Never Owned a Tube Amp and Want Advice


Hi All, 

I have never owned a tube amplifier before and am planning to purchase one with a minimum of 50 watts per channel to mate with 8 ohm 88 dbl speakers.

My hope is experienced audiogoners will share their expertise regarding how to approach this. While I realize listening is the best way to learn about sound and compatibility; I want to learn a better understanding about brands with less maintenance and longer tube life, how to decide between mono or stereo,can a newbie play with bias or is auto biasing a better first choice, etc.

I would also appreciate what to look for in selecting a used tube amp to identify one that might be in need of repair. For example, with solid state depending on the brand, capacitor replacement can be more of a concern. Any advice on what to look out for or ask about with used tube amps would be appreciated.

A big question I have is how to understand the relationship between power tubes like E34's, 120.s, etc. and, I guess the driver? tubes like 12au7's and 12at7's. That  is to ask which is more critical to the overall sound of the amp? FWIW, I routinely tube roll with my preamps.  

I 've read through a number of threads but maybe someone can point me to good ones I may have missed. 

Thanks for listening,

Dsper
dsper
Now 'peak power supply' as you put it might be a current rating that has to do with what happens when you short out the power supply, and might be stated in amps. This is really a statement of how much energy is stored in the supply (and how big the spark will be when you short it out) rather than anything to do with how much power the amp makes.
To be perfectly clear, energy stored in the supply is how an amp can handle an orchestral crescendo that would cause it to exceed its continuous power rating, correct?


Since this is a conversation about having enough power, what about going for a larger tube amp  like 100 wpc.

This assumes that the 60 wpc amp builder can build an equal quality 100 wpc amp.

While it might be waste of money, I would never have to worry, correct?




There are trade-offs, aside from cost, with going for more power.  With some brands of amps, the cheaper, lower-powered version sounds better when playing at modest volume level than the higher cost, higher priced brethren.  This can be the case with solid state too.  I tend to find higher powered tube amps to sound a little bit brittle and hard (harsh?) sounding.  But, it is still far better to get an amp compatible with your power requirements and accept the less significant trade-offs.

You need to hear these things for yourself.  It is hard to say what you will like and dislike and how you would value the particular attributes of any given amp type, never mind particular model.  If you can, listen to a modestly powered EL34 or EL84 amp (a popular tube in lower cost amps that sounds very good), a higher powered amp using KT 88 or KT120 or KT150 tubes, and an output transformerless amp, like the Atmasphere S-30 or M 60 amps.  Of the more common tube types, I am a big fan of the 6L6 tube, but, those put out less power than the other tube types I've mentioned.
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To be perfectly clear, energy stored in the supply is how an amp can handle an orchestral crescendo that would cause it to exceed its continuous power rating, correct?
No. The extra energy is useful to reduce IMD at higher power levels. Essentially it allows the power supply to have less noise- and less noise in the power supply results in the lower IMD of the amp.
Since this is a conversation about having enough power, what about going for a larger tube amp like 100 wpc.
As you increase the power of most tube amps, the output transformer has to be able to handle that power and at the same time make bandwidth. The problem is this basically doesn't happen; with output transformers as you build progressively larger devices, bandwidth is increasingly more difficult to obtain. For decades, 60 watts was the 'sweet spot' for push-pull tube amps, where they could make the power and still have the bandwidth needed (5-100KHz). You may not think that bandwidth above 20KHz is important, but unless you have a great degree of feedback (above 35dB or so) that bandwidth is important to prevent phase shift which can cause issues with tonality and the soundstage presentation.


Another thing to think about is the simple fact that 100 watts is not a great deal of power over 60 watts insofar as the ear is concerned- its slightly less than 3dB which is barely louder to the ear. But a 100 watt amp might have other properties (assuming bandwidth isn't an issue) at lower power levels that could be in its favor. So its a mixed bag.

OTLs get around the bandwidth issue by getting rid of the output transformer, so that tradeoff does not exist in them when going to higher power levels- a 200 watt OTL can be as fast, dynamic and transparent as a smaller one.