what cloth I want to use - whatever, that can be done whenever.

Conclusion
Here's the finished products





So yeah, that’s how my first amps were built. As I stated earlier I meant to post this about six months ago when the project was actually fresh in my head and I just finished it - if anyone wants any more information I'd be more than glad to give it.

If there's anything that I took away from this it's that even if I usually suck at woodworking and get a bit scared of larger projects, well it can be done with enough dedication to it. I'm usually lazy as all hell when it comes to projects outside of stuff for work so this was a lot of fun for me to complete.

So, I hope that you enjoyed reading through this mess or at least looking at the pictures.
-BurritoBeans

[mothered]

Goodness, this'll take a month of Sundays to read the lot.

I've read half of It, and I'm somewhat surprised with this comment:

by no means have any professional experience

I don't believe I've comes across pros who have this knowledge. Bookmarked and shall sift through the rest after today's outing.

[Vultra]

wow, this is good stuff. Great job mate.

[Percent]

This thread is massive! Thank you very much. I have a friend who is a guitarist, who I will be sure to send this thread to.