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tubes, ay caramba

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tubes, ay caramba

Postby Legrace » 18 May 2017 19:35

As I approach my first anniversary of tube ownership time to take stock. I would describe my current relationship with my monoblocks as somewhat love/hate. I just love the way tubes animate the music. The down side stems from all the things I've learned that can go wrong with tube machines.

I never knew there were so many ways tubes can fail. :shock: You got your red plate event, a runaway situation when the entire tube lights up like a roman candle. Or your flashover, when you get arcing due to a voltage imbalance. Then there's the gas out, when a tube loses vacuum followed by instant catastrophic failure. These are just the ones I've experienced so far, there are other failure modes as well. The red plate was the scariest. The amps main protection fuse may blow, or it may not. In my case it didn't. Which in turn can lead to collateral damage from the serious overheating associated with these events. I was lucky I noticed it before the damage was able to spread. Often losing one tube means I also have to replace its next door neighbor as well, sometimes even an entire quad. #-o :mrgreen:

While it may sound like it not trying to dissuade anyone thinking of getting into tubes. Tubes are like a cozy fireplace, a thoroughly enjoyable experience. SS now sounds sterile by comparison. The advice I would share is although they tend be more spendy, consider units with autobiasing/other sophisticated tube management circuits. Replacement tube costs can really add up so in the long haul things will even out. Plus you'll pop fewer grey hairs. :lol:

Despite the misadventures, I'm definitely hooked. System has never sounded so good. Only never turn your back on the suckers. [-X :lol:
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Re: tubes, ay caramba

Postby Legrace » 18 May 2017 20:54

Anyway, I was using the amp with my fairly new Sony Beta hi-fi deck to show some computer graphics stuff at my workplace on a projection system and the amp fried itself, which also fried my VCR.


Ouch, that definitely qualifies as collateral damage!
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Re: tubes, ay caramba

Postby rewfew » 18 May 2017 22:17

Hope I don't jinx myself, but I've only had one bad output tube, 16 per mono block over the 15 or so year span I've used a tube amp. It ran red, but no damage. It's a well engineered amp'(s). No one on the forum describes any catastrophic events happening. Tubes make the music move and your whole body groove.
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Re: tubes, ay caramba

Postby Legrace » 19 May 2017 12:43

rewfew wrote:Hope I don't jinx myself, but I've only had one bad output tube, 16 per mono block over the 15 or so year span I've used a tube amp. It ran red, but no damage. It's a well engineered amp'(s). No one on the forum describes any catastrophic events happening. Tubes make the music move and your whole body groove.


Had a gander at your gallery, what a unique amp design! I thought maybe you were talking the entire tube complement but nope, 16 x power tubes, per monoblock, holy crap! Internal design layout must be quite interesting. Managing biasing over that many tubes for example. What is the brand/model? Clearly the designer knew what they were doing, replacing just a single tube in 15 years is simply amazing. Thanks for showing us the other side of tube reliability. =D>

Not to mention your poetic take around the tube experience. :lol:
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Re: tubes, ay caramba

Postby theclosetguy » 19 May 2017 18:14

Legrace.
I'll say I'm sorry in advance. I'm not trying to pick on you. Again I'm sorry.
I have been using tube amps for close to 21 years. I started with 2- Dynaco St-70's, moved on to Dynaco MKIII's, a Mac 225, various Fisher's, Eico's, Heathkits and for the past 6 years I've settled on the PrimaLuna Prologue 6's. I have had power tubes wear out, I have had signal tubes wear out( that's what i get for using a "used" tube). The few instances where I have had catastrophic failure has always been my fault. While restoring a piece of vintage gear, I may have installed the wrong resistor value or crossed a wire. Buying used tubes, I might have a power tube with a broken guide pin and inserted it wrong in the socket, powered on and watched it glow.
I gave up using "Vintage" gear because it seemed like I spent more time rebuilding than enjoying. I had more maintenance issues than I wanted.
Your VTA M-25 amps are modern pieces of equipment based on a vintage design. I'm not sure if you bought them assembled or built the kits yourself but it sounds like you may have a cap or resistor or a combination that are not in spec.anymore. Power tubes need biasing occasionally as they age, but it is normally 100's of hours of use. Signal tubes last for thousands of hours.

