It's been a while since I ran amps that required biasing, but my approach was to start at the low end of the builder's recommended range. Then, in part because I'm lazy and because I want to be gentle on the tube. I would just leave things be and not bother to check the bias. As the tube ages, the current flow drops on its own so the bias point drops. By not changing the bias to compensate for the drop, i am actually preserving the tube, albeit with a small loss in output power.
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The designer and builder of our monoblocks uses the same Dodd Balanced Power Supply to power his builds that we use to supply power to our system. They makes exactly 120 volts at 60 Hz. The 75 lb. laminated core transformer takes whatever comes from the wall outlet and makes a +60v and a -60v rail, both at 60Hz, and then joins them at the outputs. The amps are optimized for KT77 output tubes and can run no other type of output tube. I foolishly tried all of the usual suspects, even though I was told by the designer/builder that it wouldn’t work; he was right, can’t get any other output tube type to bias correctly. Had a lot of Octets for sale for a while :). Anyhoo, I feel very lucky about the amps being designed and built based on the same power supply; apparently, pretty darn optimal. Accordingly, I’ll say again, for tube amps, it’s worth using a Balanced Power Supply (or, I think, a power regenerator) to assure that your amp(s) see 120v at 60Hz. |
The only thing that can come to mind about making your power tubes last longer would be to set their bias a little under than the recommendation for the amplifier. This will not hurt the amp or the tubes in any way. The manufacturer has a recommended set point for where the power tubes should be biased to get the best sound and operation from the amplifier but by adjusting the bias to your liking, you might be happier. And by dropping it down a bit under the recommended set point the tubes with be running a bit cooler and should last a little longer. . Some people choose to run their tubes hotter which burn them out sooner and others run their cooler which makes them last longer. You’ll also hear a difference as you adjust the bias. I’ve experimented with this on my Canary 301 mk 2 300b amplifier yrs ago. |
@cleeds I stand corrected. However if the line Voltage is consistently 126V you'll find that tube life is curtailed with many tube amps and all if they are vintage. I recently worked on an Eico tube amp that was 'eating tubes'. The amp was built when '110V' was the norm. The output tubes were conducting way too hard. They were cathode biased so I was able to change the cathode resistors and calm things down. |
What is "normal" is not necessarily ideal for tube electronics, particularly vintage gear that was built for lower voltages that were prevalent when they were made. As I mentioned above, my local dealer who only sells tube amplification often has customers measure their outlet voltage and then orders the right transformer for them to use on the outlets supplying their amp and other tube gear. He prefers to run the gear at much lower voltages than is common. This is usually the cure for premature tube failure. He also has his customers bias amps on the conservative side. This is consistent with Atmasphere's recommendation. My normal voltage has been, for the longest time very steady at 117 volts at the outlet, but has recently crept up to 119-120. My amp is cathode biased so I cannot do adjustment, but typically, cathode biasing means conservative levels. If my voltage rises more than this, I too will consider a transformer. |
If you’re talking about the US, you are mistaken @atmasphere. Nominal voltage in the US is 120VAC ±5 percent, so anything between 114VAC and 126VAC is normal. That is established by ANSI C84.1 standard. Note that the spec is measured at the service entrance - it’s common to have some voltage drop at the AC receptacle. That’s something dedicated lines can help limit.
