Top tips for buying a used tube amp?

Related to another recent thread…

Being an absolute novice when it comes to tube amps, and about to start looking around on the second-hand market for options, I’m wondering if there are any tops tips on what to look out for please.

Things that have crossed my (possibly over-thinking!) mind include:

- Servicing: how often should tube amps on the whole be serviced? Is it sensible to avoid ones that haven’t been serviced in x years? – and would one that hasn’t been be underperforming, even if it sounds ok? Or should they just be taken at face value (sound), irrespective?
- Tube rolling: are there any common mistakes people might make on swapping tubes? Some ads say uprated tubes, but without giving detail. Anything to be wary of there? Rules of thumb for mismatches that show someone hasn’t understood the product etc
- How would you know tubes are old and need replacing?
- Any general warning signs to look out for on the condition of an amp? Alarm-bell-ringers.

Any advice much appreciated.

Thanks.
Rob

 

RE: tube rolling

This is where I think the savings can be had. Most folks roll in tubes that are mediocre at best and usually fall into the poor category. Tubes can get real pricey and you can get a feel for what they spent and what they could have potentially spent. If someone has recently re-tubed it, see if they had someone else bias the tubes. It probably would have been looked at for associated problems or trouble spots. And ask if they'll keep what they bought and you will re-tube it yourself. Then, do homework on what would work with the amp/type of music you listen to/other equipment in the loop.

The thing to remember when buying tubes is that nobody, and I mean nobody, claims they do not have good midrange. It's like fresh seafood---know anyone not selling fresh seafood?

 

Unfortunately, every one of the things that you are concerned about are in fact, simply the risks of buying a used tube amp. Only a warranty will protect you from a service trip fee, a tube replacement set, etc. In general, I consider the cost of a service trip and a new set of tubes (at least the output tubes) as part of the cost of the amplifier when buying used. I service my own amps, which is what I do do professionally and so almost every day for others. The best approach is to save for a new unit or to buy your used unit from a trusted source. Pretty much all tales of "hours" on tube sets, "service history", etc can be taken with a lump of salt when described as such by sellers. You must assume none of that is true and that it will be your responsibility, because it will be your responsibility. As for vintage amps, they all come with this risk, period. Condition is everything, and condition cannot always be assessed by cosmetics. Operational condition just comes from observing the amplifier in use.
-Bill

 

Make sure you are well-acquainted with a competent tech before going down this path.

 

Get a used Prima Luna, nothing to play around with or maintain.
My Prologue 2 is built like a tank, and my Winged C KT88s and Tele/Mullards ECC82/83s
have at least 3000 hours on them and nothing has failed, the stock valves are a bit meh
but fine to get you started.

For years before this I battled with Quad II's and various pre amps, it was like owning
an old Alfa Romeo.

The Prima Luna is more like a new Honda.

If sound quality is number one priority then look at Croft, made in UK and killer sound.

 

Self-biasing.

 

The first priority is sound quality sure but you also need something somewhat reliable - but you don;t want somehting that sounds mediocre and is ultra reliable - you could just buy a Bryston for that.

I have owned my Audio Note OTO Phono SE for 11 years and I've paid $8 for a blown preamp tube over that time. Here is why my vote goes to the Audio Note OTO Phono SE (or the non phono version if you don;t have a turntable.

Pros:
1) It sounds excellent - you'll be hard pressed to find a better sounding amp under $5,000 or perhaps $10,000
2) It is self biasing so you never have to buy voltmeters or make any adjustments when you put new tubes in the thing. Indeed, this applies to all Audio Note amplifiers.
3) The OTO uses long lasting and very affordable tubes - The tubes will last in the 8000 hour range and being EL84 output tubes - they're cheap as chips to replace - even some of the more exotic or deemed "good" EL 84s are not as outlandish as other tube types.
4) Better than average resale value. Indeed I can sell my 11 year old OTO Phono SE for MORE than I paid for it. WHAT? Yes - and the reason is simple - Audio Note doesn't change models but the prices rise. So an OTO sold in 1998 for X dollars is now being sold for about 2-3 times the price new. You put yours up for sale at half the NEW list price so people say what a great deal - and it is - but the original owner is getting his money back. As soon as a model changes or gets discontinued the product's value usually tanks.

Cons:
1) Understated looks that don't show off the tubes. If you must see the tubes - this can be a let down
2) 10 watts of power - (4.2 watts per channel undistorted). This is a low power amp and requires somewhat careful matching to a high efficiency loudspeaker 90db AN K/Spe as a kind of minimum.
3) No colour option - black with gold knobs - the new sig model comes in Silver.
4) Leans slighly to the warm side of neutral - but IMO that's kind of the point of buying a tube amp over SS. The more expensive models retain the sensations and adds more resolution but the price typically goes up 5 times so...

