Tube life expectancy

[KE6DF]

It's interesting to me that some tubes have a reputation for short life and others seem to never wear out.

For example, 6146's are generally considered a short life tube that needs replacing every so often.

Sweep tubes have the same reputation.

But 813s and 4D32s are generally assumed to last for decades.

But, is there really a difference?

Did 6146's get a short life reputation because early Vikings etc. pushed them too hard and burned them out prematurely -- in an effort to get maximum power?

Same with Sweeps being used in low end linear amps?

Or are 6146s and Sweeps and a few others like 6V6s really designed for shorter life?

[W2PFY]

Those other types like 6146's will last decades too if they are run conservatively. Too often smaller tubes are run at ICAS ratings and they fail. Another thing to consider is the cathode of smaller tubes. Assuming proper filament is applied, these tubes may have different life spans depending on the manufacture. The cathode and all the materials and experiences by the manufacture determine the life of a tube. So a GE for example may last longer than a Westinghouse depending on who has the better cathode.

There are 8760 hours in a year. If we operated a rig for ham use for three hours a day the tube would be used 1095 hours in a year so you can see that the tube would probably last decades because very few of us operate a transmitter 3 hours a day yearly. Some tubes have a design life of 5000 hours and that suggests they would go longer.

In broadcast the larger tubes often will go well beyond 10000 hours but most will be at less than full specifications after 1 1/2 years. that is not to say they won't go for thousands of more hours at reduced output. At the end of the day, it depends who you are talking to when it comes to tube life. Many have no real experience on the subject and are depending on hearsay for their information.

[Jim, W5JO]

I haven't had your experience with 6146s or 6V6s.  The DX 100 ran  two 6146s at much higher dissipation (ICAS voltage)  than Johnson did and I rarely saw problems.  Johnson used three and ran them at a lower (CCS) voltage.  The only times I have had problems is when you run tubes in AB, AB1, AB 2 or class B to do SSB.  Since the duration of speech is so short, manufacturers always pushed tubes to their limits for that mode.

Manufacturers limits and operator limits are much different, so most of the time the operator causes the problem.  Same is true of sweep tubes.

[WD8BIL]

Operator habits play a substantial role. I had an HW101 (6146s) for 15 years and never replaced the finals. Still did rated output when I sold it. Again, my Viking 2 went 6 years with no final failures.

We all know guys who have Viking 2s that eat finals at a good clip. My guess is, they're operating tendencies are toxic to thesse tubes.

Admittedly, this is anecdotal but I haven't seen the 6146 short life tube reputation played out in my stuff.
 
Even the 6146s in my GE proglines lasted years at 6 and 2 meters RTTY!

[w3jn]

It's always better if you don't beat the snot out of them to derive every last watt.  Of course you can do that and more with an 813 and it never seems to bother 'em.

When in doubt follow TMC's philosphy and run 'em conservatively... like the 6146 running 2 watts in Class A in their SSB exciters.  Longer life, less splatter, everyone mo' happier.

[The Slab Bacon]

My SX-28 still has the original 6V6s in it.

my 4X1 rig still has the same 6146 driver in it that I used when I built it 10 years ago. And it was used when I installed it! It runs class C with 500v @ around 90-100mils which is close to what a viker 2 runs on its finals. (50w input each) The 4X1 was used when I built the rig and has yet to lose any emission to speak of. (It came out of a shaker table) I did have a filament failure in one of the 5933s, but that is the only tube related failure that I have had with it, and that rig has gazoodles of hours on it.

Like others have said, it is more the operator (or circuit designer) than the tube.

Actually, In all of the stuff that I have either built or repaired, tube problems have been extremely minimal. Many times ones that show weak or questionable on a tube tester still work OK-FINE in the circuit. The tube checker is usually the last piece of test equipment that I reach for when troubleshooting a piece of equipment. Excessively weak tubes will usually show up in the in-circuit voltage checks. Then a tube checker just confirms the diagnosis.

[Opcom]

It does not take more than a few accidents such as severe over-current for a short time or a few minutes of no bias with a cherry red plate to pretty much ruin a tube, especially small tubes like the 6L6 and 6146.

I've seen sweep tubes in color TVs that have run for years with a dull red spot. I sort of miss working on the big old color TVs with 35 tubes and all the delta gun convergence stuff, 6BK4 regulator, etc. The larger sweep tubes have much bigger cathodes for the equivalent plate dissipation rating and thus very high cathode current ratings for the size, and the TV running it in class C is not abusing the thing as much as in ham service, which may have something to do with it.

[KM1H]

Too much grid current will kill a 6146 in a nanosecond. Another big problem with the Viking II is that owners use that roller tank to try to load into anything and with no screen current monitoring or safety trip the current soars and they are toast.

The 6146 seems to enjoy a long life in S Line and Kenwood hybrids. Kenwood has a fan on them.

