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6BM8 beginner tube amp video series

StepheK

StepheK

AK Subscriber
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I decided to do a full build video series on this little 6BM8 amp I designed. There have been some great tube amp build video series (blueglow etc) but none have been a beginner/cheap amp build like this. All in, with new high quality parts, this is a well under $300 build, and could be built with cheaper parts closer to $200. It is a simple design that shouldn't overwhelm a first time builder.

I'm going to post the videos as I go along and folks following need to understand some things may change in the design along the way. I may make some mistakes, I also plan to experiment with some things, but will be letting people follow along as I go, and share my thought process as I work through any problems I run into. At the end I will post the final schematic, with voltages and a BOM so people can build their own if they like.

Mark's Blueglow video of that KT88 build is what gave me the confidence to even try doing this, so I want to give something back, for people who may have less previous experience than I did, can give this a try. I'm not an engineer and try to explain in layman's terms my understanding on how this stuff works. I hope people enjoy this series and I inspire someone else to give scratch building a tube amp a try.


 
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Wonderful idea! I will be pleased follow along. Best wishes with your project!

Edit: I have now watched the first two videos and enjoyed them very much! Good job! It would make me very happy to see more women involved in our hobby, and perhaps your videos would mitigate some of the gender barriers.
 
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Those little Edcor's sound pretty good. If I hadn't spent extra on a fancy chassis, the 6LR8 amp I built using those Edcor's could have been built for right at $200 if I had used something like an 1/8" aluminum plate and wrapped in in some wood. I'm enjoying the show so far. Cool thread. :thumbsup:
 
I've been meaning to steer some effort towards a set of transformers I have for a low powered single ended amp. The tidy results others have achieved are inspiring, but the project que, is chock full.
Until some space opens up, I'll just be watching and collecting ideas.
I like that you are accomplishing it with very cheap, and basic tools. Tools everyone should have. It helps inspire confidence when you see others achieving great things with simple tools. Sure a cnc machine can make nice cuts, but most of us can't afford one and don't need one. Most households do have an electric drill, that's what I use too.
Keep up the good work.
 
trainbuftony said:
I've been meaning to steer some effort towards a set of transformers I have for a low powered single ended amp. The tidy results others have achieved are inspiring, but the project que, is chock full.
Until some space opens up, I'll just be watching and collecting ideas.
I like that you are accomplishing it with very cheap, and basic tools. Tools everyone should have. It helps inspire confidence when you see others achieving great things with simple tools. Sure a cnc machine can make nice cuts, but most of us can't afford one and don't need one. Most households do have an electric drill, that's what I use too.
Keep up the good work.
Click to expand...
A hand drill with several step drill bits with various step sizes are very handy. In many cases you won't need a big assortment of bits. I use them more often than my hole punch set. I use my hand drill and those bits much more often than schlepping a chassis out to the drill press.
 
Uploaded 2 more videos on the chassis fab work. I'm trying to show all the steps for people who have never done metal work before, so for folks who know how to center punch and drill holes, it might be kinda boring even though I edit out the repetitive parts. I decided to cut the fab stuff into short videos so people can skip ones they already know how to do. There might still be a tip or two in them though, or you might get a laugh out of me using a pair of dykes as a hammer lol.


 
Two more videos uploaded on the chassis metal work. I feel like doing the metal work is something that is daunting for many people, so I made multiple short videos with a lot of detail on how to do this with simple tools. I have no "workshop", just an old office desk and some basic tools most homeowners likely already own. The greenlee punches are probably the only real specific tools, and you can get around them using a step drill and a round file if you are careful.


 
I have a 1/2 ounce ball peen I bought from the snap on truck.
Far more useful than it looks.
Getting off my butt to go find it, however is a sure fire way to forget what the heck I was doing, so what ever is at arms reach will do!
Onward, forward don't step backwards!
 
Nice videos. They show ni
trainbuftony said:
I have a 1/2 ounce ball peen I bought from the snap on truck.
Far more useful than it looks.
Getting off my butt to go find it, however is a sure fire way to forget what the heck I was doing, so what ever is at arms reach will do!
Onward, forward don't step backwards!
Click to expand...
I lost a center punch that is spring loaded. Just press down and it sets it off making a dimple. I should get another.
 
Two more up. I like doing these as short videos, it allows me to continue working, easier to edit and upload etc too. This is the last metal work one.


This next is an important one, I discuss chassis layout, "rules" I follow about where to put certain things and how to avoid the always dreaded A/C hum in the design phase.

 
As I said in an early video, if you want to build this, order the output transformers now. Edcor is really slow delivering right now and expect it to take at least 8 weeks.

If you want to use the decorative tube socket mounting rings I am using for this build, you can order them here. These aren't required as they are totally cosmetic and a couple of button head bolts will work fine.

https://youdaelectronics.com/products/34mm-ring-washer-1

They have other colors and sizes here.

https://youdaelectronics.com/collections/tube-shield-ring-washer-364

They also have a nice selection of knobs. They are solid aluminum and are nice quality.

https://youdaelectronics.com/speaker-volume-knobs-c0367

I'm going to be using this one in silver, although any 6mm shaft size knob will work.

https://youdaelectronics.com/products/38x22mm-knob

I've ordered from these folks a couple of times and got good service.

Uploaded 2 more videos, then realized I am missing a couple of important parts (terminal strips) so will be a week or so before I continue. I might do one more on the few things I can deal with right now, like soldering the speaker jacks, while I wait. I do have the rest of the build mapped out, and think it's really going to look great when it's finished! Obviously I hope it will sound good as well lol.

I do plan to upload a final schematic with a BOM once it's all finished and I have the final tweaks done. Some of the resistor values will likely change to get the voltages right, plus I plan to try a few different cathode bias schemes and sound test them to find the combo I feel sounds the best, so you don't have to.


This 8th video is on powering up the amp and how to test that the heater voltages are in spec. So far so good!

 
In this video, we wire up the input and speaker jacks, cover some soldering tips and go over the rest of the component layout. I had to order some parts, so it will be a week or so before we continue on the construction.

I think it's good to point out there are many ways to do some of these things, and we all have our own quirky ways of doing them. I hope if people decide to build this amp, they make it there own by changing things around to their taste and intended use!

 
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