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Ralph, thank you. It appears that I do everything right. There is no standby switch. Voltage is regulated by the regenerator, I hope it is. Ventilation is excellent from all sides. The amp seemingly drives the speakers with ease, no stress that I can perceive. The tubes are clean, no fingerprints. I might try to lower the bias a little and see what I hear. |
@inna For longest tube life: 1) keep the tubes clean and free of fingerprints. 2) keep them biased properly, if you can run them a little below spec. This works only if the sound isn't adversely affected. 3) use the Standby switch to warm up the tubes. If you don't have one on your amp consider getting one installed. A standby switch cuts off the B+ (DC high Voltage) for the tube. As its warming up, if the plate supply Voltage (B+) is present, you get a phenomena called 'cathode stripping' where the cathode coating gets eroded over time. So a standby switch can prevent this. 4) don't push the amp hard. In a class AB amp (most EL34 amps are class AB) the harder you push the amp the hotter the tube gets and heat causes it to wear faster. So make sure your speakers are easy enough to drive that the amp is loafing nearly all the time. 5) make sure you have adequate ventilation. Again, heat is the enemy of the tube. 6) Make sure your speaker is connected to the right output transformer taps. So a 4 Ohm speaker should never be on the 8 Ohm tap; that would cause the load on the power tubes to be much lower, causing some of the power they make to be dissipated in the tube rather than the speaker- so yes, they will run hotter, put out less power and make more distortion. 7) make sure your line Voltage isn't running high. 120V is normal now and the line is not supposed to exceed 125V for more than a second. But I've seen situations were 125V was normal and unsurprisingly the customer was going through power tubes a lot faster. 8) the controversial and last thing: Some amps push power tubes harder than others so go through tubes faster. You might want to take a thermal camera to see how hot the tubes are running and compare that to other EL34-based amps, or use the internet to see if there's a correlation with certain amps that tend to go through tubes faster. Follow these suggestions and your tubes will last longer. |
Jerry, you are right. Anyway, the best way forward is to have more spare tubes ! mulveling, I think I am done with audiophile expenses for this year, But..let me see..maybe I can cut the expenses somewhere else. This is a disaster. I saw those Sylvania on ebay but I will wait - currently installed RCA black plates from early 50s work very well, no complaints. Now that I am going to have better Mullards, I suppose I will not accept anything less in the future. It is either XF2 or XF1 Mullard or perhaps Amperex Holland. |
@inna I wouldn't say that I recommend choosing an amp that is easy on tubes so much as I recommend against an amp that is hard on tubes. How do you know which is which? I'd say avoid an amp that gets more power than normally attributed to that tube--unless I needed that power and was willing to buy tubes. And I'm fine with that. Personally I don't think tubes are expensive compared to the rest of the audio equipment we all have to purchase. I buy tubes when I don't need them. A nice pair of Hytron 801As showed up yesterday. There is a trend now to make higher power tube amps to drive lower sensitivity speakers. I like higher sensitivity speakers but if you're married to your 92-95dB speakers and want to drive them with a tube amp, you need more power. So they are making more push pull, parallel SET, and High power SETs with the higher output tubes. if you buy some of these, recognize you'll have to replace tubes more often. (not saying push pull amps are hard on tubes, unless designed that way). If I'm looking at a 300B SET and the OEM says 8 wpc, and 300b's generally do 6 wpc, I'm going to wonder about tube life. (or else the marketing talk is exaggerating and it really is a 6 wpc amp). I've found that if you go with an amp builder with a lot of experience and knowledge, they are likely to design their amps conservatively. And if you call Aric or Apollo and order and amp, if you tell them to use conservative parameters to promote long tube life, I'm sure they can do that. jerry |
Nice! Enjoy - great tubes. Don’t worry about the exact hours on ’em. A meaningless metric, now. "They don’t make ’em like they used too" applies, etc and yada yada... For Amperex / Hollands I’ve only used the xf4 and xf5 models, both with the brown/red-base. They both sound equally great - I’ve even mixed them in quads (matched pairs), with no problem. The older metal base Philips / Holland version is supposed to be extra special - I’ve almost pulled the trigger on these in the past, but never did.
