Why the high price for tube amps?

Transformers are frequency limiting devices. You can design them for wide response, but it will cost you. For instance, a 400Hz transformer will be fine for voice (there was a time when there was plenty of 400Hz transformers from airplane use so people would use them to build modulators for AM transmitters), but woudlnt' do well reproducing lower freuqencies. A 60Hz transformer would reproduce those lower frequencies, but might not do so well at higher frequencies.

So unless you start with a decent amplifier, you may find the transformers limiting. Tube audio amplifiers were the norm for decades, there is nothing magical about them. They can be cheap and used for PA use, or they can be expensive and used for extreme HiFi, or somewhere in between.

If they are cheap they will be a limiting factor. If they arent' cheap, then there wont' be a lot in the amplifier that is limiting.

You can always use bigger coupling capacitors and bypass capacitors, improve the power supply filters, but if the coupling transformers are inferior, the amp will be inferior.

One difference between solid state and tube amplifiers is that the transformers are eliminated. Different topology brought about by solid state being low impedance while tubes are high impedance. You actually see that, early audio amplifiers were designed like tube amplifiers, complete with output transformers, maybe even coupling transformers between stages. But soon the shift was done, the full value of the transistors put into use, and the transformers gone. Which mean amplifiers that were lot flatter than a lot of the previous tube amplifiers.

Transformers generally don't fail by themselves, they fail because of overload.

Michael

Tube gear is expensive because buyers expect it to be and sellers get whatever they can.

People don't buy tube gear for entirely rational reasons in the first place, and many buyers of tube stuff can be easly counted upon to fall into this category.

People who don't do things for entirely rational reasons can also be relied upon not to spend entirely rational sums of money.

Some tube gear is true vintage gear and so its price is jacked up like that of any other antique. There is demand for the item, not a lot of it around, and they stopped making it fifty years ago.

Non-tube vintage gear is the same way. Some old synthesizers from the early

80's still fetch surprising prices. I just googled "Yamaha DX7" "Craigslist" and the first hit wants a whopping $275 US. For the same $$$, you can get a synth that was made after Y2K, but for some buyers, that would be the "it" they are looking for.

Newly produced tube gear which is "like" that vintage gear receives a kind of rub off effect from this, like faux antique furniture that is expensive, though nothing special.

If someone made a faithful re-issue clone of that Yamaha DX7, they'd want an arm and a leg for it, you can be sure.

Tube amplifier quality is determined quite a bit by the transformer. If you can find an old tube high fidelity amplifier in a thrift store, then yes, you could rip out the transformers and make your own and hope that it would sound good.

If you find some crappy old dime-store radio in thrift store, then you're probably not going to get much better than crappy old dime-store radio sound in your amplifier.

All consumer expectations aside, tube transformers are boutique items that need a lot of expensive metal for the windings and the core, and are being consumed at low volumes. Even if they were selling 100,000 units a year, you'd still have to pay for the copper and the iron. Since they ain't selling 100,000 units a year, you're also paying a stiff premium to buy a low-production item.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com

** The first tube ( aka valve) amp put together was made entirety from scavenged parts.

Two 6V6s and a 5Y3 from old radios and a war surplus 6SN7 twin triode.

The output transformer was an AC supply transformer taken from another radio, the centre tapped HT winding did for the tube anodes and the 5V and

6.3V heater windings wired in series did for the 8 ohm output.

An 8 inch "electrodynamic" speaker provided sound and a filter coke for the HT.

Not really hi-fi - but sounded wonderful to me.

..... Phil

Mosfet amps get the best of two worlds IMO: they sound very close or identical to tubes and can be really easy to build. Not to mention they're a lot cheaper. They don't glow unfortunately, but something can be done about that:)

Greetings Tim, I understand about the boutique status of the amps and why this raises the price of the kits, tubes, and completed units. But I didn't know that the xmfrs were so special. Is there a simple way to tell if the xmfrs in a thrift store unit are any good? I suppose I could look for specific brand names. But is there any other way? Aside from the sound a tube amp would look cool on the shelf with all the glow. But I mainly want to see how one I make sounds. Eric

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The only way I know would be to make sure that the thrift store amplifier was pretty damned good to begin with.

There's a pretty marked correlation between quality and expense to an audio transformer, and always has been. Not very many people would have built cheezy equipment with really good transformers.

