Firefly 1 Watt Tube Guitar Amp Build

[illwood]

Based on the response from massacre's guitar string thread, here is my tube amp build thread. This was my first larger scale electronics venture. I have repaired laptop power jacks in the past, wired my own guitar pickups, and modded a pedal or two, but nothing from the ground up. I see a Marshall 1974X clone in my future. . . If I get good at it, maybe a little bit of a side business.

The amp is a 1 Watt Firefly as designed by Doug Hammond.

First off, the background work. . .

I decided that I wanted to build this on a turret board (old-school) and that I wanted it to be in a form factor that would fit on my 80's Marshall Lead 12 Micro Stack. With that in mind, I proceeded to layout my board (on paper first).



Then I transferred that into a CAD layout for the turret board and finally a solid model of the chassis.







Note that I decided to move the power lamp before construction, I did update my model, but didn't create an image of it.

[illwood]

I printed out the turret board layout full-scale and used it with a center punch to locate the holes.



Here is the board with the turrets installed. The extra holes by some of the turrets are wire routing holes like some Marshall amps of the past.



The completed board loaded with components.



The wires installed.

[illwood]

Some close-up shots of the turret board.

[illwood]

Front and rear views of the drilled chassis (with the power transformer mounted). The chassis is an off-the-shelf Hammond aluminum enclosure.





The underside showing the power wiring and tube sockets installed.



I wrapped the grey (115VAC) tap from the 269EX transformer and then taped it to the chassis to keep it from flopping around.

[illwood]

Here is the turret board installed in the chassis.



This view shows the wired front panel and the tube sockets with the heaters wired.

[illwood]

The completed chassis:



Controls (from left to right):
Power, Standby, Power Lamp, Boost Switch, Boost Knob, Volume Knob, Input Jack



Rear-view controls (left to right):

Impedance (up is 4Ω, down is 8Ω), Speaker Jack 1, Speaker Jack 2, Fuse, Mains Input



Gut shot (a little messier than intended, but not bad).

[massacre]

That
is
one
of
the
coolest
things
EVAR!

I went to a website looking for a kit, but I guess they don't make them anymore?

Have you played it yet?
How does it sound?
I would love to do something like this.
About how long did it take you?

[illwood]

That
is
one
of
the
coolest
things
EVAR!

I went to a website looking for a kit, but I guess they don't make them anymore?

Have you played it yet?
How does it sound?
I would love to do something like this.
About how long did it take you?

Thanks!

Ah, that must be the "Firefly PCB" that a guy was selling for a while. I saw that, but decided to go the turret board route. I think the design files for that are still available and *technically* you could make your own PCB with a laser printer, copper clad board, clothes iron, ferric chloride, and some patience.

I've played it a bit now. Honestly it is too loud through two 10" speakers to get it to distort naturally and not bother the people in my building. It sounds good, I don't feel like it needs any tone controls. I would layout the board a bit differently because I had some problems with some wires getting too close to each other, causing some squealing when you crank the volume.

It probably took about 20 hours to build. I didn't keep track, but that seems like a reasonable estimate. Things would have gone faster if I had access to a full-size drill press and some Greenlee punches.

I bought all of the parts Mouser Electronics and The Tube Depot. The turret board is a pretty easy way to make the components easy to swap out. If I were to build it again, I would consider a bit larger of an enclosure or etching a PCB for it if I wanted it small.

Fortunately, all of my future plans are for bigger amps that will have more working space inside the chassis.

Lastly, I do intend to build a wooden enclosure for it, but I haven't started that yet.

[massacre]

That is great. So cool. Did you use 6L6 tubes? I see they are Fender, wondered if you had considered any of the Russian brands.
How many are power tubes?

I like the turret board setup, and all of your wiring looks awesome, as well.
Any reason for the 2 10" speakers?
I have always liked 12" speakers for guitars.

[ImpalaSlayer]

cool as ****, i dont know what it does but cool to how its built

[fastblackmerc]

cool as ****, i dont know what it does but cool to how its built

+1!!!!!!!!!!!!!

[Mote]

Does this use a 12ax7 for the power tube? Arfe the 3 tubes preamp, phase inverter, power?

Nice work! Looks plenty clean. Now you have to learn coverings, grill and piping :-)

[illwood]

That is great. So cool. Did you use 6L6 tubes? I see they are Fender, wondered if you had considered any of the Russian brands.
How many are power tubes?

I like the turret board setup, and all of your wiring looks awesome, as well.
Any reason for the 2 10" speakers?
I have always liked 12" speakers for guitars.

Does this use a 12ax7 for the power tube? Are the 3 tubes preamp, phase inverter, power?

Nice work! Looks plenty clean. Now you have to learn coverings, grill and piping :-)

Actually, it preamp tubes for everything. A 12AU7 is used as the power amp tube (though it acts like 2 tubes because it has a separate anode, cathode, and grid like the other two preamp tubes). A 12AX7 is used for the boost circuit and another 12AX7 is the main amplifier. The boost tube is bypassed when it is off. There isn't a phase inverter, so this is a Class A amplifier. For tube brands, the Fender / Groove Tubes labeled ones are the 12AX7s and they are Sovteks (I bought them cheap from a guy who was trying some different tubes in his Fender combo). The 12AU7 is an Electro-Harmonix, so technically, they are all Russian tubes.

As for the speakers, I am also typically a 12" speaker guy, but I picked up an 80's Marshall Lead 12 mini stack that has two speaker cabs with a 10" in each (that I upgraded to Celestion V10-60s). I thought that a 1 Watt tube head would be a nice option for it.

As for the enclosure and covering, I'm not concerned with picking it up. I have built and covered several custom sub boxes that I built a few years ago and I'm a quick learner.

[Motorhead350]

When you finish play on it and record it. I wanna hear that sucker. Might even buy one from you if you decide to sell.

[musclemerc]

Illwood, post up some pics when your done. I grew up working on 2 channel tube amps. LOVE the sound, true audiofile quality.