Why not? I expect 1950s black plate Sylvanias should be very good. I generally prefer these over any RCAs, though I haven’t tried the 12AU7’s. You can do 5814, 6189 and 5963 subs too. The 5963 tend to be microphonic, so those should be relegated to amp driver slots only (NOT the preamp or phono slots). RCA black-plate 5963 was the favorite 12AU7 sub for early 2000s-era VAC power amps. |
Found them ! Matched quad of Mullards EL34 XF2 is coming this way. It's a little risky because they are not new and the exact number of hours on them is unknown, though supposed to be low enough. Test as strong NOS, as the seller with excellent feedback says. It's always a gamble with tubes to a degree, I feel fine about it. |
The 60’s Mac amps also very famous for long tube life… I have some 1965 tubes … Tele that still test well.. @whart I need to copy your dusting rigor…. wow…. i would never get away with photo like that….. |
Your bias current is usually measured across a 1 ohm resistor so that mV=mA. The meter measures volts but because the resistance is 1, then the number is the same. So a custom meter will measure volts, but it will say amps. if your maker didn't order a special meter dial, it may say mV, but is actually reading mA. There is a post above that contradicts this and I'm not sure what the poster meant. Jerry |
Yeah, miss Roger Modjeski - what a treasure he was. He was the master of tube conservation. Gave me a good tongue lashing for biasing my RM10 wrong and set me straight for an hour on the phone. Never wore out or shorted a tube in over 10 yrs on my unit. Sorry I sold my RM10MkII. He wrote on his forum "don't worry about handling tubes w/bare hands just get the peanut butter off your fingers". Just got a matched quad of EL34's from RAM tubes yesterday. |
Reducing heat by venting the component or cabinet can extend tube longevity. Suggest that you visit; https://acifinity.com for a wide selection of component/enclosure heat extraction units. I have one of their units placed directly on top of a Prima Luna EVO 400 integrated amp. It's like they are made for each other. It drops the temp around the tubes by about 12/15 degrees. Btw since these are extraction units rather blowing cool air onto the tubes there is never a risk of thermal shock damage to the hot tube. Enjoy the music.. |
Sure, that’s a fine strategy - stick to seeking what you really want. But I’ll say that even XF3 and XF4 Mullards were much much better than SEDs, to me. I didn’t really like SEDs; they came off as a 1-trick pony for lots of warmth, lacking the articulation and 3D holography of British Mullards. That seems to be a common pattern with modern tubes, or Solid State components that try too hard to emulate the vintage "warmth". You could get some nice XF3 / 4 to use in the meantime, and then they become great spares when you get those XF2’s :) This is how I ended up with tons of tubes lol... |
I see. Before 60s Sylvania were good, I’ll keep it in mind, thank you. Kevin didn’t specify, by the way, he just said Sylvania and Brimar. Brimar lacks Mullard’s sophistication and has a recessed midrange, both are no-no to me. No, I’ll get XF2, believe you me. I made a mistake after I bought the amp by getting SEDs instead of seeking out Mullards. I’ll correct this mistake. I should’ve listened to Kevin about that and had more patience. |
Sure - the sonic traits of one make/vintage of 12AX7 generally carry over to the corresponding 12AU7. Sylvania tubes seemed to change a lot from the 60s onwards. Before 1960s: nice clean airy sound, great dynamics, with a beautiful midrange that was romatic and organic while not so thick & warm as Mullard. Afterwards - a more bright and solid-state like sound. Ending with Philips ECG tubes of the 1980s (ugh). The later tubes are certainly serviceable, and even good in some roles, but older Sylvanias with black plates are generally much more desirable and sound good almost anywhere. You might think of older Sylvanias as (sort of) like USA’s Siemens. XF2's are excellent. I had a quad but they were well worn when I acquired them. They were perhaps a bit more articulate than XF3 and XF4, but don't sleep on the latter - it's far easier to score a really nice quad of those, with a lot of life left. |
When I bought the Avatar I talked to Kevin about tubes. He recommended selected Chinese 12AX7 for the preamp and phono that he had, Brimar or Sylvanis 12AU7 vintage for driver and, yes, Mullard or Gold Lion vintage for power tubes. But I didn't want to go with any Chinese, I didn't like Brimar 12AX7 in the phono and thought that 12AU7 would not be too different, and Sylvania is thought to be bright by some. So, I disregarded his advice and went with 12AX7 Mullard long plates and 12AU7 RCA blackplates, and I am quite happy with the result. But for power tubes, yeah, Mullards are going to be installed soon enough. |
