tube reliability

[chopchip]

i have been looking for a thread where tube reliability is discussed, what people's experience is with tube life expectancy vs final age of passing.

i have read a faq at vacuum tube.com regarding the state of tube manufacture these days it seems that the golden age of tube manufacture has passed and that we will never see those days again when tubes were pumped for 2 0r 3 hours and when ultra-pure cathode materials were used.

"... they are not recreating the complex cathode formulae using super-expensive reagent-grade chemicals, expensive metal alloys and metallurgy and quality control that
were prevalent up until the early 1970s in those factories"


a few eye opening quotes from this FAQ



"We have estimated that as many as 40% of the "NOS" audio tubes being sold on eBay are outright phonies."

"Rebranding is as old as the vacuum tube itself. In the 1950s, there were enormous problems with dishonest dealers taking used or factory-rejected TV and radio tubes, cleaning them up externally, and
offering them for sale at cut-rate prices in magazine ads."


"The only way to avoid being ripped off is not to participate."

" NOS RCA 6L6GC Blackplates, once a $20 tube, now sell for up to $175 each."

i am curious to know what the experienced people in this forum have to say on the matter. i recall a short discussion in another thread where someone had a "secret tube" that was good for audio amplification but was as yet undiscovered and whose price had not inflated astronomically.

[smoking-amp]

I just use TV tubes, no "audio" tubes. Can get 17 Watt sweep tubes for a $1 and high performance frame grid video tubes locally for $0.50 in quantity. Just buy enough to keep your amp design working for the next century (less than the price of one "audio" tube) , and don't go blabbing publicly about how wonderful such and such tube sounds. Or you won't be getting any more of them cheaply.

[richwalters]

I'm open on this one. However, the Ebay outlet, is well known for tubes of all types and conditions appearing, the financial crisis pushing many the pluck into the heap of semi duds.

There is the classic test of how good the tube vacuum is by measuring the reverse grid1 current.......manufacturers can't get away from this test. A well made KT88 should exhibit less than 1uA at quote currents and voltages. Some were considerably higher.

However, the possibility of roapy dodgy tubes which was rife in the 1970's has been always around. Car boot sales ? It's ones pick and a risk..one can get a bargin and a good runner.. Where I worked, many used tubes on the TV shelf were workable and up to spec, perhaps rejected with a rough figure on heater to cathode insulation, or markings obliterated. Many were resold as "ex equipment", untraceable, no guarantee.
Those of us who tried the early Shugang power types that appeared in the West during in the late 1980's were often horrified how short a life they had. They were known to be very poorly made with no Quality control. The Chinese have excellent quality fireworks, so QC has definitely changed.

[Lingwendil]

I've found that many times the best way to get good audio tubes is either go US and Soviet surplus, or find old tubes locally. Protip- check hospice, antique stores... I've gotten half a dozen NOS 300B's for three bucks a piece this way! Same for 12SN7, I've gotten them for a buck new.

[el156]

Hi !
I am only using NOS tubes that i have been collecting for a long time . I am still using tubes i have for 30 years,and still working perfect ,like ECC81 ,82,83 most from Philips and Telefunken (and EF86). But very soon i need to buy some new EL84 and i dond know wich make to buy,but i know for sure i will not buy chineese tubes. Maybe you can advise me for the best ones!
Thanks

[BadassBob]

In hifi equipment, tubes can live a very long life. If youre a guitar player, you might want to amass a large quantity, because their life shortens exponentially when you overdrive em.

[chopchip]

Originally Posted by BadassBob

In hifi equipment, tubes can live a very long life. If youre a guitar player, you might want to amass a large quantity, because their life shortens exponentially when you overdrive em.

a jj el34 just went on the fritz after about 50 hrs and it should have lasted about 3000. i have been through several gz34s too so im a bit leery here and i have gone SS. the 13em7s in the miniblok2 give me a sense of security knowing that they are still only 5 dollars a piece NOS but my st70 has been giving me anxiety ever since i got it. there are a number of power tubes that can be run in the st70 but they are no cheaper than the el34.

i have to get my voltages down and run the thing a bit cool maybe then i will be able to listen to it without a sweat breaking out on my brow

[Miles Prower]

Originally Posted by chopchip

Rebranding is as old as the vacuum tube itself. In the 1950s, there were enormous problems with dishonest dealers taking used or factory-rejected TV and radio tubes, cleaning them up externally, and
offering them for sale at cut-rate prices in magazine ads."

That's what Rat Shack did with their Realistic Lifetime line of VTs: factory seconds. I had a couple of Realistic 6BQ6GTBs that had obviously been over heated during pump down, causing the glass to suck in a bit. Also, a Lifetime 5U4GB with a frosty getter, caused by premature getter flash.

Doesn't mean they don't work, although the "Lifetime" moniker is a bit of a hype, I'm sure.

As for failures, I had just one: a gassy 807. For VT types, I've used mainly Sovtek and NOS. The Sovtek's have been working just fine for five years now. No other problems with NOS finals and small signal types.

[Bobby Dipole]

Originally Posted by el156

Hi !
I am only using NOS tubes that i have been collecting for a long time . I am still using tubes i have for 30 years,and still working perfect ,like ECC81 ,82,83 most from Philips and Telefunken (and EF86). But very soon i need to buy some new EL84 and i dond know wich make to buy,but i know for sure i will not buy chineese tubes. Maybe you can advise me for the best ones!
Thanks

Hi El156, I just bought a new pair of JJ EL84s that are working out very well. The idle current matches the data in the spec sheet exactly. I have a half dozen NOS EL84s that all run too much current in my amp (a few even glow red ). My amp has fixed un-adjustable bias.

JJ tubes are made in the Slovak Republic.

Bobby Dipole