Very Clean Tube Amplifier Design Project

Karel-Mars · 2011-03-04T13:45:51+00:00

I was asked to design a 30watter that is very, very clean and easy to DIY. My head immediately thought Fender AB763 circuit with 6L6GC's. To keep it simple...

Very Clean Tube Amplifier Design Project

guidothepimmp

they dont come cleaner than my elk.

twas ok when i got.

twas freakin awesome when jp finished with it..

love the pics K.

keep us updated

Tonedef

I think there might even be people who would be interested in this sort of design, if they are happy with their faux amp modelling.

(I'm probably one of them ?)

Gearhead

My amp has this ultralinear switching as well and I must say it cleans the sound up, to the point that I mainly play acoustic or chorused sounds through it. For fat rhythm and even for clean rhythm I rather opt for penthode mode. In any case, a recommended feature to have if you want clean tone!

Karel-Mars

Thanks for the enthusiasm ?

I'll keep you posted. The idea for the UL switch is for acoustic playing. Pentode mode should deliver classic deluxe/princeton sound.

Karel-Mars

After three days of rolling the power transformer I tested it yesterday. No short circuit and voltages are within spec, but slightly on the high side.

With 225VAC going in at the mains side I get

470V DC with a current draw of 70mA
6.7VAC on the filament tap

I am happy with the outcome; under full load the levels should drop a 10%.

Now for the turret board...

makepeace

Coool project. Very interested in how this turns out.

Karel-Mars

Here's a preview of the turret board - you have to guess the values of the components ?

The Negative Feedback loop stays disconnected for now, but the resistors are in place. Volume/Treble/Bass not drawn in. Brown things are resistors and Yellow things are coupling caps. Light Blue things are electrolytic caps.

Karel-Mars

I have made a drawing of the layout on the turret board:

aja

Karel wrote: I have made a drawing of the layout on the turret board:

Where do you buy such a long napkin with grid lines printed on it? ? ?

Karel-Mars

@Aja: they should bring out grid printed napkins for amp builders :?

Here's some pics of the turret board manufacture.

I have decided to put the first filter caps off board, due to their size.

GuitarGeek

So, the kit has arrived from Karel and work is about to commence. Now to clean up that workshop... yikes! what a mess, might take me weeks to clear some space... Anyway, when that is done, we'll start with wiring up the turret board. Watch this space for photos.

GuitarGeek

Right, ready to go, just waiting for final circuit diagram and components. Any idea when I'll get these, Karel?

Demigod

You know, if you want VERY clean, i would suggest solid state. Just saying. "Distortion" was originally a side affect of having tubes...

Gearhead

Very clean also means no transient intermodulation distortion and no higher order harmonics, so you want to steer clear of the solid state stuff imho... 8)

Demigod

What you say is very true, but once you have a circuit that cancels those effects, it is cleaner.

ezietsman

Demigod wrote: What you say is very true, but once you have a circuit that cancels those effects, it is cleaner.

I think what Gearhead is trying to say is that the amp is very clean for a guitar amp. In the engineering sense of 'clean' its probably rubbish. Its very easy to make an amp without audible distortion but they are very stiff on the attack and sound sterile. The whole point of a valve amp is that they're not clean, even tho we refer to 'clean' sounds as being without distortion, they prob have total harmonic distortion levels orders of magnitude higher than the average hifi amplifier. Its what makes them sound 'warm'.

Demigod

Oh ok sorry bit of a misunderstanding here lol. Sorry XD ?

Karel-Mars

To add to the discussion:

When someone asks for clean, I hear them asking for the sound of an acoustic guitar. So the electric sound has to be coloured to become more woody. That is something that tubes do naturally.

OK dudes and dudesses, here's the layout of the turret board with component values added. The tricky configuration around the 6L6GC cathodes are called the Blumlein Garter circuit. It balances two unbalanced tubes perfectly.

I have noted some errata: the second triode of tube 1 does not have a cathode resistor mounting space. Maybe the two triodes should share the same resistor?

The cap that couples the preamp to the phase splitter is also not defined. It should be 0.001 or has to be tweaked for optimal sound.

bottledtone

If experimented with sharing of the cathode resistor and it worked up to a point and then did some serious motorboating! Rather use a small tag strip and connect it to the 3mm bolt on the preamp shield/socket and then the resistor straight from the pin.

GuitarGeek

@Karel

... here's the layout of the turret board with component values added. The tricky configuration around the 6L6GC cathodes are called the Blumlein Garter circuit. It balances two unbalanced tubes perfectly.

and

I have noted some errata: the second triode of tube 1 does not have a cathode resistor mounting space. Maybe the two triodes should share the same resistor?

The cap that couples the preamp to the phase splitter is also not defined. It should be 0.001 or has to be tweaked for optimal sound.

Hi Karel. Is the circuit in your latest post the final turret board design? I want to start building, and would prefer not to have to go back and make changes afterwards.

Any idea when I'll be getting the outstanding components?