 

Well, if you're talking about a really vintage piece -- 20, 30, 40, 50, 60 years old -- you're talking about a piece that is going to need or has had a lot of maintenance work over the years: electrolytic caps will have to have been replaced; the innards of tube amps are hot envirnoments which can help hasten the demise of any given part -- caps, resistors and even circuit boards and solder joints. 50 year old parts might just fail or drift out of spec anyway, they all need to be checked out and, if out of spec, replaced. Some older pieces might use things like selenium rectifiers in bias circuits, these need to be replaces with silicon diodes. Stuff gets dirty -- pots, tube sockets, connectors -- to the detriment of audio performance. These things need to be cleaned or maybe replaced, tube sockets might need to be retensioned. And if a really old tube amp hasn't even been turned on in years, it need to be brought up to full voltage operation slowly on a variac before it can even be tested.

For a novice who has no experience or knowledge in repairing or trouble shooting vintage stuff, I'd recommend either staying away from it entirely or only buying a fully restored piece from a good tech who offers a good warranty on his or her work. Buying an old piece and having a tech rebuild it (or even rebuilding it yourself) can quickly become a money pit for the uninitiated, and depending on where you are, finding a tech who actually knows what they're doing can be extremely challenging, and some of the stuff you see for sale -- with rusted iron and toasted circuit boards -- probably isn't worth buying at any price even if you know how to fix it yourself given the cost of replacement iron.

If you're talking about a newer piece that's been well-maintained and in more or less regular use, I wouldn't worry too much about anything other the same things you'd worry about buying any used piece of electronics. Electrolytic caps will need to be replaced eventually -- as they will need to be with solid state amps -- so it's not a bad idea to have a tech who can give the piece a once over and possibly a cap job, but after that initial pass/servicing it might run for a decade or two without needing additional service.

Of course at some point tubes will need to be replaced. Now, I wouldn't worry too much about tube rolling for sound to start -- get to know the sound of the piece first. Although there are some pieces that are hard on driver tubes and phase inverter tubes, for the most part in tube hifi circuits the small signal tubes can last years and years, even decades. Output tubes will have to be changed more frequently and if the amp you buy has a fixed bias (vs. cathode biased) output stage, you'll need to bias the output tubes when new ones are installed (cathode-biased schemes don't require a bias adjustment by the user). Setting output tube bias may be a relatively easy chore requiring just a screwdriver or a screwdriver and a multimeter; or getting access to the bias adjustment may be a little more complex (as it is, for example, in a lot of vintage guitar amps where you have to remove the amp chassis from the cabinet). Either way you will need to learn what is the appropriate bias point for the output tubes in the particular circuit of the amp and you'll have to learn how to set it or you're going to have to take the amp to a tech everytime you need to (or just want to) change output tubes, which is a bit like taking a guitar to a tech every time you need to change strings, not really a practical solution.

You should keep spares around anyway so whatever you buy I'd get a fresh set of decent new production tubes of some sort (lots of choices, not a lot of great choices), and install 'em and keep the stuff that comes with the amp as spares unless what comes with the amp is great vintage glass in good operating condition to start with.

Warning signs to look for -- toasted and charred looking parts and circuit boards, noisy pots, rust on transformers, bulging capacitors, hum, that sort of thing.

 

In order to advise you, it would help to know how much you are willing to spend - now, later, plans for other equipment, gear you already own, etc. Do you have speakers already that you want to use or will you be buying speakers? It would also help to know what tube amps you've seen and/or heard that you like - think you might like. Also, do you need a system for a small, medium, or large size room (do you need a low or high power amp)? Do you want old, new, or newer used equipment? Do you want a small simple integrated amp, or a large system with a preamp amp and power amp(s)? Do you like to tinker with gear? Do you have any reputable service techs near you with knowledge and experience with tube amps? If you think you want to jump into the tube amp game, these are things you probably need to consider before you start spending money.

I absolutely love tube amps and have many of them (15 or 16, I think - audio and guitar amps). I've been playing around with them since I was a kid (45 years at least). I really don't have a problem with maintenance, or tubes burning up and needing to be replaced - but I only purchase quality NOS (new old stock) or nearly NOS tubes (not cheap). The only problem that I've had is occasionally a capacitor will go bad (I'll notice a hum or buzz that won't go away), and I'll have to take it to my tech for repair. I'm fortunate to have a truly great tech but he's about a 45 minute drive away - but I only need to take one or two of my many amps to him about once every year or two. In other words, I have many tube amps that have been operating perfectly for many years without any maintenance.

