Tube Guitar Amps and the Tube Sound

Do Tubes Sound Better Than Transistors ?

The great debate continues.... I guess if you want an original sound from the 60's and 70's then it's difficult to beat a tube guitar amp. New transistor designs are quite clever these days though, but don't get drawn into thinking you've bought a tube amp because it's called something like 'Transtube ®' which is a Peavey product and even has a logo including a picture of a tube. Transtube ® is a semiconductor circuit designed to emulate a tube amp sound.
Then there's modelling amps which synthesise vintage tube sounds. These aren't bad but they can have that harshness associated with digital effects.

Tubes (which in Europe are also called Valves) produce a more mellow, easy listening sound. A sound that isn't so harsh or so tiring on your ears. Not that there aren't some great sounding transistor amps out there of course.

But why do tube amps and transistor amps sound so different?

The main reason for this is in the way the devices work. OK - both tubes and transistors amplify the signal, in this case, your guitar, but as you increase the volume towards the maximum the transistor or tube can handle, the output can't increase any higher and clipping begins to occur, and this is where the subtle sounds of the tube win out.

If you want to see an image of a clipped sign wave you can see it here - don't get over excited though : ) Notice the 'flattening out' at the top and bottom of that wave form.

Now when a transistor clips, it clips very fast creating a very flat, sharp edged clip which in turn produces odd harmonics which are objectionable to our ears. When a tube clips it tends to compress the waveform, which will be even more noticeable if your amp uses a tube rectifier as it will suffer from something called 'sag'. When I say 'suffers' this isn't an unpleasant effect. Tube clipping is more subtle, producing more even harmonics which are more compatible with our ears. An altogether warmer sort of distortion, some call it more musical.

One of the downsides of a tube guitar amp is maintenance. Tubes do wear out with use, they run hot because they have heaters inside them and operate at pretty high voltages - approaching 500 volts or so. They're made from glass and inside the tube is a vacuum. Electrically they're probably more robust than transistors, but they're physically more delicate.

As tubes 'wear out' they lack sparkle and punch and sometimes become noisy. They can become microphonic introducing noises from external vibration and even sound from speakers.

Good quality tubes aren't cheap either, so when it comes around to replacing output tubes which should be replaced with a matched set of 2, 4 or even 6, it can be a 'expensive hobby' as they say in the UK : ) You should also get a techie to check the bias when output tubes are replaced which will not only keep your amp sounding as it should, but maximize tube life.

So is it worth investing in a Tube Guitar Amp? Well depends on your budget I guess, but I think so.