Does the number of tubes on a tube amp affect it's quality?

Leaving aside discussions involving hybrid tube amps, does the number of tubes on a tube amp affect quality?

Seeing as we have Tube amps with anywhere from 2-10 tubes on them, I was just wondering if there was a rational for why it there needed to be more than 2 tubes.

 

different tubes for diferent usage i think, like rectifier tubes, driver tubes, power tubes, et al. but soundwise, it depends on the quality of parts and the design, not necessarily on number of tubes alone.

 

Being totally unqualified to answer this question, I consider it my duty to put in my sixpence.

Does the number of tubes on a tube amp affect quality?

Yes, but not always for the better. The number of tubes constitutes only one small variable in the multitude of factors that influence sound quality.

Why do there need to be more than two tubes?

Tubes have all sorts of functions. The number of tubes used is partly determined by whether a function is needed in a particular design and partly by whether the function is fulfilled by a tube or some other component/s. Here are some examples of some tube functions:

1. To amplify voltage
2. To amplify current
3. To rectify incoming AC power
4. To regulate voltage
5. To drive another stage
6. To lower output impedance
7. To set the bias of another tube
8. To function as a constant current source
9. To make an amp look pretty
10. To sell amps to people who think just having a tube somewhere makes an amp sound better

 

More tubes certainly affects the sound. However you need to know that there is many different types of tubes. Some tubes have dual triode or pentode sections. This means that what could normally be done with two tubes can be done with one tube with multiple sections.

Other then that the main reason to use several identical tubes is power output. An amp with multiple tubes is likely to sound different because you are finally getting enough power to drive your speakers properly where another design runs out of gas. With several tubes the need for tube matching might not be as important because the different characteristics average out.

But a lot of it is design dependent. Take for example a single ended kt88 amp. Even if you have 2 kt88 tubes in parallel you are likely to have a similar sound to just one kt88. This will sound totally different to a push-pull amp using two kt88 tubes.

 

Two?



Yeah, yeah, it's a hybrid, but still.. Dual triode! Kick-ass little amp, too.

Levity aside, I think the answer to your question is somewhere between "it depends" and "how long is a piece of string?". There are many topologies, many designs, hell, many choices of tube- simply too many variables to say "X tubes will sound better than Y". You're probably better looking for specific impressions of the amp(s) that you're interested in, to get an idea of what they're like.

 

As a relative newcomer whose been doing a lot of research into tube amps, it looks like — overall — there's a balance. Ignoring hybrid amps like the above, which can sound great but do a lot of their work with solid state electronics, it seems like the amps that consistently get great reviews have just as many tubes as they need to get the job done and no more.

From an engineering perspective, this makes sense. Designing a circuit to achieve a given task while trying to minimize the number of tubes (and not falling back on more modern components which serve similar purposes) will compromise the design. This may manifest in an amp that just doesn't have the power needed for certain drivers (whether that be headphones or speakers) or it may compromise audio quality in other more (or sometimes less) subtle ways.

However, the more tubes you add to a stage or stages you have in an amp, the more opportunities there are to degrade, distort, or otherwise alter your input signal (beyond pure current or voltage amplification). To some extent this is desired in a tube amp, since I think most would agree if you want the most transparent amp possible modern solid state designs are the best choice. However, if you start adding tubes (or really any other component) in an effort to make an amp look cool, then again you're likely to compromise audio quality along the way.

In short, I agree with the above comments. Choose an amp based on suitability to your needs, reviews, and overall sound. I think it's fair to go looking for a tube amp for aesthetic reasons, with the understanding that you may end up paying more to achieve the sound profile / quality you're looking for, but I wouldn't worry too much about the number of tubes alone.

 

@Chaos215bar2

http://www.superbestaudiofriends.org/index.php?threads/new-members-introduce-yourself.17/

 

The best tube amps KISS with 2-stage or even 1 stage design. A lot of the stuff that has a lot of glowy stuff for the purpose of having glowy stuff does not sound good IME. There's a reason you see people sticking to more or less the same formula