Tube Longevity

Hi, under NOMINAL conditions (1.56v bias, 117v power) approximately how many hours will a typical output tube last in an ST70? Does playing at high volumes reduce tube life more so then just on but idling? I assume a tube fails when it "runs out" of electrons on its cathode or its filament burns out so it's probably not good to leave the amp on if it is not being used. Thanks!

General consensus is the average power tube should be good for around 3000 hours, all else for 10,000 hours. As you mentioned, how hard you drive them can make a big difference. That was part of why I went with the KT120's in my ST120 - I figure they should last forever in a KT88 based amp.

(Not an option in the ST70 btw ... not enough iron to keep them happy)

I turn mine off if it's gonna be a couple or three hours between sessions or when I leave the house.

sKiZo wrote:General consensus is the average power tube should be good for around 3000 hours, all else for 10,000 hours. As you mentioned, how hard you drive them can make a big difference. That was part of why I went with the KT120's in my ST120 - I figure they should last forever in a KT88 based amp.

(Not an option in the ST70 btw ... not enough iron to keep them happy)

I turn mine off if it's gonna be a couple or three hours between sessions or when I leave the house.

I've resolved bit of the tube-ageing issue by installing some Bedini sand amps when I just want background music to listen to while I'm working, to save wear and tear on the tube rack. (Am also running Tung-Sol KT-120s).
Bias setting also has an influence on tube life. If you can live with say, .5 or .55 per tube, your tubes will live longer, or so I'm told. Andy Bowman suggests as low as .45 as a starting point for KT-88/6550 tubes.

Bob L, Roy, you guys might answer this one: does running in triode mode have any salutary effect on tube life?

Way I understand it, a tube in triode mode runs just as hard, if not harder, as a pentode configuration. Difference in output is due to how the signal is routed through the tube.

And ya ... stands to reason that a lower bias setting will go easier on the tube, but there's always a trade off. I prefer the PUNCH of a higher bias. Especially true with the KT120's as those really sing at 60mV ... maybe more so in a KT88 based amp. Much of the "sound" is due to how the tubes interact with the rest of the components in an amp, and my target is the "sweet spot". Given that, or improved longevity ... hey, you only live twice ... ;-}

PS ... I seldom "listen" to music. For me, it's more LISTENing when I have the time to sit back and sink in. Full immersion, doncha know ... blub blub ...

According to an old Sylvania engineer, tubes should last roughly 10,000 hours. Power tubes can achieve this by running at half of max dissipation. Now there's a puzzle for you to solve.

corndog71 wrote:According to an old Sylvania engineer, tubes should last roughly 10,000 hours.  Power tubes can achieve this by running at half of max dissipation.  Now there's a puzzle for you to solve.

There's plenty of anecdotal evidence that the 1960s-vintage production tubes lasted that long. Guess the modern solution would be an M-125 running eight KT-120s.

And sKiZo, I'm kinda with you. Life is short, tubes are cheap. I run mine at .6.

I run my Shuguang EL34s a little high at .425v; they sound more dynamic that way. At less than $40/quad, I'm not too worried about tube life. Heck, at 70 years old, I'm more worried about Gregg's longevity!!

Have a Happy New Year!!

Good Point! Life is short, turn it up!

n3ikq wrote:Good Point! Life is short, turn it up!

November 3 and sKiZo, I'm with you guys. We can always get new neighbours.

I went through a lot of neighbors until the deaf guy bought the house next door.

He still goes on about the "ghost trains" rumbling by and shaking the house at odd times of the day and night. I'll see him through the window, out in the yard and looking up and down the abandoned track bed trying to spot one when I'm cranking it ...

Get him a "bass shaker" for his easy chair......

Bone conduction. We need bone conduction . . .

Yeah, what Bob said. Pass that thang over to me so no more drifting.

audiobill wrote:Get him a "bass shaker" for his easy chair......

Speak of the devil ... Looky what I did to my easy chair just last week ...




Driving them with a 200wpc mono plate amp ...

Trrrrrrrryyyyyyyyy iiiiiiiiiittttttttttt
yyyyyyyyouuuuuuuuuuuuullllll llllllllliiiiiikkkkkkkkeeee iiiiiitttttttttt!!!!!!!!!!!

EDIT > > Just caught the admonishment about thread drift ... er ... uh ... these will definitely shorten tube life unless you isolate the amp. I use Vibrapods -



Stacked #4 and #1 under the back corners where all the weight is, and single #1's on the front corners. Zero vibration transmitted from the room. Highly recommended!

There ... back on track ... sort of ...  

SkIzo, I am really tempted to try one of those b*tt-shaker layups, just 200 more watts not on the financial table right now.
There was an article maybe 30 years ago in Stereo Review (or was it Mad Magazine) about direct bone-conduction bass, written tongue in cheek, before the era of megawatt amplifiers or the invention of powered or even passive subwoofers. Can't remember where the needles went.
If an OCD tube-roller, be aware of pin dimensions, as Bob L. just mentioned. They DO vary. Antique Tung-Sol 6550s have smaller pins than their new Russian KT-88/120 counterparts. If you've been using Russkies and then try out a set of original 6550s, you'll find much to your discomfort that the Russian pins have blown out the pin-holders a tiny bit, to where the old tube will not make contact at certain, important places like Pin 7. It's a pretty light show when that happens as your beautiful antique 6550 red-plates and emits magic smoke, but it's not worth the hundred bucks.
Quick fix: tighten up the sockets with an optical screw-driver, pour a bucket of D-eoxit over the mess, squirrel in pipe cleaners to muck 'em out, and wipe the tube pins with some bronze wool. Repeat.