The only other possible way that I can think of would be to hook up with an old-time audiophile who happens to know if there were any brands or models whose transformers were better than the rest of the amp.

But I just don't think that you're going to hit the "audiophile" threshold in a thrift-store tube amp, if you could even find something in a thrift store with tubes. You may hit paydirt at an estate sale, or finding something on eBay that's trashed but has good output transformers, but I just don't think the local Goodwill is going to be your friend, here.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com

On 1/17/2014 11:53 AM, snipped-for-privacy@whidbey.com wrote: >But I didn't know

I don't know anything about tubes, but you may need to pick the proper tube for your transformer or vise versa. Take a look at these Ebay listings just to get an idea what is available, and prices.

Mikek

I think this is true. I see lots of junk at garage sales, but an "antique radio" or even that 1950s shortwaver receiver I got for $20 are pretty uncommon. Tube stuff has either been tossed a long time ago, or is now landing in dedicated circles. For that matter, I gather some places like Goodwill may be presorting, so if they ended up with a good tube amplifier, it may be sold through some other venue.

That's the nature of it. Something gets old, it becomes cheap, but few people want it. Then some time later, nostalgia kicks in, at about the same time scarcity becomes an issue. So the price goes up for what's still available. The time when people dropped stuff off at charity groups to get rid of it is long passed.

Michael

It's not absolute, but the bigger the transformer the better.

Look at a cheap All American 5 radio, the transformers aren't much bigger than you'd see in transistor radios (when transistor radios had transformers in the audio chain). They have to be limited in their ability to reproduce lower frequencies. A good amplifier from the tube age would have vastly bigger transformers.

Think about speakers. A tiny 2" speaker in a transistor radio has no bass, can't handle power, may not even be so good at handling high frequenies. Good speakers will be much bigger, and with a nice hefty magnet. It really is the same thing, since both the transformers and the speakers have to handle the full range of sound and the full power output, and are doing it at a low impedance (well the secondary of the output transformer).

Interstage coupling transformers can be much smaller because they are operating at high impedance, a very low current situation.

Go with Phil's idea, build the amplifier with plenty of space for output transformers, and until you find some good ones (hence the space for their eventual placement) use power output transformers. Not hifi, but it gives you practice.

Michael

The reason I mentioned thrift stores is because I do see old tube amps and radios for sale pretty cheap ikn thrift stores around where I live. There is even a recording phonograph for sale in a local thrift store. It has two arms. One for playback and the other for recording. It even has mike on a cord. I don't know where to find discs for the thing to record on though. Eric

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Transformer quality is by-the-pound ;-)

When I built toooob stuff, the transformers were "two-hands" worth. ...Jim Thompson

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If you can't find power transformers, or if you're married to the idea of "audio" transformers, look at tube guitar amp output transformers.

They're mass-marked (well, kinda), won't sound terribly bad, and the price is nice for lower power kit.

I've been kicking around the idea of a 15W/channel toob amp for my PC speakers, using guitar amp output trannys sitting on a chassis with enough space for the nice Hammond ones that Antique Radio Supply sells.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com

I grew up on toooobs, switched to transistors, enjoyed _damping_, never looked back. ...Jim Thompson

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| Analog Innovations                               |     et      | 
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I love to cook with wine.     Sometimes I even put it in the food.

Yeah, Phil previously remarked that modern strip-wound power toroids work supprisingly well in the audio band, so that's possibly a better (and easier) option than re-purposing an old toob power transformer.

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Take a look at the audio power amps starting on page 694: 

http://www.tubebooks.org/tubedata/RC30.pdf 

JF

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Good tubes never were cheap. A good set of matched EL34 for instance can do a $50,- and you need two set for a stereo amp.

The real expensive parts are the output transformers. Good transformers always were expensive and they still are. But where the quality of tubes degrades (cheap Russian and Chinese production) and there has not been any development for decades, transformers stil became better over the years and much more expensive. They can easily do a $150,- a piece. Still cheap compared to types with silver plated wire. Some people say they hear the difference.

So if you find a good tube amplifier you'd best try to restore it. Otherwise you may use the power supply and the output transformers to build you own one. Real good amps (matched tubes, ring core transformers) can be bought over here for a E1000,- though I doubt *I* will hear the difference between that one and a E500,- type.

petrus bitbyter

Not when I was a kid, IIRC ~$8 ;-) ...Jim Thompson

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| 1962 | I love to cook with wine. Sometimes I even put it in the food.