Scratch-building a tube power amp

Brian4561

Brian4561

Active Member
Now that I have a little tube preamp building experience under my belt, I'm starting to think about building a tube amplifier from scratch. I know its a huge step up in complexity, but its something I want to try.

It will also be a while until I actually start to build the thing. First, I have a Foreplay preamp kit that will be coming soon. Second, I'm planning that it will take some time to figure out what circuit to use, to have some knowledgable folks weigh in on the circuit plan, to source the appropriate parts for the build and to get a chassis figured out. That's why I'm starting now.

So where to start? I'm thinking I'd probably do a set of monoblocks rather than a stereo amp. My intent would be to run the kit preamps through the monoblocks. I'm not sure how much power I would want--with my current speakers, I don't know if anything under 30 wpc would work at all.

I'd also like to do a pretty high-quality circuit, one that has the possibility of doing some tube rolling and perhaps some later modifications.

So any suggestions on how I should start this process? What circuit should I look at?
 
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Look at some of Gary Kaufman's (simpler) projects: www.the-planet.org
and/or www.boozhoundlabs.com -- there is a bit of overlap :-)

Other good ideas can be found at Angela Instruments' site:
http://www.angela.com/catalog/how-to/

Consider getting a subscription to audioXpress magazine www.audioxpress.com

Also consider Pete Millett's little low voltage, hybrid headphone amp/preamp: http://www.pmillett.com/hybrid_head.htm
http://www.diyforums.org/millett.html

Dont' try to over-achieve on the first go-around!!

EDIT: A 30 wpc scratchbuilt ain't the place to start IMNSHO. If you really want that kind of power, you might want to start with the new Dynakit ST-70 www.dynakitparts.com

It's not too hard or expensive to BUILD some efficient speakers to start with a nice, low power SE or PP amp (Gary has examples of both at his site).
 
Hey-Hey!!!,
About simultaneously this is how I like to run a scratch build:

Pick a power tube. Expense, characteristics and availability all get consideration. Complexity of operation is another. There are good audio tubes that need 25A of heater current, so end use of the amp needs attention. A bedrrom system doesn't need a pair of 250TL finals and a 1k3V B+ I think.

Pick the general format. As in schematic, power level and parts sourcing for important stuff like output transformers.

Pick the front end tube(s). There are a few types that share one basing, with widely differing electrical performance that I like to play to. The front end valves need to play well with the finals. There is no sense trying to run an 845 from a 12AX7 with a 300V B+ to spell out an extreme example...:)

I like monoblocks. they're easier to carry around than stereo amps. Along this line, make them big. More room means easier modification later and it is easier to work on.

On your power level, it is a lot easier to build that power level with easily available schematics. A Dynaco Mk.III for example. However, if you're going to the trouble of building, consider that the schematic is one of the easiest things to acquire even if it is specially created for your project. No sense buiding what you can buy, in part I DIY because what I design and build isn't available at any price or in any store. You're building *YOUR* dream amp, yes?
cheers,
Douglas
 
Diving in on a scratchbuild first might be an exercise in frustration or maybe not. Like many, I started out by first repairing an amp & making it operable. Then later I modified it to where it barely resembled the original iteration. At that point I started feeling more confident and after a few more modding projects I built one from scratch. I was very lucky though in that I was surrounded by phenomenal technical resources. There were at least 8 people at my company into scratchbuilding amps, hotrodding existing gear, tweaking speakers, or earning a living off knowing how to do those things and I had a guardian angel every step of the way. If you weren't working there and asked me this question I would tell you emphatically to buy a kit, don't wing it. But then, that would be nearly 20 years ago and there were no internets & stuff.

Now is a different story. There are many sites out there such as diyaudio. AA, & here that literally put you in front of 100's of other builders, modifiers, romantics, charlatans, & seriously deranged audio lunatics. The toughest part will be determining whose advice to take and whose to ignore, not building a workable amplifier.

I say, go for it!

:thmbsp:
 
Hey-Hey!!!,
Building on Soundmotor's idea, it might be a good idea to transfer a vintage amp to a chassis big enough to esperiment on before taking a full scratch-build on. The additional room can be used for mods to the PS and the amp itself. You'll eventually discover that a vintage amp was built just as big as it had to be, and refined for the design that went into production. Stuff like that isn't the easiest to run Science Experiments on...:) which you'll need in order to do a thorough job on a scratch build.
cheers,
Douglas
 
Cool, that's a pretty good idea. That would give me a chance to learn a bit more before jumping in with both feet, so to speak.
 

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Finding a console amp to play with is an excellent idea. Low cost and they sound pretty good out of the box. The 6V6 is a great tube to start with

Then recap, tweak and improve, try a new input tube. Next you will be ordering up new output transformers and you’ll be well on your way…John
 
So what about the Dynakit amps? I see that Ebay sellers have all sorts of parts for the Dynaco amps-from PCB's to chassis and all that stuff.

Could I buy the bits and an instruction manual and build one of these for cheaper than buying a kit? Sure seems like it.
 
Brian4561 said:
So what about the Dynakit amps? I see that Ebay sellers have all sorts of parts for the Dynaco amps-from PCB's to chassis and all that stuff.

Could I buy the bits and an instruction manual and build one of these for cheaper than buying a kit? Sure seems like it.
Click to expand...

If you're ok with a few age spots( rust or its beginnings in the hazy chrome ), you can get an original St.70 cheaper than the new kits( maybe with a workable set of British valves too ). The instruction manuals are out there for the taking if you look.

Now if you need shiny chrome...:)
cheers,
Douglas
 
PakProtector said:
If you're ok with a few age spots( rust or its beginnings in the hazy chrome ), you can get an original St.70 cheaper than the new kits( maybe with a workable set of British valves too ). The instruction manuals are out there for the taking if you look.

Now if you need shiny chrome...:)
cheers,
Douglas
Click to expand...

Unfortunately, I don't know anywhere local to go about getting a ST70 that needs some TLC and the prices on that auction site seem awfully high. :no:

And I do like shiny. Or nicely finished hardwood. :D
 
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