3-500 Tube Life

 Saying that I made up the statement in Section 6.11, Tube Life, in Eimac's "Care and Feeding of Power Grid Tubes" is what else Susan?

 I am not the someone who is trying to propagate a hoax on this thread.
• Rich, ag6k

 

So you couldn't estimate how much time is spent on the air by the average ham every year?

This has everything to do with the lifespan of tubes used in amateur amplifiers.
One cannot make any valid statements about tube life, any tube used in amateur service without taking into account the behavior of the end user. Tube life is meaningless when it's couched in static terms, the type of service, power cycling (and temperature cycling associated with power up and shut down) all figure into the lifetime of any electronic component. The claim that reducing filament voltage in power grid tubes to a point will increase lifespan is valid, but at what cost and and how difficult is this going to be for the average ham to carry out?

I still find it hard to believe that Eimac or any other transmitting tube manufacturer didn't or doesn't have life expectancy data. Even RF Parts will warrant their tubes for a period of time, so even they have an idea of how long the tubes they sell last.

What I am driving at is if a given transmitting tube has a design lifetime of 20,000 (2.28 years) hours of continuous broadcast operation as a class C power amplifier that translates into more than twenty years of weekend operation. With all the thermal cycling the likelihood of a maniacal or seal failure becomes a real concern when that tube is more than fifteen years old.

Now ask yourself; Is it really worth all the trouble closely monitor filament voltage and invest in the time and expense just to get on the radio for a dozen hours every weekend?
Even at twelve hours a week, that would be over thirty two years of operation. What would be the point in doubling that??? The tube in question is likely to fail from repeated thermal cycling by the twenty year mark.

 

I don't see anybody saying you made up statements regarding tube life VS filament voltage.
I could be wrong, but I have been following this thread since it was started.

I know you are not trying to propagate a hoax, I am challenging the validity of riding the filament voltage (my words) on tubes used in amateur service.

 

Anyone can estimate their hours. For example, I used to operate pretty heavily, about 3-4 hours a day, and always ran the amp. During that time I would cycle my amp off for full power down just twice.

My operation, which was more than anyone I knew, was about 1250 hours a year, with over 700 full cool down cycles. That's ten years to get 12,500 hours.

Without voltage regulating filament voltage, Eimac says use the nominal voltage as a mid-target.

A ceramic-metal broadcast tube is typically operated at 10-30% of full ratings. A glass tube, with gettering on the anode, has to held at about 30-50% to stay gettered.

All of them have far more airflow than any Ham would ever tolerate, very rarely cycle with temperature, and virtually never get mistuned or overheated.

This alone, not counting hours, is far different than amateur use.

History of failures speaks for itself. Most higher quality manufactured amateur tubes fail from overheating abuse, gas, or mechanical failures unrelated to operator control, like bad welds that let go from thermal cycling. Some are common manufacturing defects, for example about 60-70% of Amperex 3-500ZG tubes from Richardson's failed within weeks of initial use date from grid filament shorts.

Chinese tubes have two issues, grossly premature loss of emission and gas failures. I have a pair of RF Parts 3-500ZG here, pulled from an amp that had all of Rich's mods, including filament wire size, that failed within two years of initial use. That operator told me he ran the tubes about 1-2 hours a day.

On the other hand, a friend has a DTR2000 which is well known for running the 8877 1-1.3 volts over the 5 volt rating, and still has an original tube from the mid or late 1970's!

It's just silly to think or claim someone is going to noticeably change life by reducing voltage.

73 Tom

 

It just doesn't make any sense to me to go to the additional expence and trouble when there are so many other possible failure causes that likely to crop up before the filament has lost it's ability to emit electrons.

Oh and for anybody who is interested The Care & Feeding of Power Grid Tubes is available on line at the Eimac / CPI website.
http://www.coutant.org/eimac/index.html

 

 If you had been using an unmodified Henry 1KD-5 Tom you would have gone through c. 9, 3-500Zs per year.

 "My Care and Feeding of Power Grid Tubes" says nothing about a need for a regulated filament PS. Why would one be needed if low filament-V does not cause permanent damage?

 Assuming that all tubes have leaky seals.

 RE: 3-400Z and 3-500Zs: IME, bent-filament touching the grid cage is/was often accompanied by:
1. big bang.
2. damaged or blown parasitic-suppressor R.
3. zapped grid RFC in L4-Bs, Tl-922s, and SB-220s
4. no arc mark subsequently found during tube autopsy.

 When an oxide-cathode tube like the 8877 is run with excessive heater-V, the extra heat causes barium oxide to migrate from the cathode to the grid. However,the 8877 does not fail.

 Then "Care and Feeding... ..." and Econco Broadcast Services are silly.
• Rich, ag6k

 

 The supposed necessity for riding the filament voltage 24/7 was an artifice used by the opposition. I have not measured the filament-V in my SB-220 amplifier in years because the HV is virtually unchanged. . . . . Excessive filament potential is more of a problem with some amplifiers than others. The Heath SB-220 is one of the better engineered amps since not only does it have a current-limiting type filament-xfmr to address the 29A-max filament inrush spec, the filament potential is typically on the low side so it does not waste emission from the get-go. . . . The emission wasters are the 1KD-5, the 2KD-5, the TL-922, the Loudenboomer, the Tokyo High-Power 3-500Z amp, and a few others.

cheers Susan
• Rich, ag6k

 

 For the owner of a Henry 1KD-5 or 2KD-5, the cost of changing the filament circuit to smaller gauge TFE wire to reduce filament-V would net considerable $$. Other problems with Henry KD amplifiers are the use of a high VHF-Q parasitic oscillation suppressors, no step-start/soft-start, no +HV glitch-R to prevent filament-grid shorts during parasitic osc., no meter movement protection, and a filter-C support board that absorbs moisture from the atmosphere.

 Hmmmm , , Maniacal Failure - now there's an interesting one Sue.

 The only thermal failure I know of was metal-anode 3-500Zs that Eimac mfg in Salt Lake City.

Rich, ag6k

 

Anecdotal: I had a Henry 2KD-5 from 1976 to 1988 and used it a lot including several M/M contests. In '88 when I sold it, it still had its original Eimac tubes and they still ran the same power as they did 12 years earlier, in '76. It probably had 6000 hours or so of transmitting time by then, and nothing changed over the 12 years.

That was one of the amps at our K2XR contest station in NJ/NY and must have been used in at least 20 contests, where it was transmitting half the time.

I must admit, I never measured the filament voltage. I only learned years after selling it that it was probably too high!

But it was a solid amp, for a small desktop.

My "fave" Henry amp was the 4K Ultra, which I also owned for years, and it actually DID have a filament voltage control system and meter for that. I don't recall ever adjusting it, but it had the capability (that was an 8877, quite a different tube from 3-500Zs). I miss the 4K Ultra, it was pretty slick but didn't cover 160 meters, which is why I sold it. Well that, and the fact that it weighed 192 lbs and occupied a lot of floor space.

 

Rich, ag6k I am starting to become confused if you can build the nearly perfect amplifier then why are you not doing it? By the look's of the cost of high end amp's it appears folk's are willing to pay to have them.