My hard-earned advice: suck it up and buy the best New Jersey or Dutch tubes you can, especially for drivers and preamps. Second-best advice: the Russian Tung-Sol KT-120s from Jim McShane are pretty tough to beat and you can drive the shite out of them. If they go to the grave at 3k hours, that's in the real world probably three to four years. Not a bad thing; they'll make more unless we go to war. Consider them meantime as consumables, like hamburger.

Last thing, has anybody seen MontanaWay's (Holger's) new Big Bopper M-125s on tube nirvana? Individual per-tube bias, and a board that replaces the multi-cap with individual caps, all mil-spec PCBs below decks. Holger works in concert with Roy and Bob so all is kosher.

I have a quad of JJ-6550 in an vta-70 that has been active since june 2013.
Since november 2014 they have accumulated 160h so my guess is that they have done >2000h
Still no bias drift and no flashes.

Bass shakers - constipation cure!

More on topic, more or less.

I did pick up an hour meter for the ST120.



Truth be told, I really can't say how many hours I've accumulated, and that should take the guesswork out of it. This one has non-volatile memory, so it doesn't lose the hours. Plenty of places I could pull DC from the chassis, but ... I've been planning to install a 24v power supply to do some lighting, and that's yet another reason to git er done.

Rectangle LCD hour meter quartz 9-80 VDC, hourmeter

---

bASS shakers are something I was looking into for a while now. The ST120 paired with the Big Mac speakers can certainly get the rumble going, but these are pretty amazing. Yet another level of immersion. I did get a bit carried away with the amp ... 100watts should be more than enough to drive a pair hooked up in series to deliver a four ohm load to the plate amp. As is, I can only turn them up about a quarter of the way before I endanger the foundation here. Have to play around with attenuating the line level to see if that helps.

And bone conduction ... I still got my bone fones ... anyone remember those?



Just toss them around your neck and adjust the transducers to hit your collar bones, and instant stereo. Pretty slick - I still use them when mowing the lawn.

$80 was a lot of money back then. Gas was what ... 70¢ a gallon?

Luck with finding them on da bay, eh. Not sure if they didn't last, or they didn't make many, or just that folk who have them tend to hold on. Mine have held up well over the years, but I don't treat them rough either. You gotta wear the strap to get good conduction, or a sweatshirt works fine to keep the transducers tight to da bone ... good sound, and I get good reception out here in the sticks too ...

Oh ... tube longevity. The blue tube that covers the radio has held up well as well ...  

I'm sure this horse is almost dead, due to the repeated beatings----However....   I own and use a rebuilt (by me)ST-70, a PAS-3x, FM-3, Scott 299(a), 3 Heath A-9(C)'s, 2 Heath AA=121's, 1 Heath SA-2, 1 Magnavox AA-175, 2 Baldwin 54A's, and even a Silvertone Console Amp (PP-EL-84 X 4).  Also own a Jolida BRC-302, since I had to have remote in one of 'em.    In 12 years of engaging this addiction, I have only burned up a few power tubes-- (EL-34's in the Heath Amps).  This is attributed to two things: 1)  I always put in a CL-90 (or whatever appropriate for the device) Inrush Current Limiter in the Primary Circuit, and 2).  Never go beyond 115 VAC.  By necessity, this requires a Variac during all listening.  I have found no adverse effects from using this method, other than a slight increase in hum.  My K-Horns hum with everything, though--so it's really no big deal.  I'm sure there is a downside to this method, but it has worked for my equipment.  I don't want to ruin the vintage tubes/transformers I have, and this is the only way I have found to preserve them.  On occasion, I do crank some of these amps with KEF Reference 107/2's---These are 4-Ohm (more like 1 ohm at some frequencies) Power Suckers.  This, just in case some might think my amps are never "stressed."
Can't wait for some of you to weigh in on this one!
     

Varaics...I have 8ea here today....get them at yard sales...fleas....$10-15 at most.
Never lose tubes... having  tubes for over 40years....just don't kill tubes!.. an all my Vintage tube amps an pramps Never sounded better with the AC set at 110-15....I sale a tube amps from time too time....thay get a Varaic with the Sale!..........
I got tube here that are over 50 years old.....test 80-90%.....with the price of tubes...  think others would get this ezey fix....but there just post after post about tube death on all sites ....

An how about the sound of the old hhscott....299c..355 pretuner puts my Krell KBL&KSL to shame...hehe ... some of the best tube sound I have ever had...
An scott run some of there input  tube heater at 5.70.....
But never used any cl-90s....but I sound like a plane...
Thanks for any an all info on tubes............



Thanks for the site Bob.......