Yes, tubes do fail. I have had used tubes go gassy. I'm a tube roller and changing out tubes constantly can lead to damaging pins and even breaking the glass loose from its base and shorting a tube out. I damaged 2 RTF El-34's dimple tops one day. But just like Rewfew, I have never had so many tubes fail in less than a year.
Again, I'm sorry if it feels like I'm being negative. Trying to help a fellow tube roller.
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Re: tubes, ay caramba

Postby Legrace » 19 May 2017 19:53

Not the least bit offended! You have been so helpful on other threads! The M125's are indeed fine units. Bought them as kits. I'd never built anything electronic before, didn't even own a DVM. Therein lies an important clue. :lol:

Failures were all rectifier tubes, except for one power tube that gassed out. The red plate event was also in a rectifier tube. So it finally donned on me, something must be going on with the rectifier socket, doh! #-o Examined it closely and noticed one of the pin connectors was projecting completely out of the socket! Anyway hammered down the wayward pin socket and as the same time reflowed a few suspicious solder joints. Since then all's been quiet on the western front. Newb alert!!

Bad connections can compromise an amp irregardless of type. Your reply serves to reinforce my advice about getting good tube gear, those Prima Lunas are sweet! I lusted after them but they proved a hard find in my neck of the woods.

I really enjoyed the DIY aspect but I guess my post is really a cautionary tale, carefully double check your work if you do decide to go the kits route!
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Re: tubes, ay caramba

Postby rewfew » 19 May 2017 20:40

Legrace wrote:Had a gander at your gallery, what a unique amp design! I thought maybe you were talking the entire tube complement but nope, 16 x power tubes, per monoblock, holy crap! Internal design layout must be quite interesting. Managing biasing over that many tubes for example. What is the brand/model? Clearly the designer knew what they were doing, replacing just a single tube in 15 years is simply amazing. Thanks for showing us the other side of tube reliability.

Hey Legrace. Yes, the man know's tube design. Probably more than any bloke on the planet concerning OTL amplifiers. No output transformer, just the tube's going to the speaker. Names Bruce Rozenblit of Transendent Sound. Biasing the tubes is easy and drift is minimal, I check it once a year. His mantra is reliability and simplicity. Using readily available non audiophile parts and unique circuitry, which is the key to his designs sounding so good. I use high sensitivity horn loaded speakers with the mono blocks for big high detail sound.
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Re: tubes, ay caramba

Postby Legrace » 19 May 2017 21:52

Thanks! Just visited the Transendent site, impressive gear!!
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Re: tubes, ay caramba

Postby Spinner45 » 19 May 2017 22:22

Tube equipment performance and reliability depends on multiple factors.
Good design, proper service, and reasonable operating procedures.
Meaning, operating the tubes within their rated specifications.
When this is observed, the equipment and tubes can last a lifetime.
I've seen tube equipment made in 1929 with "still good" tubes, as well as 1950s/1960s equipment with good tubes.
Of course, what is under the chassis is important too, if reliability is to be had.
Changing a failed tube isn't always the best cure - a new one can also be cooked in short order if that under-chassis stuff is in need of service.
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Re: tubes, ay caramba

Postby gofar99 » 20 May 2017 00:22

Hi, This is pretty much FYI and may not apply to your amps. (you didn't specify what the actual tubes were) I'm a long time tube user and have had zilch for problems. I have several tube amps of various sizes and none have given me any issues. However, recently (last year or two) there have been a significant number of problems with current production KT120 and KT150 Tungsol tubes in power amps. The tubes either fail nearly immediately or exhibit the various symptoms you mentioned. Folks are getting wary of tube amps for problems that are not inherent in their design. If yours were NOS ones this should not have occurred.
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Re: tubes, ay caramba

Postby Legrace » 20 May 2017 01:16

gofar99 wrote:Hi, This is pretty much FYI and may not apply to your amps. (you didn't specify what the actual tubes were) I'm a long time tube user and have had zilch for problems. I have several tube amps of various sizes and none have given me any issues. However, recently (last year or two) there have been a significant number of problems with current production KT120 and KT150 Tungsol tubes in power amps. The tubes either fail nearly immediately or exhibit the various symptoms you mentioned. Folks are getting wary of tube amps for problems that are not inherent in their design. If yours were NOS ones this should not have occurred.


Mostly 5AR4's. Since switching to NOS GZ37's stability has improved greatly. Power tube wise I just installed some KT120's, as I've read they are robust. Or are they? Arghh!!

