DIY Tube Amp

[scott spencer]

Hi all - I just finished up a guitar tube amplifier that I started close to 8 years ago for my boys who play. It's based on the classic Marshall 18 watt design, and is called the Hoffman 18 Watt Stout. It uses two 12AX7s in the gain stage, and twin EL84s in the output. This video clip is of it's maiden voyage...audio is isn't very good, and the amp is still in it's raw unfinished stage. It's got a nice tube sparkle and gets loud very easily...enough that they can play small local gigs with it. Sometime (hopefully soon) I'll put it in a box of some sort, and will label the knobs the inputs. My first thought was to build an old school carpenter's tool tote for it and call "The Toolbox", but we'll see.

For those of you familiar with this circuit, there's actually a spare tube sitting idle in an extra tube socket I installed....just in case I want to add a magic eye tube to it later on.

 

[Brent Dowell]

Very cool. I've got another friend who does his own amps. Can be a pertty serious hobby.

 

[Rob Keeble]

Wow this is very cool. I need to dig out my books. Thermionic valves (tubes) were the first formal electronic lesson i had back when Intel released the 8085 microprocessor. lol in the 70's

I remember clearly learning all about them and thinking what a waste of time and complaining to the head of department as to why we had to learn about outdated tech.

Subsequently took my students bursary and decided to invest it in a SDK 8085 Microprocessor development kit and self teach myself about microprocessors.

Never did i ever think these tubes would make a comeback. Great to see the full circle.

any link you can offer to where kits are available?

The cool thing is this amp would survive a nuke blast where other electronics that have not been radiation hardened would not.

If i recall correctly the Russians used mini thermionic valves in one of their fighter jets in the way past for this very reason. Just some useless info.

Great amp and project thanks for sharing it and bring back the memories.

 

[scott spencer]

There are plenty of websites and forums with good tube info, along with some moral support. Not too hard to do if you can read schematics and solder. I got into tubes back in my highend audio and speaker building days....the best high end stereo sound in the world is still tube based IMHO (ie: Convergent Technology).

http://el34world.com/ (forum, schematics, parts, and kits, pics, sound clips, etc)

http://ax84.com/

http://ampgarage.com/forum/index.php

http://www.diyaudio.com/forums/tubes-valves/

http://www.mojotone.com/kits

http://www.tubeampdoctor.com/en/shop_TAD_Amp_Kits/

 

[Vaughn McMillan]

Very cool, Scott. I remember when you first started talking about building an amp.

...Never did i ever think these tubes would make a comeback. Great to see the full circle...

In certain markets, tubes never left. Most guitar players favor tube amps, and like Scott said, lots of high-end audiophile amplification is done with tubes.

I play with a solid state guitar rig, but what makes it superior to any other solid state approach is the accuracy with which is mimics a tube amp circuit, from the properties of the tubes to the other individual components like capacitors and resistors. Also important is how the various virtual components interact with each other. And it's easy to swap stuff around. I can put a '59 Fender Bassman tone stack on a modern Mesa Boogie amp. Or change out the 6L6 tubes for 12AX7s. Although it's impossible to quantify, most players can't tell a difference between a good amp modeler and the real thing in blind tests. (And I appreciate the fact that I can bring the equivalent of 250+ different amps and over 1000 speaker cabinets to a gig, all in the space of a 2U rack-mounted box.)

 

[scott spencer]

I remember you mentioning how much you liked your solid state modeling amp before. I think one of my boys had a cheap Crate practice amp that said "modeling amp" on it, but it wasn't very good quality and not very sophisticated like yours. Maybe it's the glow in the dark factor, and/or the fact that my dad used to fix vacuum tube televisions and stereos when I was a kid, but there were always tubes around so I just gravitate to them. I'll just be happy if he plays enough to get better on the guitar!

 

[Vaughn McMillan]

I've still got three tube amps, including the Fender Deluxe Reverb my folks bought for me when I was in about 6th grade. I love them, but like the versatility of the modelers, and the ability to get a good overdriven sound at lower volumes. I think a project like yours would be fun, whether it was used for gigs or not. Bonus for you is that your boys have an amp they'll cherish forever.