It would certainly be interesting to try vintage Amperex EL34 but I am currently on the hunt for Mullards XF2 and getting close to them. XF1 would be much more expensive and even more difficult to find. Then there are first generation Mullard EL34 with metal base that some people consider the best. Well, probably impossible to find a matched quad or at least pairs in excellent condition, so I'll just forget about it. Unless I get very lucky. Yeah, probably "inferior" was a wrong word not always accurately reflecting the difference. Of course, SED Svetlana Winged are a copy of Mullard, sound signature should be similar. |
For bigger KT tubes, it’s extremely hard to find good vintage ones anymore. There are still some late make GE 6550s out there. EL34 (like your amp uses) and 6L6GC is much more feasible for sure. The British Mullards are warm (like your SED / Winged C, but better); I preferred Amperex / Holland EL34 for being more a bit more neutral while still sweet sounding. The East German RFT / Siemens are supposed to be quite good too. Electro Harmonix EL34 is a copy of this tube, at least superficially - but the old RFT build quality was much better (straight glass bottles, even!). I’m quite fond of many of the Russian power tubes so it feels wrong to call the "inferior". But yes, the old power tubes were generally better. The old EL34 were beautifully built. Also remember - part of VAC’s "secret sauce" is Kevin’s voicing expertise / craft, and it’s usually advisable to stick with tubes that sound at least similar to what it shipped with. What does VAC recommend for an Avatar these days? They were shipping Shuguang KT88 power tubes in 2000s (some with Penta Labs labeling), but Shuguang is long gone. I have a VAC 450S that originally shipped with those Shuguang KT88. They wore out before I got they got. Russian Gold Lion KT88 didn’t sound good in it, but fortunately Tung-Sol KT120 do :) Now that I think of it, might be worth tracking down some Shuguang KT88, sometime. |
Alright, I will join you in the abandoning the ritual of using white gloves while handling tubes. And the grip is indeed worse than bare hands. Having extra set of all needed tubes is of course always a good idea, well, some tubes are really expensive and hard to find, at least from reputable sources. I am not going to use any new reissues, only interested in vintage tubes. I see no reason to just waist money on inferior sounding and less reliable tubes. But if you need 20 power tubes, yeah, you just might be forced into that. I only need a quad. |
Yes, the concern over skin oil has to do with light bulbs, not tubes. The oil deposited on a high intensity, high temperature light bulb will carbonize from the heat. That leaves a black spot on the bulb. The light from the bulb is absorbed by the black spot instead of passing through and that makes the black spot MUCH hotter than the surrounding part of the bulb causing that spot to fail. Another piece of advice is to grip tubes which have a base by the base and don't push and pull on the glass envelope. The concern is accidentally separating the base from the glass envelope. Also, if you do a lot of tube rolling, be aware that tube sockets have a limited life in terms of how many insertions and removals before the connection becomes less reliable. An old time technician told me it can be as little as 30 insertions and removals for a socket to fail (i.e., cannot be re-tightened reliably). If you do a lot of trials, consider using socket savers while you are trying to find the right tubes. |
As Roger Modjeski well understood, the SOE safe operating envelope for a specific tube is not a few points… hence a deeper understanding of both amplifier design with a dual focus on reliability and sonic engineering… the now ancient RCA SOE diagrams and tables yield much for those who do not think only in terms of points.. see RM-10 for imo a phd “ amp camp “ level demonstration of what is possible in terms of output, reliability and sonics.. RAM tubes and the testing…few if any can do contribute significantly as well… RIP… i miss him, could hardly wish for a better mentor, sensei, spirit guide… |
Agree on the gloves point. Actually, this is something that the engineer in me screams "you're solving the WRONG problem!" about. There is NO risk to tubes from skin oils. Audio tubes are nothing like those awful halogen bulbs from the 1990s. The biggest risk to a tube is DROPPING it. And guess what - those cheesy, cheap white cotton gloves are generally very slick compared to a natural grip. So while purporting to protect tubes from (harmless) oils, they actually introduce a REAL risk to your tube handling. Ugh. These gloves should all be burned.
