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Author Topic: Lifespan of 811A tubes.  (Read 9195 times)
W9KDX
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Posts: 770




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« on: March 29, 2012, 06:06:04 PM »

I know you guys won't go out on a limb and tell me any expected lifespan of 811A tubes because there are too many variables.  How about this; any idea of the lifespan of 811A tubes, assuming they are not defective and assuming that there are no defects in the amp circuitry, if they are only run at idle?  Just turned on, no transmitting?

Does that eliminate most problems?
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Sam
W9KDX
W8JX
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Posts: 5688




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« Reply #1 on: March 29, 2012, 06:28:46 PM »

Well even being just "on" the tubes will eventually loose emissivity and performance. The biggest wild card here it how hard you push the tubes. If you do not they can last many years but it you do it could be mere months or even weeks before they die if you push them hard enough (even one good "bad" tune can wreck tubes in a matter of seconds).
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AD4U
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« Reply #2 on: March 29, 2012, 07:06:15 PM »

My Collins 30L1 came with RCA 811A tubes when I bought it used in 1987.  I do not use the amp much, but the RCA 811A tubes are still going strong at around 700  watts out.  I doubt if the Chinese tubes will last as long.

Dick  AD4U
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K0ZN
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« Reply #3 on: March 29, 2012, 07:33:39 PM »

Candidly, it is almost impossible to make any reasonable accurate prediction. You will get responses all over the board.  With *good* quality tubes, operated
with in spec's and not cycled off and on excessively, you can expect "years".  You can also expect minutes or seconds if a bad mistake is made during tuning
or wrong antenna connected/disconnected, etc.

Not sure why you would never transmit with the tubes??  811A's are better off if they are CORRECTLY used periodically. The heating of the Plate helps
extend the life of the tube. Filaments only doesn't have much gettering effect. Very long periods of inactivity is not conductive to long life, either. 
I have and amp with Chinese 811A's in it. I have had a 50% failure rate over 6 tubes !! With the quality (lack there of) being what it is, really, the life of these "modern" 811A's is virtually UN-predictable from what I can see.

I don't think there is any realistic way to ACCURATELY answer your question due to all the variables, to be candid.

73,  K0ZN
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W4VR
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« Reply #4 on: March 30, 2012, 08:02:45 AM »

I had four of them in an old Heathkit Warrior which I purchased used in 1963.  I sold the amp 20 years later and the tubes were still putting out as much power as when I bought it.  I believe they were RCA tubes.  I can't say that the Russian or Chinese equivalents will last as long.
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N6AJR
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« Reply #5 on: March 30, 2012, 01:35:05 PM »

Tubes are like most electronic stuff. They usually fail on start up. or when something drastic happens. For instance , youa are in the middle of a QSO and the power goes out for 3 or 4 seconds. this will hit it hard, and could blow it up, but if you turn it on at least once a month or so, to keep all the innerds nice and  comfy, and don't over do it when transmitting, they could last for several decades.
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W9KDX
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« Reply #6 on: March 30, 2012, 03:33:09 PM »

Thanks.  It is on way more than a month or two.  It spends most of the time on standby just waiting.
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Sam
W9KDX
W8JX
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« Reply #7 on: March 30, 2012, 03:59:21 PM »

Thanks.  It is on way more than a month or two.  It spends most of the time on standby just waiting.

You know there really is no need to do this. The 811 like the 572 and 3-500z have a directly heated cathode (a thoriated filament) which mean they are basically instant on. It only takes a few seconds and it is ready to roll.
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W9KDX
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« Reply #8 on: March 31, 2012, 05:43:17 AM »

Thanks.  It is on way more than a month or two.  It spends most of the time on standby just waiting.

You know there really is no need to do this. The 811 like the 572 and 3-500z have a directly heated cathode (a thoriated filament) which mean they are basically instant on. It only takes a few seconds and it is ready to roll.

We seem to miscommunicate a lot.  The amp is on and waiting because I am not transmitting, I am listening.  I just happen to listen more than I talk. 
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Sam
W9KDX
WD8FM
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Posts: 8




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« Reply #9 on: March 31, 2012, 07:09:07 AM »

Thanks.  It is on way more than a month or two.  It spends most of the time on standby just waiting.

Kind of a waste of power sitting on standby, it still draws around 150 watts in standby.  If you dont use it, why have it?
 Smiley
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W8JX
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Posts: 5688




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« Reply #10 on: March 31, 2012, 08:42:41 AM »

Thanks.  It is on way more than a month or two.  It spends most of the time on standby just waiting.

Kind of a waste of power sitting on standby, it still draws around 150 watts in standby.  If you dont use it, why have it?
 Smiley

I agree and given that it is basically instant on I would not waste energy or tube life using them as light bulbs on standby.
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W9KDX
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« Reply #11 on: March 31, 2012, 07:26:57 PM »

So you are saying I should turn it on and off and on and off and on and off as I need it?  It could be on and off as much as 20 times in a few hours.  This is really better for the amp?
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Sam
W9KDX
W8JX
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« Reply #12 on: March 31, 2012, 07:42:05 PM »

You started by saying it was one standby most of the time. Leave amp off until you really need it it is only going to give you a S-unit or so over barefoot anyway. I turn my amp off when not using it.
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KD8MJR
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« Reply #13 on: April 01, 2012, 02:17:48 AM »

I thinK you guys might be missing his point.
I think he is saying that he is part of ragchewing group but he's not an active talker.
But he still needs to be ready to transmit if a question is thrown his way.
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N3QE
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Posts: 2167




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« Reply #14 on: April 01, 2012, 05:30:05 AM »

So you are saying I should turn it on and off and on and off and on and off as I need it?  It could be on and off as much as 20 times in a few hours.  This is really better for the amp?

"As you need it" would mean, to most hams, that they keep the amp's main power switch on while they are in the shack and want to be ready to transmit. Meaning the amp's power switch gets flipped a few times a day, not 20.

Turning the power switch on and off a few times a day will match what 90% of hams are doing. The other 10% leave the amp on in winter 24x7, for no other reason than to keep the shack warm.

Contesters and some other unusual usage patterns excepted. Your usage pattern and actual transmit fraction is very very similar to the vast majority of hams outside of contest weekends.

There are nutcase exeptions. I remember a guy with a hybrid Kenwood transceiver who flicked the switch on the front panel to turn off the tube (6146B type... and maybe the driver tube too?) filaments every time he went to receive, all in the name of extending tube life. Nobody in the club was surprised that he needed that switch replaced several times a year at a cost of several times what a set of tubes was! I think that switch was there for mobile users so that the filaments wouldn't run down the car battery unnecessarily while parked.

Tim.
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