Chassis

Developing the top layout.

I was able to work on the chassis this weekend, thanks to my good friend Matt, who has a garage full of tools. I probably finished about 2/3 of the work, with a few more cuts needed on the back panel, lots of drilling on the top, then assembly, sanding and finishing.

There were no real shortfalls on the part of the tools. The designer and craftsman, however, left a bit to be desired. I did ok on the table saw, cutting the sides at 45 degree angles and a shallow slot on the top to hold the aluminum. On the back side, I used a bandsaw to cut out what should have been a pretty easy shape to allow an aluminum plate for the backside components. But I wasn't really precise with my cut and it was sort of B+ work there (to use a tube amp voltage joke).



Pretty good cuts on the table saw.

On the front, I changed my mind mid-stream and altered the size of the panel that will hold the power switch and volume control. I thought that my original design didn't leave enough wood for good support, though as I thought about it later, it would have been fine. I had some complicated plans to use a router, and instead just drilled it out and used a hand jigsaw to cut out the rectangle, and then used knife and chisel to get the edges and corner pretty close to accurate (again B+ work).



Chisel work. Ugh.

On the top, I used a hole saw to cut out the openings for the larger output and rectifier tubes. I didn't have the right size for the smaller driver tube, so I drilled this out with the biggest drill bit I had, then used a round file to widen the opening slightly.

Overall I only somewhat enjoyed this part of the project. It helps to have the right tools, but for my next amp (oh, yes, there will be more), I will spend way more time on the design phase to make sure I have a really solid plan and the best visual appearance.




Couldn't resist a bit of wiring.

Large holes done.

Speaker Repair

Cleaning off the old decayed foam surrounds.

I was waiting for some other parts to arrive, so took a break from the amp and worked on speakers. I had some Infinity Reference Two bookshelf speakers that I bought 20 years ago when I went off to college and needed smaller speakers. They sounded great then, but the foam woofer surrounds had crumbled with age five or six years ago. After several unsuccessful efforts to get rid of them at garage sales for ridiculously low prices, they have been sitting in the garage, used mostly as sawhorses.

$20 on eBay got me some new foam surrounds, so I repaired one of the speakers the past few nights. It's a messy job, scraping off old foam and cleaning off glue. But not too difficult. Below is the updated speaker. I haven't fully tested it yet, just a low volume test with a small extra amplifier I have to see if it works. Seems to be fine and looks great! Seriously, folks, you missed your chance to get these speakers at my garage sale for like $6 for the pair. They are now back and ready for some good audio.



New foam added. Looks great!

More Board Components

I finished up most of the work on the board. I needed to add two coupling capacitors (I bought cheap ones) and a few resistors that I had missed in my last order of parts.

One tricky part was the constant current source IC (I have no idea what this really is) which has a heat sink on it and some really small connecting leads. I switched my soldering iron tip to the smaller point tip for this.

There are a few new parts not reflected in the instructions on the Tubelab website, but I found information on the DIYAudio forum about them. They are diodes for D3, D4, and an inrush current limitor in spot TR1. I attached these today, and then realized that the diodes were irrelevant because I'm not building this with the solid state rectifier. This would have required two other FRED diodes I'm leaving off. They were about $5 each and I figured I would rather start with just the tube rectifier and save a few bucks.

I also added all the connectors that will later be used to attach the transformers, input signal, switches, etc. The only one I left off was the connector for the rectifier switch since I'm not using this.

Maurice (my cat) just now got up after about a 3 hour nap in the shoebox I'm using to hold some tools. Seriously, how does he fit into that? It's like me taking a nap in the clothes hamper.

I'm thinking about some next steps. I bought an Allied power transformer which came in the mail the other day and ordered two Edcors for the output transformers. I have a few pieces of wood to start thinking about the enclosure and need to get a piece of aluminum for the top. I also ordered a speaker repair kit from ebay to fix up my old Infinity Reference Two speakers that I bought 20 years ago and the woofer foam disintegrated. Hoping these might still be good to use, and prefer testing with them instead of my Klipsch floor standing speakers that are in the living room.

Tomorrow is my son's 8th birthday party and I have a cake to go decorate in the form of a Minecraft Creeper.

Finished board bottom

Finished board top

Sockets and Capacitors

Added the tube sockets and capacitors tonight, most of them. I'm using the inverted assembly method in order to mount the board to a chassis and have only the tubes show through. Resistors don't matter because they are so small, but this impacted a few things in my component attachment today.

For the sockets, there are three octal and one noval socket. The instructions on the Tubelab website show how you can elevate the mini noval socket so it might be flush with the others when the board is mounted to the underside of the chassis cover. So I did this, using a small stack of Pokemon cards to get the right height to allow the connectors to just barely show through the surface of the board when I soldered it on. Even so, my noval socket is so much smaller than the octals though that I question if it will still be high enough. We'll see.

For the capacitors, I mounted them to the bottom of the board, and needed to ensure the correct polarity for the electrolytic ones. These have a stripe or other indicator to show which is positive and negative. Seems to have been pretty easy. The one mistake I made was that I ordered two of the capacitors rated at 85 degrees celcius, and the instructions recommend 105 to better handle heat of operation. I might replace these later, but thought it would be ok to proceed and hopefully this is just a matter of reduced capacitor life, not risk of explosion or other such deadly matters.

