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Author Topic: tube service life  (Read 1101 times)
N3OQD
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Posts: 104




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« on: October 21, 2007, 07:42:43 PM »

Within design peramitors of the Ameritron AL-811(H) what is the average useable lifespan in ICAS specs do the 811a's last.  If upgrade to the 572b's does that figure change.  Ameritron says of the AL-811(H) that "they last a long time", whereas in their AL-80B it states that the 3-500z lasts "16,000 hours ICAS".  I know that they are both directly heated thoriated triodes.  I also have the common sense to not run the amp hard or for long extended duty cycle.  Thanks.
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KA5N
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« Reply #1 on: October 22, 2007, 02:36:56 AM »

I find that most things last at least one day past the warranty period.
Allen
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K0BG
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« Reply #2 on: October 22, 2007, 06:06:09 AM »

One of the biggest problems with 811a equipped amplifiers, is 95% are over driven! If designed correctly, full output occurs with just about 65 watts of drive, just like Ameritron's instructions state. As a result of over driving them, tube life is greatly shortened. I've seen Collins 30L1s, go 10 years before needing new tubes, and the 811H will too, if driven moderately.

The myth about 811 amplifiers in general is, folks think that by replacing the finals with 572Bs, their tube life problem will be solved, and it very well might. However, the power supply is still what it was before the change out, and THAT is the limiting factor.

Alan, KØBG
www.k0bg.com
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W5KG
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« Reply #3 on: October 22, 2007, 07:43:15 AM »

Charles, a friend of mine has the original 811a tubes in his AL811H that came with it in 1999. He does not abuse them while tuning and drives them with about 60w. He also uses the amp every day. So 8yrs is not bad.
The question is; is it worth the cost difference to justify going to 572B tubes when it it time to change? I don't think so. $80 vs $200 no way and you are not going to get any more power out, although some may try to tell you will.
I can hear them now!
btw, I have had AL811, 811H and 30L1. I tried 572Bs in the 811 and 811H with no difference in output so I pulled them reinstalled the 811s and sold the 572Bs.
Hope this helps
Don, W5KG

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KE3WD
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« Reply #4 on: October 22, 2007, 08:40:46 AM »

Alan is telling you the full skinny on the subject.  

You may not find 811s getting the ICAS rating, they were never considered to be commercial grade transmitting tubes while the venerable 3-500Z was once the low power workhorse of the AM band...

I've found 30-L1's with the original tubes still in them that still had fairly stout output -- there is no need to run the exciter past the 70W mark at all, matter of fact I just leave mine there for both "barefoot" and when I turn the amp on, doesn't make enough difference, those "missing" 30 watts.  Rig lasts longer, too.

Those that refuse to hook up the ALC and use it are also courting shortened tube life, too.  Along with other things that make hamming hard for those upband of them.  The argument that ALC overshoot happens doesn't make much sense either, the amount of overshoot is orders of magnitude below what can happen with no ALC operating.  A little overshoot for a few mS at a pop versus steady state overdrive...


KE3WD
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N3JBH
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« Reply #5 on: October 22, 2007, 01:50:55 PM »

"You may not find 811s getting the ICAS rating, they were never considered to be commercial grade transmitting tubes"

That is an interesting statement Mac.  Leads me to ask if the 811A was even really intended as a tube for rf service in the beginning. I know it seen life as an audio tube in audio amplifcation uses. So i just can not help wondering if it was a audio tube that found it's way in the RF world. Or a Rf tube that found it's way into the audio world.

Jeff N3JBH
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W2VW
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« Reply #6 on: October 22, 2007, 06:06:31 PM »

Regarding ALC overshoot. Have you anything besides gut feeling to back this statement up?
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KE3WD
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« Reply #7 on: October 22, 2007, 06:21:19 PM »

>>Regarding ALC overshoot. Have you anything besides gut feeling to back this statement up? <<

Only going on close to 50 years of esperience backed by data taken with oscilloscopes, real time analyzers, test sets, datalogging equipments, frequency analyzers and a few other apparatus.

I've worked at type acceptance labs for commercial stuff, too, as well as just being the "lowly" service tech or station engineer.  


But don't take my word for it, the information is in writing in many places.  ARRL tests and procedures is a good starting place, but don't just take their word as gospel either.  Get a compendium of research data -- and start taking your own measurements also.  


KE3WD
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KE3WD
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« Reply #8 on: October 22, 2007, 06:22:55 PM »

"eSperience"?  


si.



LOL



Don't worry, what I have to say makes too much damn sense for hams to want to follow.  There will be plenty of hash all over the bands for years to come no matter what.