I prefer listening to music through tube amps but I'm also a gear fan, a tinkerer, and consider it a serious hobby. If you have the desire, interest, time, and some money to spend, I say go for it. Don't be discouraged by stories of endless trouble, maintenance, and expense. I haven't found these things to be nearly as much of a problem as some make them out to be. No doubt some people have had a bad experience with a tube amp - but a lot of people have had great experiences using them and wouldn't use anything else.

 

Thanks Richard - useful pros and cons. I actually saw one of these advertised, used, recently - phono version, £1,400 - and did wonder, as I know they have some strong supports on this forum. That particular price was a bit north of what I wanted to spend right now, but more so - would it really be enough to drive my speakers properly? ProAc Studio 140 mkII (91 db) - which I don't really want to change to be honest. Again more than I intend spending, but worth considering if it really would be buy and forget - if sufficient oomph.

 

Somewhere there's a "chart" that shows you need X power for speakers of Y efficiency to get dynamic peaks of W, etc. etc. People love to break out this chart on McIntosh forums to demonstrate why everybody needs a 300 watt behemoth of an amp for music to sound right.

My real-world experience says this chart is basically useless. 91db speakers should be able to blow the roof off your home with pretty much any well made amp.

 

If you buy a used tube amp, be sure to immediately have it inspected by a trusted and extremely competent tube amp tech. If you don't know one, you may need to spend as much effort finding the tech as finding a suitable amp to buy.

When you buy any tube product, in my experience, be prepared to replace all the tubes. It might not be necessary to replace them all, but then again, it might. That must be factored into the purchase price. Depending on the amp, tube types and quality, this might be as much as $1000.


Also, other parts such as capacitors may need to be replaced in order to ensure optimal performance. Some service may need to be done just to ensure that the amp is safe to operate. (don't want any smoke or fires). What might that cost? Could be $100. Could be $500...

 

Car analogies work for me! Funnily enough I was also just looking at a used Prologue 2 for sale, and reading up on them. Seem pretty universally liked and the reliability aspect is often mentioned, as it the adaptive auto bias. Oh decisions, and a new world of potential pitfalls. But it's great to hear your first-hand experiences - thanks.

 

Excellent advice - thanks for taking the time. I'm not looking for vintage as such - should have mentioned that. Something newer, and hopefully relatively idiot-proof. Actually getting to understand all this stuff - ins and outs of a tube amp: its components and design - is something I'm really interested in over time, but really don't want to start off with a project. And I don't personally know any techs who could help. Lots for me to consider here - cheers

 

Alrighty:
- As just put above - speakers ProAc Studio 140 mkII (91 db) - don't want to change these. All other current gear in my profile.
Budget c. £1,000. Room size 250 sq ft. Want an integrated amp. New or used. Not a natural tinkerer but practical - but as above don't want a project to start with. Though happy to put money in along the way. No plans to change other equipment yet. Next thing likely the phono stage, but no rush.

Everything you say is ultimately encouraging - thanks.

 

That's good to hear. I bought the ProAcs with sensitivity and the potential for tube amplification in mind. And it was pretty amazing to the hear the immediate lift in headroom over the ones they replaced (Castle Howard S1s) with my current amp.

 

Sound food for thought - thank you. This tech person thing keeps coming up... seems like I should start trying to find a good local one...!

 

I really like old amps: My last pair of ~1957 vintage amplifiers - Eico HF-60s - were rebuilt with new power supply and coupling caps. Easily the best push-pull amplifier I've ever heard (after a few mods) but that was due to the classic Mullard topology, tube choices, and the excellent Acrosound output transformers. Tube amps - at least competently designed ones - are fairly rugged beasts. I've been playing the vintage and DIY tube game for 25 years now and I've never had one completely destroy itself. It does happen though - like a friend who had a Heathkit W-5M power transformer blow, flooding his listening room with smoke.

As mentioned above, an older tube amplifier usually needs a recapping job - either the ancient electrolytic power supply can cap, or another possibility are leaky oil capacitors. Even a 1980s or 1990s piece, like a Audio Research D-76 or a Conrad-Johnson MV-75 will be due for a look over from a tech.

The Pro-Acs sound efficient but I would be curious about their impedance - and how far down they dip. ie - are they really suitable for tube amps? Some speakers just seem to work better with SS gear so I would research this before making the tube amp plunge.

Since you're in the UK, I would be looking - if you wanted vintage - at a Leak, or a pair of Quad II monoblocks, Radford, or (ha! so rare) Lowther monoblocks.