While I do love the ability to manually adjust each tube bias point, the VAC iQ auto-bias system has been very, very good in my use and sounds excellent. |
@whart made a couple of points that I agree with. I check the bias frequently. I don’t have to use a fluke meter as my amp has meters for voltage and current for both the driver tubes and the output tubes. My amp is very stable but I have been rolling tubes a lot lately. I also agree that there is no need to use white gloves. I’ll admit I’m an outdoor guy who doesn’t use lotion so my skin tends to be dry. but most tubes run cool enough that a little skin oil it isn’t a problem. Thinking about this thread for the last day, I think the biggest factor in tube failure is running them at the wrong voltage or current. Most amps don’t have as much adjustability as mine. I’ve had amps with no adjustability (cathode bias) and they are designed to be easy on tubes--no action required. I had a Decware ZMA and it had a great biasing system that I really enjoyed. it accommodates a lot of tubes and the bias current for each tube can be different. to calculate the bias current for a particular tube, look up the maximum plate dissipation on the tube data sheet (watts). Measure the B+ voltage of your amp. The best way is to use some insulated probes clipped to the correct pins (tube slightly elevated) running out to a volt meter. Make sure you don’t create a short to the chassis, turn your amp on, write down the voltage, turn your amp off and remove the probes. This number is important to know. Sometimes OEMs will provide it. Divide your plate dissipation (watts) by B+ voltage (Volts) will give you amps. You’ll have a decimal. Multiply by 1000 to get milliamps. Now decide how hard you want to drive your tubes--usually a number between 60% and 80%- and multiply that times your current and that is where you set the bias. I have found recommended bias numbers well above what I calculated. I have also know guys who ran their bias purposely higher than recommended because they thought it sounded better. I think this is a myth, the "higher must be better" mentality. If you have auto bias, you’re out of luck. I’ll never buy an amp with autobias. Jerry |
I agree that most tube amps sound good after a short warm up, it takes solid state gear more time to sound good so I can see why people keep solid state stuff on all the time. There is no good reason to do that with tubes. I also agree that many manufactures push tubes hard. I think they do that in order to claim higher output. It seems crazy, to me anyway, to prioritize high wattage ratings with tube gear. I run some very exotic, and very expensive tubes in my gear. Fortunately, the tubes are run very gently and I have been using the same tubes for close to two decades and the tubes were already old and used before I got them (they tested good). The only tubes that have ever failed on me were twin 300B tubes that are used as rectifier tubes in my phono stage. They failed because a shelf collapsed and dropped a 15 lb turntable motor controller on top of the power supply to the phono stage. |
On/off cycling the worst, in rush current at initial startups hard on tubes, rectifier tubes and/or soft start circuits, rectifier tubes may be sacrificial here. Heat is the enemy of all components, my 845 SET amps, nearly 1000V at plates, cooling fans beneath amp to push heat out, 300B amps much less stressed by the heat. Quality tubes with good reputation for reliability.
