[Merck]

I have noticed that many people love tube amplifiers and other tube related equipment and I had some questions.  What are the things you look at first when it comes to choosing a tube amplifier?  What is it you prefer about tube amplifiers over other types?  I think they are beautiful to look at though I have never had the opportunity to listen to one considering the lack of high end retailers in my area.  Other than the sound, what is the next most important element of a tube amp in your opinion?

 

[Uncle Erik]

Build quality is huge.

I only buy tube gear with name-brand power transformers. Good ones run around $75 and up. You do not want to trust high voltage to something cheap. If you're buying a $200 amp, ask yourself how much of that goes into quality parts.

Likewise, good ones should be built point-to-point. I don't like high voltage and high heat on PCBs; they're better suited for solid state. A PCB can hold up, but they're difficult to repair if they get damaged.

Continuing on with the power transformer, the power supply should be of high quality. You do not want four diodes and a couple of cheap capacitors doing the rectification. A tube rectifier is better, you want big capacitors and, preferably, a few chokes to really smooth the power. I prefer to have tube filaments run on DC instead of AC. AC costs less to manufacture, but it's harder on the tubes and sounds less precise.

Also, I like output transformers. They get the output impedance much lower which is a big help in increasing the damping factor.

You'll find these things on better tube amps. The reason cheap tube amps lack these things is because they cost money.

A gigantic myth is that cheap tube amps are cheap because of lower labor costs.

Bullpoop.

Cheap tube amps would cost about the same as expensive ones if they had these things. Cheap amps are cheap because they cut all - and I mean all - the corners.

The only way to cheap out without compromise is DIY. Even then, you'll put $400-$500 of parts into the amp. That's raw costs, not including labor.

The good news is that a tube amp done right will last a lifetime. You'll need to change tubes and drop in fresh electrolytic caps every so often, but that's like changing the belts on your car. You have to do it now and then.

 

[Merck]

Thanks for the response.  I really like the look of tube amps and when I get to go to a meet or perhaps an electronics show I'll be sure to try some out.  I think its pretty interesting that one can change to different tubes for a different sound.  Are these amps primarily for high impedance cans or are there models that can work with more efficient ones or perhaps both?

 

[Uncle Erik]

Honestly, I think the look of a tube amp is responsible for many sales. If you go back to the Golden Age of tubes you'll notice that tubes were always placed inside the chassis. Modern tube gear always puts tubes on the outside because people like to see the tubes.

Not unlike early electric light fixtures. The lightbulb was a huge novelty when introduced, so most fixtures didn't have shades because people wanted to see lightbulbs and that's what sold. As lightbulbs became common, glass and other shades were used.

Do not get hung up on tuberolling. Tubes only contribute a little bit to the sound and I don't want to amass several hundred dollars of tubes so I can plug and unplug them looking for differences. I think it's better to use a good set of tubes and listen until they die. Besides, the circuit used is more important to the sound, as well as the power supply and output transformers. Putting $200 tubes into a cheap amp that lets AC ripple into the main (B+) power is probably not going to sound as good as a well-filtered amp with $20 tubes.

The problem is that most people don't bother to learn what's going on inside. All they do is read a review fromsomeone sayin that it sounds good (you can find a positive review of anything, by the way) and an attractive case.

Also, do not assume all tube amps sound the same. There's a lot of variation. Hearing one does not give you an idea of what a wider sample sounds like. Here's a small list of what makes a difference:

1. Diode or tube rectification
2. The use of chokes and power supply filtering
3. Whether the power supply is regulated
4. AC or DC on the filaments (you can regulate the filaments, too)
5. Amplifier class (usually class A or AB)
6. Circuit topology (single-ended or push-pull are common, but there are more)
7. OTL or transformer-coupled output (output transformer quality is critical)
8. Types of tubes used (directly-heated triodes (DHT) sound different)
9. There's another layer of complexity in designing the circuit and determing how the tubes are run and how the signal is routed

All of these are much, much more important than the tubes you run. Using some rare NOS tubes and putting Black Gate capacitors inside is no guarantee of quality. It's like putting 20" rims and a wing on a crappy economy car. A true sports car with ordinary steel wheels and no wing will actually give you performance.

 

[wuwhere]

They get hot too, the output tubes, I have two all tube amps, one 10wpc and another 60wpc

 

[Merck]

Wow I appreciate you taking the time to provide so much detail.  I think I will busy myself with some reading before actually making a purchase, and now seems to be a good time to do so since I can afford a book but not an amp or a set of headphones that would require one.  I know what you mean about the older tube equipment not having tubes on the outside.  The only tube device I have ever used was a HF transceiver and it was this way.  I remember being able to remove the back of it and seeing all the internals.  Very cool stuff.  Radio is a hobby I should attempt to revive.  Unfortunately I let my license expire.

 

[wuwhere]

If you're getting into tubes, get or make one that uses readily available tubes. NOS tubes are expensive. New tubes are mostly made in Russia or China. Most tube amps require matched output tubes. Some have auto-bias circuit. Others have manual bias. My 10wpc amp has auto-bias but my ARC amp has manual bias for each output tube. I use a true RMS multimeter to bias each output tube.

 

[Merck]

Quote:

If you're getting into tubes, get or make one that uses readily available tubes. NOS tubes are expensive. New tubes are mostly made in Russia or China. Most tube amps require matched output tubes. Some have auto-bias circuit. Others have manual bias. My 10wpc amp has auto-bias but my ARC amp has manual bias for each output tube. I use a true RMS multimeter to bias each output tube.

I do plan on at least venturing into the tube amp side of things.  I was most interested when I learned about DIY kits for beginners like the Bottlehead Crack.  I know which end of a soldering tool is hot so I thought it might be fun to put something together myself.  Cost is the only thing holding me back at the moment, I just have too many other priorities and not enough income.  Once that changes I'll give it a try but until then I'll do some reading about electronics and audio.  

 

[wuwhere]

Get a good soldering station with variable temp and changeable tip. I have a Hako 936 with a Hako 907 soldering iron. I use a Fluke 89 multimeter but I think the 87 is good enough. Get some good grabber clips also. And a solder sucker.

 

[Merck]

Would the solder chose be extremely important?  I hear people talk about silver and what not.

 

[wuwhere]

Quote:

Would the solder chose be extremely important?  I hear people talk about silver and what not.

No. I use Radio Shack 62/36/2. Circuit boards populated with parts go through a solder wave machine and the solder used is as inexpensive as possible. So why should I use expensive solder?