BTW, please share detail of DIY custom Dual 701? Curious what aspect is custom...
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Re: tubes, ay caramba

Postby gofar99 » 20 May 2017 03:23

Hi, I hope your KT120s work better than the feedback I get from my UK dealer and another in Canada. The Dual had damaged parts in the automatic cam and components. Since the star of the player is its ESD1000 motor/platter I removed it and the control components (upgrading the speed control pots and switch at the time). I fabricated a wood sub chassis that acts like a case and a plinth for the actual motor assembly. They are separated by Isopods. Since the arm was not really usable I first went for an Origin Live Alliance one. Worked fine but I like to be able swap cartridges so I switched to a Jelco 370H. I used it instead of the 250/750 series as the mounting distance is the same as the OL (about 9.5 inches). The end result is a very heavy turntable that is quiet and plays well. I also went to and external 20VAC power source (one less source of nearby hum) and replaced the neons with LEDs that run off the 20VAC as it enters the motor assembly.

I went through several materials for the plinth and finally settled on a chris-cross laminated board designed for table tops. It is painted with stuff that looks like granite. The sub chassis is oak. I put adjustable feet (3) on the sub chassis to permit leveling. The blue pads under the feet are from a machine company for putting under equipment and give additional vibration control (I ordered more, but they have been out of stock for 6 months now). The turntable is on a very strong shelf attached to an exterior brick wall. Earth quakes might wiggle it, but not muck less would. The wire hanging off the side is from the altered dust buster. I just wanted the anti static features of a brush and the roller seemed to cause problems.

It all sounds difficult, but anyone with some woodworking skills and a bit of soldering and mechanical ability should not find it difficult.
701 May 2017b.jpg
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Re: tubes, ay caramba

Postby Legrace » 20 May 2017 11:41

:shock: Mostly I was expecting a custom base! Rare to see much in the way of mods to a Dual, why I was asking. I feel you are understating your abilities. I have no doubt it sounds lovely! I agree that while Duals are generally regarded as capable mid range tables the ESD motor is as good as they come. Using it as underpinning for a high end performer makes perfect sense. The specs on that motor are superb. Thanks for taking the time to share details of your highly original custom Dual.

Re the KT120's only time will tell. The power tube that failed was a KT88, after only a few weeks when the glass cracked. So had to decide, replace or change up. So now I have one monoblock with KT120's and the other is still running KT88's. Not ideal, but no way I'm shelling out for anymore tubes for the foreseeable future, budget's blown. :cry:
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Re: tubes, ay caramba

Postby kb007 » 20 May 2017 12:51

It's funny to hear younger folks react when you tell them you use tubes...

I've been a tube guy for most of my life, built my own 6L6 based power amp back in the late 70's. All my guitar amps are tubes (Fender and Marshall), never played a SS guitar amp I liked.

My audio tube gear started with an ST-70 many years ago. Cleaned it up, replaced the selenium rectifier and a few caps and it sung well. Had an Audio Research tube integrated for a while. Found a pair of Mk 3's that had ben 80% restored (re-capped, new chrome on the chassis, xformers painted and other goodies), I finished the job and they looked stunning. I happened to be talking to a guy in my local shop one day about them, it turned out he was the guy who did the 80% and then sold them to the guy I bought them from. He immediately asked me to buy them back and made me a great offer. I didn't have the heart to keep them, so I sold them back to him. They ran well, but didn't really work well with the Totem Arros I had at the time.

My current audio system amp is an AR VT-100, which is built like a tank and sounds awesome.

In all that time, I have never had a tube go bad on it's own. I've had very old amps pop their caps on startup (I didn't use a variac to bring them up), but never actually has a tube go bad. Maybe I'm hugely lucky (can't tell you how many times I've rolled 12 ax/at/7025s in and out of guitar amps.

BTW Legrace, I like what you're doing with SS for low and tubes for hf. I was considering something like that for my video system, but was a little concerned about the on/off cycles of the everyday use of the video system, which is why I went SS. Hmm, now you got me thinking about maybe swapping out the main channel amps for something with bottles...

Tubes are generally very reliable, I'm a little surprised you had KT88's crack - what brand was it?
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Re: tubes, ay caramba

Postby Legrace » 20 May 2017 16:04

You guys and your rock solid gear, must be nice to live like this guy :bored:

Tubes are generally very reliable, I'm a little surprised you had KT88's crack - what brand was it?


From what I've read the defect rate trends higher in modern tubes. A quick search can turn up complaints re short life/multiple failures across virtually all brands. On the other hand I have yet to lose any of my older NOS style tubes. Now only if they weren't so pricey. #-o
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