Some amps just harder on tubes than others, some manufacturers really push with high plate and/or heater voltages. Do your research on amps, determine whether there is history of failures, this is number one with me. For some years I was having failures with a certain tube, replaced loosely spec'd resistor in heater circuit with much higher spec resistor, no further problems. |
Really, don’t overthink it. The lifespan will be determined primarily by the amp’s operational parameters (bias, voltage), and quality of the tube. Enjoy your tube amp. Vintage tubes tend to be very good, and long lived. But these days, most of what’s left there are used and will have unknown hours (many???) on them already. Russian power tubes have been very good for me, but they do fail occasionally, and yes "spectacular" failures (catastrophic short) can happen and take out a resistor. Replace those tubes every 2000 hours, at most. Some of the amps with individual tube bias pots can be run colder or hotter, to get either (maybe) more tube life or more "class A" respectively. Don’t throw a blanket over a tube amp, but don’t bother with useless tube coolers either. You’d only need a fan if you’re sticking it in a cabinet. Don’t leave it on for a few hours just to save an on/off cycle. Just turn it on when you’re ready to listen. Unlike some SS amps, it should be at its best in 10 minutes. Any hifi amp you have today should be starting the tube heaters up well in advance of the high voltage, so it’s a safe start for the tubes. You would be hard pressed to find a tube amp anywhere that doesn’t have SOME mechanism for soft start. |
I always keep a back up set of the full tube complement for each amp. I’m also checking bias every time I run the units --using a Fluke meter-- after the units have fully warmed up using a digital source for the first 45 minute to an hour. I do run them at exactly the recommended setting which is printed on the top plate, next to each tube socket). I often check them at the end of a listening session, too. I used to never touch the tubes, using white cotton gloves to avoid any fingerprint oil, but abandoned that practice some years ago. Lamm recommends replacing the driver tube--a 6N6P--every two years for optimal performance. I don’t use the amps constantly. I do know someone--perhaps the oldest Lamm dealer-- who runs his constantly. I get fairly long life from the amp tubes, which I buy directly from Lamm since the 6C33C not only requires burn in (which Lamm does, not sure what the failure rate is) but also has a peculiarity in the output stage*--each 6C33C has a different range in which they properly bias and Lamm matches, by serial number, a tube suitable to the particular amp for that purpose. I thus never tried to buy the tube on the open market. (The particulars for this are not disclosed by Lamm but in talking with another tube amp engineer, he seemed to understand this-- it might be interesting to get somebody else who uses the tube, like Ralph @atmasphere to explain the technical details). Two are in each mono amp- one as the output tube, the other used for voltage regulation. (* I gather that the tube used for the power supply doesn’t require the same degree of matching but since I get them all from the manufacturer of the amp, I am not sure). One other thing I observed --the only tube I roll in the amps is the 12ax7 and have long preferred an old stock Tele ribbed plate (over the smooth plate). Many of the so-called NOS are, as you likely know, "pulls." I have been using truly never used old stock 12ax7s, a little more money but they seem to last much longer and the bias on the amps seems more stable. |
Cryogenic treatment-surprised it hasn't been mentioned earlier. Cryogenically Treated Tubes, the most cost-effective tweak for your audio system Of course, only for those who believe.
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@xenolith pretty sure your balanced power supply doesn't regulate voltage. Regenerators are the only power supplies I know that do. My amp has adjustable heater voltage. I do have to adjust it for different driver tubes but I'm using a wide variety of type 10,10Y, 210, 801, and 801A tubes. Jerry
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It is almost always better to turn gear off when not listening and turn it back on when resuming a listening session. Tubes are not light bulbs which are designed to come on instantly so they don’t suffer as much from thermal shock from being turned on. Still, a lot of tube amps do employ some sort of soft start circuit that ramps up slowly and/or heats up the cathode first before the full plate voltage is applied (to avoid “cathode stripping”). An amp with a tube rectifier can have the rectifier act as the soft start feature. The other practice to avoid is turning off an amp and then turning it back on again after a few seconds; the discharge from the caps can be damaging under these conditions. Wait a minute or two before turning the amp back on. Amps that don’t need the owner to adjust bias (cathode biased) tend to run tubes more gently. This setup does not allow the circuit to extract quite as much output from the tube, but the reward is often a longer life. |
Balanced power supply. It provides exactly 120 volts at exactly 60 Hz...constantly. IMO critically important to provide to tube amps...well, if you want your tube amp(s) to sound as it/they were designed to sound, which, sanity indicates you should. Oh, and bias holds better which increases tube performance and longevity,...huh, so I guess the more accurate sound is just a bonus to the longer tube life...funny how that works... |
