Stickman builds his first tube amp

Stickman393

Stickman393

Well-known member
I love high voltages.

I eat 480vac for breakfast.

I, also, constantly yern for death.

So, why not attempt to hasten that by diving headfirst into high DC voltages and learning as I go? Ya know...it just seems right. It's time. My first tube amp build. Fuck yeah. Let's tempt fate. Todestrieb jetzt! Zum Teufel!

So, I'm starting off simple enough. 5F1. The classic fender champ. But I don't want to build a boring fucking champ. I want my champ to look at other champs and say: fuck you, man. You're living in the past. I can crank slightly louder, have a little bit more low end, and stole your wife.

Which means I'm looking for a slight challenge, rather than going straight to a kit. I actually want to learn about what I'm doing here, and getting all the pieces hand delivered to me might be cheaper and easier...I insist on doing things the hard way.

So. First off. The pre-bought pieces:

- I don't want to have to dick around with winding my own output transformers just yet. So the OT will be sourced from amplified parts, as their standard "champ" OT. It's multi-tap, so this will allow me to add an extension cab output for a 10-12" speaker should I choose to add one.

- I'm not building a goddamned speaker. So, I'm slapping in a Weber 8A125 @ 20 watts. 1.25" voice coil 8" alnico speaker. Slightly more modern, still room for cone breakup. Just a subtle tweak to the formula. Because I want to.

- Chassis: as much as I want to take on a shop press project where I weld structural steel bars into a frame that can handle a 20 ton bottle jack and a sheet metal brake attachment, I haven't learned how to use my stick welder yet. This is a "in the future" thing. So I bought a cheap $60 chassis off of AliExpress that I'll need to modify a touch. It's thick as balls and can be used as a deadly weapon.

- Power Transformer: way over my head to wind. Unfortunately, these are some of the most expensive components for the amp build. Standard laminated plate transformers are...like...easily over 100 bucks. I am, famously, a cheap bastard who likes to make his own life hard...so instead I sourced an Antek AS-05TC250 toroidal transformer. $38. The higher voltage taps on this guy are only 250vac, as opposed to the near 300vac I see on some of the "vintage" models. This should be fine. Actually, better, considering other parts of this build.

Tubes: I like JJs. Partially because of the aforementioned cheap bastardry. 6L6, 5Y3, ECC83.

MODS!

Rectum-frier switch: gonna do a DPDT that switches an additional resistor in series with the cathode bias resistor while swapping out the 5Y3 for a solid state rectifier. Why not.

Negative feedback mod: planning on adding this little potentiometer in there, cause it's easy and looks like fun.

Soft-start: gonna wire a NTC thermistor in series with the primary windings of the toroid. Toroids are motherfuckers when it comes to inrush current; a well-chosen NTC thermistor in series will smooth that out while presenting a negligable load in series with the transformer when warmed up.

The cabinet:

Well...huh. How much do those cost? Fuck that. Nah dude.

Ive got a better idea: I've got some Jatoba (brazillian cherry) laying around. 4/4, S4S, heavy, dense, hard, and brutal on cutting edges. Why dont I just build my own cabinet from what I have on hand?

Easy enough. Router table, finger jointing jig. Give it a nice finish. Jatoba in particular is great for this application because of how much of a motherfucker it is. It sinks in water. It does not float. Internal resonance, you ask? Fuck off, built right this stuff is basically pretty HDF. So long as the grain orientation is correct, I brace in the inside, and I use a floating baffle I shouldn't have an issue with seasonal expansion.

The circuit board:

Gonna carve one up on my CNC and turret it. Probably with some reference to how we should sieze the means of production hidden in there.

Come with me folks. Hold my hand while I poke around in this thing while it's live.
 
Seen that site, glanced over it, looks interesting. Was planning on taking a deeper look along the process here.

What I've learned so far: not much.

Getting the toroid to fit will be interesting. I'm gonna have to have it hang over the side a little, but there's gonna be lots of open space on the side of the amp.

I'd eventually like to be able to make a few more over time...a 5E3, an 18watt marshall. Some kind of high gain, low watt monster. Something for my bass.

But the thing is...transformers and tubes are a son of a bitch. This ain't building pedals: the base costs for components are so much higher.
 
Rob Robinette’s EF80 (edit: not ef90) 2W output with little pentodes have had good reviews. Is it going to flap your stick shorts in the breeze like a 30-50W PP EL34? Nope. Will it sound really good and have cheaper output transformers? Yep. And yes, transformers
are ri-goddamn-diculously expensive.

The SMPS are getting good reviews from people to power the preamp (and smaller power amps). Only would need a 12-24V DC power supply.
 
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Stickman393 said:
Seen that site, glanced over it, looks interesting. Was planning on taking a deeper look along the process here.

What I've learned so far: not much.

Getting the toroid to fit will be interesting. I'm gonna have to have it hang over the side a little, but there's gonna be lots of open space on the side of the amp.

I'd eventually like to be able to make a few more over time...a 5E3, an 18watt marshall. Some kind of high gain, low watt monster. Something for my bass.

But the thing is...transformers and tubes are a son of a bitch. This ain't building pedals: the base costs for components are so much higher.
Click to expand...

"But the thing is...transformers and tubes are a son of a bitch. This ain't building pedals: the base costs for components are so much higher."

