Tube Life in Triode or Tetrode

The maximum screen voltage and dissipation are specified in the tube data sheets. You respect these limits and the tube will have the same life. With Ultralinear connections and tying the screen to the plate for triode, people often will exceed the screen ratings and some say this is perfectly OK.

As long as you run the tube at 80% or less of max dissipation ratings the tube will have long life from an emissions standpoint. Most tubes fail from the heater/filament, however, by running the voltage to high and having a harsh turn-on surge.

RE: Tube Life in Triode or Tetrode , posted on August 6, 2020 at 15:55:08

trobbins
Audiophile

Posts: 189
Location: Melbourne
Joined: March 26, 2012

Two comments are not supported by statistical evidence -
'most tubes fail from the heater/filament'
'having a harsh turn-on surge'

Those comments are just isolated heresay.

That's not to say that an amp shouldn't be checked to confirm that the operating heater voltage is not high (for some reason), and then something done about it.

The link to harsh turn-on surge is often from people looking for a solution, when there is no problem, and happily highlighting their efforts to include delayed or soft turn-on operation of some kind or other (and mainly because they had seen or heard about someone else doing it).

Uhhhh Really?, posted on August 6, 2020 at 17:48:13
Chip647 Audiophile Posts: 2652 Location: The South Joined: December 24, 2012	Go ahead and run your 6.3v heaters at 7 volts and let me know how that goes for you. Soft start of heater/filament supply stops a large current surge on cold heater/filament wires, these are very hard on them and they do shorten tube life. Violating the heater/cathode rating is a fast way to the garbage too. Isolated hearsay? Really? lord.

RE: Uhhhh Really?, posted on August 6, 2020 at 19:35:42

trobbins
Audiophile

Posts: 189
Location: Melbourne
Joined: March 26, 2012

You made the comment 'most tubes fail from the heater/filament'. I'd suggest that is your view, but not backed by any rigorous statistics or testing or other reviewed form of assessment. You may have noticed that 'many' or 'most' have failed that way, but it does not make it a blanket truth.

And you then made an additional comment that heater/filament failures are related to 'having a harsh turn-on surge'. I'd suggest that is also not backed by any rigorous reviewed form of assessment or testing.

I've looked for any related testing/assessment, and very little was presented in the 1940-60 heydays, or after.

I didn't say that operating a heater above its rating would not lead to early failure, so you have misread my response.

A typical turn-on current for a heater/filament certainly does cause a large initial current surge of circa 3-5x the nominal level. But that has not been statistically shown to shorten tube life.

What has heater/cathode (voltage) rating got to do with this topic?

RE: Tube Life in Triode or Tetrode , posted on August 6, 2020 at 20:00:38
hahax@verizon.net Audiophile Posts: 4310 Location: New Jersey Joined: March 22, 2006	Tube life is strongly affected by the amp design. It depends on how good the designer is. David Berning's amps are designed for 10,000 hour tube life but actually will do much better. The audionics BA150 prototype, designed in the 70s was left on for 5 years with no measurable tube wear.

RE: Uhhhh Really?, posted on August 7, 2020 at 02:58:30
Lee of Omaha Dealer Posts: 1800 Location: Omaha NE Joined: September 8, 2006	We've tested at least thousands of tubes over the years. During that time we've seen 3 heater failures. Oddly, two of them were 12AX4 rectifiers. Tubes usually wear out, suffer shorts (most commonly heater to cathode), or get gassy.

What has heater/cathode (voltage) rating got to do with this topic?, posted on August 8, 2020 at 16:20:49
Chip647 Audiophile Posts: 2652 Location: The South Joined: December 24, 2012	Violating ratings makes tubes fail. Heater failures are common. Don't know what to tell you about your web search. I don't feel the need to do it for you.

RE: What has heater/cathode (voltage) rating got to do with this topic?, posted on August 8, 2020 at 18:38:04

trobbins
Audiophile

Posts: 189
Location: Melbourne
Joined: March 26, 2012

Just clarifying that turning on an amplifier, where each tube experiences a normal heater surge current whilst the heater/filament is heating up, is not in any way violating a tube rating.

I've been lucky enough to search a lot of the technical/scientific literature, but there is always something new coming out of woodwork every now and then as more vintage documents get scanned. The closest technical assessment I've seen so far relates to a large early valve computer, and the measures they took to improve reliability of that equipment.

RE: What has heater/cathode (voltage) rating got to do with this topic?, posted on August 9, 2020 at 06:53:32

Chip647
Audiophile

Posts: 2652
Location: The South
Joined: December 24, 2012

The tread is on a primary failure mode of tubes, and I would add particularly susceptibility of new manufacture Communist bloc tubes, being heater/filament failure.

Over-voltage is one way to open a heater, another is a high number on/off cycles versus hours used, as well as violating ratings like heater to cathode voltage ratings.

Obviously there are other failure modes, but to say that I am just regurgitating garbage on heater failure being common is rather insulting.

Wrong question, posted on August 11, 2020 at 05:41:08
Cpwill Audiophile Posts: 1096 Location: DC Joined: December 22, 2003 Contributor Since: October 24, 2008	Why worry about tube life? Unless you have some spendy NOS unobtainum tubes, the question is: Which sounds better. "Anyone who understands jazz knows that you can't understand it. It's too complicated. That's what's so simple about it." - Yogi Berra. Cpwill

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Tube Life in Triode or Tetrode

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