Homemade amp...why not? (contains cheating)

Tomas

I really like 30s style amps like Stimers. But they are too expensive for me in these days. So I decided "make" my own for my Kleio 47. Plan was easy. Buy some wooden box and some second hand tube amp and use amplifier and speaker from it. Hmm..no that's not me. I like things a little bit more complicated. So I bought 12mm plywood, Jensen neo 10/100, Mooer little monster AC and lot of small retro things like nice textile grill. My inspiration were some kind of combination of Nuance amp and Stimer M6. And fun can start. Yes..all things together weren't that cheap as my first plan. But...but..so what. I love projects. I'm not joiner, but I work with wood solutions, so if something, finish should be nice...hope. I don't know anything about guitar amps. I never had one..like proper one. So any advice is welcome. Like...do anybody know, how dangerous is having neodymium speaker over the hot tube amp? I heard that neodymium have this weakness with heat. I consider some extra isolation. And should I change china 12ax7 for something else like 12ay7 or just different brand? For start I share some first photos with you. In the future I will posts another's. Thanks for reading and wish you beautiful day!

BillDaCostaWilliams

Looks like a fun project.

Buco

Your cabinet work looks amazing. Obviously you're not a novice at this. Can't wait to see the rest of the process and results.

Tomas

@Buco Thanks! Actually it is my first box or anything like that I ever made. So thanks Buco! :D I did some work from wood in my past, but this is maybe my best result. But I have luck that I can use some tools at work, one friend with experience and of course lots of videos on youtube. Just now I finished the lacquer!

nomadgtr

Your instincts on the preamp tube are correct. Try something with less breakup like a 12au7. The Stimer M12 amp uses that and a pair of EL84s in the power section.

Have you seen the new Supro Delta King 12? It has a single 6L6 in the power section and single 12ax7. I'll bet if you just swapped out the 12ax7 with a 12au7 you would get in the ballpark for fraction of the price of a Stimer.

https://www.suprousa.com/amplifiers/delta-king-12/?sku=1822RTB#specs

Tomas

@nomadgtr This amp look's pretty good. Lots of power. What does it mean that "gain rating" or "less gain" In different tubes. Does it mean it will have less overdrive in the same volume. Will be different loudness of the amp? Will be the characteristics of the sound different? I never had any tube amp and I'm confused from internet informations. I just looked to nuance amp and find amp with the same tubes, because I liked the sound. And mooer have sound similar to vox ac30 witch a few jazz guitarist use. That was my thinking...

scot

Amps like the Stimer M6 or this Supro Delta 12 are class A amps, which basically means the single output tube conducts all the time, and amplifies 100% of the input signal. This is like a Vox AC4 amp. A good Fender amp, for example a vintage Princeton Reverb, is class AB which uses 2 output tubes, each amplifying slightly more than 50% of the input signal. These tubes do not conduct in the absence of a signal, giving a much longer tube life and cooler operation. Class AB amps contain more harmonic content in the amplified signal, giving the "fat" tone associated with Fender amps, while a class A amp has a sharper, more immediate kind of sound, probably because the tube is already conducting when the signal is applied. Most modern amps like a Blues Jr also use a solid state rectifier instead of a tube, which some people hear more than others. I have a much-modified'68 Princeton Reverb, but like the Blues Jr just fine too. Some larger Fender amps also allow for different rectifier tubes to change the plate voltage to the tubes - so clever!

I have built, repaired and modified all sorts of amps, pedals etc, since I was a teenager. Anyone with questions, feel free to DM me, I'll answer any questions if I can, and will not BS you if I can't.

These two websites offer basic info re amp theory and operating classes

https://www.electronics-tutorials.ws/amplifier/amplifier-classes.html

https://www.mojotone.com/support/knowledge/Class-A-Amps-What-They-Are-and-What-They-Are-Not

Schematics and kits for nearly any kind of amp are easily available.

Buco

As simple as your question seems, the topic is a very complex one. I only understand general concept of tubes today. I knew much more when I went to school and studied it in the high school but never worked in the field of electronics so all of that knowledge mostly fizzled out. My advice is, find a simple and tried design and build it as designed when it comes to the choice of tubes. Then you can get a few different preamp tube types and hear what it does to the circuit of the amp and how that affects the tone. You'll learn a lot as you're building the circuit. It will become much more clear how the signal travels and what happens during the path and your understanding will multiply. Then you can teach us :)

PS there's is a good video in this article to demonstrate how different preamp tubes behave in the same circuit:

https://blog.thetubestore.com/preamp-tube-gain-tweaking/

Lango-Django

Tomas, I am a fellow lover of the vintage look and I, too, like to create things.

About ten years ago, I had a similar idea to yours... I was too lazy to construct a whole new amp and cabinet like you are, but I wanted to give my amp a vintage Art Deco look.

So I made a three-sided wooden box to put my small Mini-Loudbox amp in, which also served as both a music stand and a carrying cart for my amp, guitar and banjo.

Unfortunately, the whole creation finally proved to be way too heavy to be practical for taking to gigs, but I still have the template I made for the front grille of the cabinet, based upon the old UK Pye "rising sun" style radio grilles of the 1930's.

My creation looked really nice with beautiful wood veneer on the front. And for speaker cloth, I found a brown tweed fabric as similar as possible to the ones the old radios had. The diameter of the circle above is about 46 cm.

If my template would be of any interest to you, I would be happy to fold it up and put it in a big envelope and mail it to you in the Czech Republic... please PM me if interested.

Regards,

Will

PS Here is the design I copied mine from... interestingly, in my research I learned that this beautiful "rising sun" design was immediately discontinued by the Pye radio company in 1939, when the UK went to war against Japan...

nomadgtr

Hi Tomas,

Think of gain as output power. If you look at the 12AX7, 12AT7, 12AY7 and 12AU7 as a family they are differentiated by their output. What that means to you as a player is that the 12AX7 starts to distort sooner than the 12AT7 which in turn starts to distort sooner than the 12AY7 and so on. So by now you're probably thinking that this is a simple choice right? Well there is a caveat, you also see a drop in volume with these along with the drop in distortion. So a 12AU7 won't be nearly as loud as as 12AX7 either. You can make up for some of that in the power section though. What you don't want for our genre is an amp that distorts too soon before you reach the desired volume.

So, back to your build. If you're wanting to keep the distortion to a minimum you have a couple ways to go. You can stay with smaller wattage and use a 12AT7 or 12AU7 in the preamp with the tradeoff in volume. Or, you could go with a little higher output wattage say 15-20 watts or so and keep a 12AX7 in the preamp. With the higher output wattage you can get higher volumes before it starts to distort on you. It really depends on preference and usage. There is no right answer, just your preference. How loud do you need to go is the question? When I need to use an amp for my Peche a la Mouche pickup I bring my Supro Black Magick combo amp. At 25 watts it has tons of headroom so I never worry about it distorting. But it weighs almost 40lbs (18 kg) so that's a downside. Great tone but heavy. Hope that helps!

Buco

Yeah, I have Hughes and Kettner 20W combo. Its sound is magic when you get it to the sweet spot but by that time it's way too loud for the gigs I play (I once compared it to my other H&K, 100W head and 20W watts was just as loud to my ears, only 100 watts sound was more "massive" but then the difference between speakers are 12" vs 4X12) And it's also a 40lb amp, not so easy to schlep around. I've been wanting to retrofit to it one of these power soak attenuators for a while now...