So here’s the finished guitar amplifier:

The new Bluetone Crossroad 2+2 amp head is fitted inside its cabinet, and Bluetone’s game-changing wifi-software is up and running smoothly.

Bluetone’s wifi-protocol makes it easy to check and readjust the tube bias on your amplifier’s power tubes. No engineering degree or special tools needed – you only have to have a mobile device or computer to hand.

The amp head is accessed as a web-address. The correct bias values for the power amp valves fitting your amp are listed in the owner’s manual. All you have to do is to type the new bias values into the correct fields, and save them by pressing the ”Change Bias” buttons.

This is what the finished half-stack looks like. It has already been taken home by its lucky owner.

Contact: Bluetone

The time-consuming process of hand-wiring, assembling and soldering the innards of the new Bluetone Crossroad amp head was practically finished by the start of last week. The only thing still missing was the software to run the wifi power valve biasing (the traditional, hardwired bias adjustment already worked, of course).

This is the way a custom-made guitar amplifier should look on the inside – exemplary workmanship and top grade components.

There was still a tiny bit of adjustment work to be done on the metal chassis to make it fit properly into its cabinet.

When all is finished the control panel should be flush with the cloth grille.

From a tonal perspective the Crossroad-head was all dialled-in, thoroughly checked and rearing to go. Matti and Harry gave me a run-through of the sounds offered by this amp’s three channels, and I must say it sounded fantastic!

Only a few hours after my visit to Bluetone’s HQ, I got a message from Harry that the wifi-application had arrived for inclusion in the head.

Valmista tuli!

Uusi Bluetone Crossroad 2+2 -vahvistin on sovitettu koteloonsa, ja firman mullistava wlan-softa pyörii ongelmitta vahvistimessa.

Wifi-ominaisuus mahdollistaa pääteputkien biasointia kätevästi ilman insinööritaitoa tai erikoistyökaluja suoraan mobiililaitteen tai tietokoneen nettiselaimelta.

Putkityypille sopivat biasointiarvot löytyy vahvistimen käyttöohjeesta, ja niitä voi muuttaa tallentamalla uudet arvot kummallekin pääteputkiparille nettiselaimen kautta.

Nyt Bluetone Crossroad -puolistäkki on valmis luovutettavaksi asiakkaalle.

Lisätiedot: Bluetone

Aikaavievän ja tarkkuutta vaativan kokoamisvaiheen jälken uusi Bluetone Crossroad -nuppi on viitä vaille valmis. Ainoastaan wifi-biasoinnin softa puuttuu vielä (perinteinen biasointi johdoilla toimii toki tästä huolimatta).

Tällaisia custom-vahvistimien sisälmykset voivat näyttää parhaimmillaan – erittäin siistiä työtä ja laadukkaita komponentteja.

Nupin kotelo kaipaa vielä pientä hienosäätöä, koska se oli koesovituksessa hiuksen verran liian tiukka, eikä etupaneeli mahtunut sulavasti kokonaan aukosta läpi.

Tarkoitus on, että valmiissa vahvistimessa etupaneeli on samassa linjassa nupin etukankaan kanssa.

Uuden Crossroad-nupin elektroniikka on jo hienosäädetty, ja myös sen koesoitto on viety onnistuneesti läpi. Matti ja Harry esittivät minulle puolistäkin soundeja, ja erittäin hyvältä se kuulosti!

Sain juuri Bluetonelta viestin, että wlan-softa toimii nyt ja on valmis asennettavaksi – Crossroad-projekti lähestyy siis maaliviivaa.

A versatile tube amp, such as Bluetone’s Crossroad, is quite an involved design containing many different components. The exact component layout requires a good deal of planning.

As you can see in the picture above, Matti Vauhkonen has sketched the outlines of all the necessary parts going into the Crossroad onto the chassis’ protective foil. Next he has drilled the holes needed to mount the valve sockets, the circuit boards, the transformers, and the leads going through the chassis.

Designing a tube amp is all about balancing the different requirements of the different parts working inside the amp – you can’t simply throw the components together haphazardly.

The large power transformer mustn’t radiate electromagnetic hum into the audio signal, which is why it is always placed as far as possible from the preamp valves. The power amp tubes, for their part, are best kept some distance from the audio transformer, to avoid hum and buzz induction. The audio transformer also has to be angled correctly in relation to the power transformer to keep things as quiet as possible.

One special feature of Bluetone-amps is their use of (doughnut-shaped) toroidal transformers as power transformers, which is still quite rare in guitar amplifiers.

This is despite the advantages a toroidal transformer offers in comparison to a traditional laminated core transformer. A toroidal transformer weighs less than a similarly spec’ed traditional design, and it also radiates less electromagnetic hum, which makes it easier to find a good spot for the power transformer in the amp.

Bluetone’s Harry Kneckt puts it like this: ”If the toroidal transformer had been available to Leo Fender back in the 1950s, he would have used it in all his amps. I’m pretty sure of this!”

Matti Vauhkonen has first installed the transformers, tube sockets (the white components), and the output jacks (the black parts on the right) into the amp chassis.

The eyelet-boards and PCBs were added for these pictures only to give an idea of their placement inside the Crossroad head. The audio signal in all Bluetone amps runs through a pure, point-to-point soldered analogue-and-valve path, but for modern control features, such as channel switching via MIDI or tube biasing via WiFi, the company naturally uses modern technology.

The next step is the installation of all the front panel parts, such as the control pots, switches, and the pilot light.

Bluetone makes some of their cabinets in-house, depending on their current workload. For the head featured here, Bluetone ordered the arctic birch ply amp cabinet from their subcontractor.

At this moment Matti Vauhkonen is dealing with the time-consuming business of soldering and assembling the heart of the amp (here’s a picture of another Bluetone-model). Hand-soldering a point-to-point valve amp is something you shouldn’t do in a rush, if you want to avoid very time-consuming troubleshooting.