I used to go thru a pair of 6JB6's every 3-4 months in my T4-XC's until I added muffin fans over the cages. Since I was actively DXing and contesting there was no way to minimize tuneups, I was all over the bands in both modes. With the fans I had no more failures for the remaining 2 + years untill I went SS for a coupla TS-930's.

[K5IIA]

I would bet that tube life is more based on the operator, and his idea of acceptable operation.

[K1JJ]

I used to go thru a pair of 6JB6's every 3-4 months in my T4-XC's until I added muffin fans over the cages.

AMEN Brother!   Can I get a witness?!!  Pass the basket!


Cooling is the key. The common thread with power tubes is heat. Same for solid state stuff - heat will shorten life.

Excessive heat on power tubes will cause the seals to deteriorate over time and slowly let in air contaminates. The vacuum is compromised.  The tubes start glowing blue -  and are soon history.

I lost a few really nice external anode tubes in homebrew linear service by having too little air on the seals. They started to show discoloration before I figgered out what was going on. Stupid mistakes. The bottom area where the pins come out is important to keep cooled on external anode tubes - and the plate cap and bottom pins are critical areas for glass tubes.  Blow air on these areas for maximum life.  A good socket and chimney design will do this automatically if the air flow is adequate.   Smaller glass tubes are less demanding, but it doesn't hurt.

Keep a tube happy with plenty of air and keep currents and voltages within specs - and a good tube can last a lifetime at ham intermittent use.  I have some 4-1000A's here that are still in service after buying them as pulls back in the mid-70's. That's what I run in Fabio now. These 4X1's always had glass Eimac chimneys and plenty of air thru them. And Lord knows I've been known to push them power-wise at times...


T

[Knightt150]

A 6146 is not going to last forever but my JOHNSON RANGER the early model one, have ran for years on the same 6146. I cant say for sure but the original 6146 taken care of could last for 50 years. If you dont run max out and take care of the finals they will last a long time. I don't use the ranger all year long the KNIGHT T150's are used in the summer months (to hot) in the ham shack.

John W9BFO

[KC4ALF]

The 6146's in my DX-100 and Yaesu Ft-101B have been in there from the 60's and 70's respectivly but I do run them conservativly it is true.

[W1AEX]

It seems that, as it is with many things, your mileage may vary. I installed three Zenith 6146B's in my Johnson Viking III in the late 70's and they still provide an easy 135 - 140 watts output with AM. They don't need much more than 6ma of grid current to produce full output with 650 -700 volts on them. The RCA 811A's that are in the modulator show no signs of struggling with the 1250 volts I feed them, and their age was undetermined when I got them back in the late 70's. I have 810's that were pulls from W1AW back in the 30's and they still work fine as modulators. I also have Eimac 4-400C's that were pulls from a local broadcast station back in the early 80's and they still come to life on those rare occasions when I power up the big rig. The old U.S. made tubes amaze me. Chinese made tubes... not so much.

[W2PFY]

I just put an old set of 100T's in my BC-610D this past week end. These are the earliest date of manufacture by Eimac. Probably from 1935 or 36.  The have open plates on them where you can look right down into the tube and see the filament and grid. There is no crown on the plates so all is visible. One has a lot of brown rings in the tube up from the plate area so it has been well used. The other looks like NOS. They modulate the transmitter to 150 percent pos peaks. Not bad for tubes that old. I just cannot believe that the builders of these tubes would have ever thought that they would still be serviceable after all these years.

[WB6NVH]

I used to work on a lot of Motorola and GE police and fire radios, and the 6146's would last a couple of years in regular service before needing replacement.  The ventilation was less than ideal and the filament voltage was always varying, which may have had something to do with it, along with vibration.

On the other hand, Motorola's first duplex mobile telephone used a 5894 in a PA which only ran it at 25 Watts.  I never found a bad one, even in phones which had been in service for 20+ years, and that PA is a continuous duty design which was often key down Class C for 5-10 minutes at a time.

[K1JJ]

Adequate tube cooling is important....


(picture coutesy, K5IIA)

[WD5JKO]

I have about 30 years now on a quad of Sylvania 7868's in my Sherwood S8000 30w / channel tube amplifier. I did regulate the voltages in 2003, and hold the cathode current to 20ma per tube (.02A X 450v = 9w Pd). Many tube audio amplifiers run the static current at the tubes pd ratings, or even higher. I run at about 1/2 the rating. This might cut down on the available power, but I don't experience that. The walls do rattle quite a bit when I use Netflix with the Wii and watch old episodes of '24'.

This amplifier is part of the home entertainment center where it is on pretty much whenever the TV is on. I figure an easy 50,000 hour estimated run time. I set the idle current back in 2003 after regulating the supplies, and I checked the current again last month. No change in 7 years! 

http://pages.prodigy.net/jcandela/Sherwood_S8000/HV_REG/S8000_Mods2.htm
(ignore pop-up)

Jim
WD5JKO