I do not yet have the coupling capacitors. I was going to order some nice Auricaps, but these were about $12 each, and I'm thinking I just want to get some sound out of this thing without spending a fortune, so I bought some cheaper ones and waiting for delivery. I also ordered my transformers today and that set me back around $140 including shipping for all three. I can replace the coupling caps later if desired to improve the sound.

Resistors!




My first component soldered on!

My solder came in the mail today, so after the kids were in bed it was time for my first good soldering session! I have used a soldering iron before, but never on a PCB and never with any sort of neatness or accuracy. But I've watched a few online videos and read some tutorials, and isn't that all any of us need to be able to accomplish just about anything in life?

After about an hour, I had soldered on all the resistors. Well, almost all of them. There's one that I accidentally ordered only quantity of one and actually needed two. And another one they were out of stock and I had to order in a second batch with some other components. But they are mostly all on.

The big resistor in R1 is temporary. The design is to either use this resistor or a power choke. I'll try this out with the cheap resistor first, make sure things are working, then remove it later and add the choke when I want the amp to start to sound better.


Good progress...

The tiny ones are not much fun to solder. They all look the same and are just little guys. I like the big ones! It's quite satisfying to see neat little mounds of solder flow through the holes.

I chose to use 63/37 solder, since I read that it is a little better than standard 60/40 in how it solidifies. To help as I soldered, I used two books as props to hold up the board (two favorites:  The Joy of Mixology and Intuition Pumps and Other Tools for Thinking).

I have a word document on my computer that I've copied the parts list into and I mark each one off with an X as I attach it. Also, best tip ever:  when I ordered the parts from Digikey, they let you add a customer part number to each item. Then the components come in little baggies with a label describing the part and also with your own part number on it. This made it really easy to go in order down the parts list and match components to the location labeled on the board.

I also have updated my workspace to now include an extra lamp sitting up on a can of paint, and a larger box for my cat to sit in.

Overall, soldering was easier than I thought. Of course, these are supposedly easier components to add! I'll do the tube sockets next time.




PCB with all the resistors (almost).



Workspace

I don't have a workbench. Every great hobbyist has one. I've taken over a table in our spare room, which my wife has designed as the creativity room, or craft room. There's a sewing machine, bins with markers and glue sticks, rubber stamps, wrapping paper, etc. Everything I'll need to make a tube amplifier.

Most of my phase 1 tools and components have already arrived. They came in multiple packages. I just love getting packages in the mail! I have only ordered some of the less expensive parts. That way if I get in over my head and need to give up, I won't have that much invested. As Homer Simpson once said, "If something's too difficult, it's not worth doing."

 

My workspace so far includes:

• A table with a cat on it
• A piece of foam board to protect the table from all the soldering marks I expect to make
• This computer to blog my efforts
• Coaster to hold each session's designated drink (an Old-Fashioned tonight, in honor of my good friend Ben, because it's his favorite drink)
• Some cardboard boxes with components and tools in them

Here are my starting tools:

• Weller 40 watt soldering iron (I had an old 25 watt Radio Shack one, but I run with the medium sized dogs now)
• A power strip to easily turn it on and off
• Diagonal cutters
• Small needle-nose pliers
• A few small screwdrivers
• Some sort of poking thing that came with the soldering iron, used to poke things
• Solder (I have lead-free, but I'm waiting on some nice 63/37 solder to arrive, so I probably won't use this)
• Desoldering wick, in case I mess up or need to remove some solder

And the components I'm starting with:

• Tubelab SSE board
• All of the various size resistors for the board
• The tube sockets (3 octal sockets and one mini noval socket)
• Most of the capacitors (I haven't ordered the coupling capacitors because these are more expensive and I'll probably put them on last)

So far, I'm in for less than $100 including the tools. Things will get pricier when I get to the transformers, tubes, enclosure and switches, etc.

Preamble

Here begins my DIY adventure to build a stereo tube amplifier. I have minimal electrical engineering knowledge. I've soldered a few things here and there, and understand which direction the batteries go into most of my kids' toys.

I've thought about doing this for several years, and after some recent browsing, I finally found what I think is the best option. I first thought I'd need a kit, where you buy all the components in a neat box with instructions, since I would not know what in the world to buy from an electronics retailer. Really, I don't know what those numbers mean on a capacitor...1500 uf, 50V, etc. And I don't know very well how to read a schematic, though I'm hoping to learn more through this process. But a kit really constrains you to a specific set of components and you have to sort of go all-or-none with it.

 

Then I found Tubelab, which I think is the best of both worlds--not a kit, but enough guidance that it's almost like one. George Anderson is a pretty amazing electrical engineer who designed several tube amplifier boards and includes part lists and complete instructions on his website (www.tubelab.com). I bought the Simplified Single Ended (SSE) board, which is good for beginners, but also designed well enough that I could put some decent transformers, capacitors and tubes on this to hopefully have a really good sounding, high quality amplifier (assuming I don't electrocute myself or wire it all up wrong and have it blow up). I'm sure some DIY audio geniuses would add in things like, "Yeah, it's two-stage and has this for biasing, and the B+ is so and so..." but I don't know what most of that means. But reading his website and the DIY forums gives me enough confidence that this will be a pretty good amp to build.

 

I'm mostly in this to learn new things, but also expect to have a nice sounding amplifier when I'm done, and do my best craftsmanship to have something that looks nice.

 

Here we go.