Right there! that was going to be my next question "how much are you into it already?" and that's the reason I have not bit the bullet yet. I was going to get a Boot hill kit, he seems to use good components Link to his kits <- that's the one Ive been eyeballing. I feel a kit for the first one for me would be key... then there's cab or cab and speaker if doing a combo. I see your going to make your own! gonna be a combo? I also want to do a 18 Watt Marshall. looking forward to see your process.
 
pbrommer said:
Rob Robinette’s EF90 2W output with little pentodes have had good reviews. Is it going to flap your stick shorts in the breeze like a 30-50W PP EL34? Nope. Will it sound really good and have cheaper output transformers? Yep. And yes, transformers
are ri-goddamn-diculously expensive.

The SMPS are getting good reviews from people to power the preamp (and smaller power amps). Only would need a 12-24V DC power supply.
Click to expand...
I'm not seeing the EF90 2w, can you shoot me a link? that's exactly what i'm looking for, good sound, cheap, simple, can sound good at lower volumes late at night.
 
I've built some killer cabs with laminated purple heart, walnut, and maple but at the end of the day thru an 8/10/12" speaker I just never got a Champ to sound good. The buyers sound superb thru them and I've done all the neg feedback and such mods but I've just never got them to sound good. I think that's true of all Fender amps because I can't play a Deluxe or Twin either. Nor a Big Muff. I'm cursed.
 
Gonna be a 1x8 combo. Small, portable, good for plugging in with a pedal or two is the idea. Just for a change of pace from my massive FM9 pedalboard & 1500 watt SS poweramp.

Going with a toroid transformer has several advantages, not the least of which is the fact that they're significantly cheaper than the new reproductions.


www.antekinc.com

AS-05TC250 - 50VA 250Vx2 Transformer

Toroidal transformers and power supplies
www.antekinc.com www.antekinc.com

Power transformer: 50 va, two 250v secondaries, a 6.3v secondary, and a second 6.3v secondary with a tap for 5v.

32 bucks from antek. Alternative EI transformers run between 1.6-4x the cost. 50Va for a 5 watt output.


22 bucks. Output transformer for the champ. Does the trick, cheap.

Chassis:

Sourced from AliExpress. Like...60ish. welded, heavy duty, looks clean.

Tubes:

I've got plenty of ECC83S laying around. Did a double mica 6v6 and a 5Y3. Maybe 50 bucks.

speaker:


$108. I'm going for a slight modern/vintage vibe with this build, with a little extra clean headroom and a little tighter low end. The toroid is gonna make the amp feel a little less saggy, and having the ability to switch to diode rectification will add to that. The speaker ain't vintage correct as it has a slightly larger voice coil. At this point it's more like cooking than science, I'm just adding a dash of this and that to fulfill my aims on the build while keeping the character distinctly "champ".

The cabinet will be finger-jointed Jatoba. Pretty common for high end speaker enclosures as far as I can tell. I picked up a bunch a while back when I lived next door to a hardwood lumber yard. To say it's harder than maple is akin to saying that fish prefer wet enviornments.
 
Cool project, even cooler presentation ;) I'll gladly follow this one!

One comment though, if I understood your DPDT idea: I would advise you to do this one as two separate switches.

- One for the cathode resistor, and in parallel instead of series. Should have less pop, and then you can use it while playing. Could even have a pot there to fine tune the value.

- The rectifier one if I understand correctly will be only for when the amp is off. So there is that - but you might want to check the voltage rating of the switch. Often 250V is pushing it.

And yep, pretty expensive but (imo) so much more fullfilling than pedal building when (if) it works. A good trick is to salvage transformers from other equipment. A lot of combos are sold 'dead' and very cheap and you can harvest one or two transformers, a speaker... and then you have a small stock and can iterate a design easily.
 
Can't say I'm following your train of thought when it comes to splitting the rectifier switch. Maybe I should explain why I'm inclined to do it as an DPDT:

Switching under load would be a bad idea: it would result in an instantaneous ~100vdc jump and a corresponding surge in current. I might look into engineering a work around for this, but my initial intention here is to only ever use the rectifier switch while the amp is off. Too much stress to the caps, tubes, and transformers otherwise.

That surge in voltage is why I would switch the cathode resistor at the same time; my 250v secondary is a bit lower than vintage spec, so I plan to compensate by reducing the resistance of the cathode resistor while in tube rectification mode. With solid state rectification, it's gonna operate right about where it does in vintage-spec, but I'll be running that 6v6 *super* hot if that resistor's value isn't increased. Taking care of both simultaneously makes the most sense to me...just to avoid cooking a 25 dollar tube prematurely if I forget to hit the second one.

Even considering doing something with an on/off/on DPDT, where the "off" position would essentially leave the 250v secondary interrupted like a standby switch. Though...now that I'm thinking about it...it would be far safer to do both legs of the 250v secondary rather than just one leg. So...3pdt. Dammit.

Gotta...fester...on this a bit.
 
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I understood it so that the cathode resistor change would be more of a voicing option, not to compensate the operating point from the rectifier voltage change, and I was thinking about the preamp. So your reasoning makes sense :) Not even sure how they do it on an actual rectifier...
 
That's more like it. That's pretty clean as a way to incorporate a standby with a switchable rectification circuit. I'm loathe to add two switches, though. Might have to get creative on the backside of the amp.

Hadn't thought of going between cathode and fixed bias, either. Probably won't incorporate that: there's only so much room in the chassis. Mayyyybeee. I'll try to leave some space in case I change my mind in the future.
 
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