 

The problem is that techs bill by the hour, and it's very time consuming. From having read dozens of people's stories of rebuilding their McIntosh amps, it seems the best case scenario is when people have the skill set to do the work themselves. Another problem is that some techs seem philosophically opposed to replacing components that haven't failed yet - the emphasis being because if we're talking vintage, obviously a 40-50 year old capacitor that hasn't gone yet is a ticking clock. And as I understand it, transformers can't really be replaced, when they're done they're done.

This is why really I'd probably avoid the vintage + refurbished route in most cases. I've gone down that road with mixed results.

 

Personally I recommend just starting with a tube preamp and see how you like that experience before going all-in for tubes. I've been running tubes in my system for about 35 years, and about half of that time I ran a tube amp, and the other half I ran SS.

The advantage to this approach is that you can get about 80% of the sonic benefits with about 20% of the reliability problems. Plus its a whole lot cheaper to roll preamp tubes than it is to roll output tubes in an amp.

But what others have told you is true: If the previous owner has not serviced a vintage piece, then you WILL need to do so. Period.

 

Chervokas has already covered a lot of the important considerations for vintage tube amps. The only thing I would add is to be cautious how a used amp is advertised. "Serviced" is not the same as "restored." A serviced amp is usually one that has been checked for any obvious failing components and repairs have been made to get the amp functional again. A "restored" amp often goes beyond that and replaces any components (capacitors, rectifiers, etc.) that are likely to fail in the near future, even if they are currently operational. A good restoration job should set the amp up for another 10-20 years of continued use, with perhaps only the need to change out failing tubes.

If in doubt, ask for a list of repairs/replacements to see how much work has been done. There may still be "ticking time bombs" within the amp that will need attention (selenium rectifiers and eletrolytical capacitors being at the top of the list). If you end up buying some of the more well known vintage brands (like Fisher), there are dedicated forums for them over at Audio Karma. They should be able to help you with any questions that arise.

 

Balanced Audio Technology's tube stuff is probably up your alley. I have vintage Macintosh MC60s but if one went down I would go to BAT. Circuitry is balanced and solid.

 

Get a good, reputable tech and they'll restore it right and replace all the caps, resistors that have drifted, any bad sockets or repair them and any rectifiers. They can also install a few minor mods that will make the amps last longer like in rush limiters and dropping the voltage on output tubes a bit. As long as you don't loose a transformer due to a tube blow out they'll last a long long time. They're are also places that can rewind transformers and parts units yo be had for most popular vintage gear. With a little care I don't think you can go wrong with vintage gear. That being said there are plenty of great modern tube amps you can get used like Manley Stingrays, Leben CS300s, any Decware amps you might be lucky enough to come across. Currently I'm running a Fisher 500c and it is amazing. Destroys the Jolida and Cayin amps that I've heard. That being said my next amp will be one of the above mentioned integrated amps.

Mistakes I've seen people make usually come down to trying to save money. Tube amps are not cheap when compared to solid state ones. Vintage requires thorough restoration and that can be pricey. Counting tubes I've seen people pay close to 800.00 to restore Fisher and Scott amps. Still well worth it in my opinion. I've also seen people get half *** jobs done that have resulted in blown amps and speakers. Then you have the cheap Chinese tube gear. Most of which I think is junk. Sound bad and very poor quality. I've seen a Cayin amp die after a year and a half of use and the support was non existent.

Oh and I'm keeping the Fisher, would never ever sell it. Just grabbing another nice amp to mix things up.

 

Since you are in the UK, I would go and find a couple of nearby dealers for Icon Audio. These are new tube amps based on vintage circuits and have fair build quality. Since they are new, you are not facing the issues of condition or replacing tubes. You will also have a warranty. Buying from a shop who also has an in-house tech who is good with tube gear would also be a plus. They have two models that might best suit you. They are integrated amps, so it's a complete package. The Stereo 40 MKiiiM is $1500 pounds and the best for your speakers and to get a good grip on all types of music. They also have the very similar, but lower powered Stereo 25 MKii at $1000 pounds. Dealers who sell these might also have other brands to choose from, may have some trade-in models from the same or other brand, and possibly have an in-house tech. That's pretty hard to beat for a first time buy. I sell the Jolida brand here in the US and offer in-house service and it is very similar to the Icon. You certainly get access to better products when you step-up the investment, but these are good entry points for those who have limited funds. If you can listen to some tube amps and are really sure that is the path that you want to take, going ahead and getting a better quality, domestic unit is the best course of action. I carry Rogue Audio for that, which is also available in the UK. Another UK brand that can be found new is Croft and that would likely also be a step-up. The rest of your gear will make an investment worth it and will sound way smoother than your present amp. Your CD player will compliment the tube amp wonderfully.
-Bill

 

http://www.audioaffair.co.uk/icon-audio-stereo-25-mkii-valve-amplifier