KE3WD
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K6AER
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« Reply #9 on: October 22, 2007, 08:08:16 PM »

Most of today’s modern transceivers (within the last 5 years) don’t suffer from overshoot of the ALC like the older rigs. With the exception of the tubes being overdriven, the duty cycle of a tube in SSB mode is very low and in the order of 20%. Band splatter is generally a result of not ALC being connected but the drive level being improperly set. If your radio does not suffer from overshoot with the internal ALC it will not overdrive the amplifier. Your amplifier is linear from a few milliwatts to its rated output.

My Alpha amps use 3CX800A7’s (considered most fragile by ceramic tube standards) and they are over 20 years old and they get used several times a week. They still put out full power but then I don’t overdrive the tubes and keep the grid current within specifications.

I don’t use the ALC and it is not necessary if the amplifier drive and radio are set up properly.

I think ham radio is the only aspect where external amplifiers are connected to ALC loops. Broadcast stations just set the drive levels properly to maintain linearity. They have lots of other alarms but I have never seen a ALC loop on a 50,000 watt transmitter.

If some one can give a real example I like to know.
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N3OQD
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Posts: 104




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« Reply #10 on: October 23, 2007, 11:10:30 AM »

   I appreciate the varied comments.  I was unaware that so-o-o-o many people overdrive the AL-811(H).  As for myself, I usually drive my amp with about 30 to 50 watts SSB.  More often than not, I stay at about 35 to 40 watts drive about 90% of the time.  I also use cut peices of masking tape to mark optimum settings.  This way, for the most part, I usually don't have to tune up to search for the spots much anymore.  If I desire more power, then a bigger amp is the way to go, period.  I do not use audio compression or processing of any type.  As for now, with this modest drive, I can usually talk to anyone I hear and that is all that counts for me.  I also like my things to last along time as well.  Thanks.
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W2VW
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« Reply #11 on: October 23, 2007, 05:06:30 PM »

   ALC is like religion. Some people write it off and some people follow it where it takes them. This is why I asked the question.
   We both know how difficult it is to test for overshoot.
   There are some rigs that have much worse ALC than others. The S-Line would be an example of one rig that I would (and have) enabled an ALC loop. Certain others that I've used have single ended gain controlled stages with a time constant that makes transients a fact of life. The old trick of using a push-pull stage with the gain reduction applied in parallel is a nice way to eliminate unnecessary distortion. Transistor ham rigs that don't even take this basic step should have their ALC port filled with concrete IMHO.
   It would really be nice to see some test results of different ssb exciters when leaning into ALC. I've read everything that I can get my hands on and don't remember ever seeing a test layout dedicated to this.         The entire concept put forth on ham BBoards of using ALC as some sort of protection against overdrive seems contrary to good amateur practice to me. If a ham cannot figure out how to reduce drive then maybe it IS time for regulation by bandwidth and techincal proof stickers good for 1 year.
   I have a little on air experience and have spent lots of time listening to unwanted byproducts of phone transmitters on H.F. My feeling is somewhat different than yours.
   That bit about lowly station engineers really hurts.
:0
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KE3WD
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« Reply #12 on: October 23, 2007, 09:43:55 PM »

It read, "lowly technicians AND station engineers" and was meant in the humblest of terms, having served as both.  First thing I noticed was all the "engineers" who had no experience as service technicians under their belts -- and what they knew vs what they thought they knew, what they could -- and many times could not do.  Like troubleshoot, for example.  

You made the comment about what has happened to the Amateur Service yet in the same breath proclaim to the amateurs on this forum that they don't need to use the ALC, think about that long and hard, now, you hear?  

Experience is one thing and old hands can get away with doing a lot more things a lot more different ways than the current influx of new hams we are enjoying can.  There seems to be a trend happening here of late, first buy the rig, then find out that the compromise antenna doesn't live up to the advertising claims -- so then the desire for the amplifier hits hard.  Too hard, actually, for those of us in the know keep saying over and over, "antenna, antenna, antenna" -- but I would like to see Ameritron's sales for the last quarter even though I know it is a safe prediction to say that RF linear amplifiers for the ham bands are selling like hotcakes on Sunday mornin' of late.  And they can't keep the bipolar transistor "no tune!" beasties on the shelves.  Telling people that new to the art and craft of radio that they don't need to hook up ALC on one of those is the recipe for what you are going to get on the bands, man.  Overdriven bipolar hash bordering on spurs.  

Hookup, setup and proper use of the ALC might go a long way towards preventing that from happening.  

Just sayin'...


KE3WD
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K7GRR
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Posts: 50




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« Reply #13 on: October 27, 2007, 11:48:46 PM »

Regarding overshoot:

I have a couple of WaveNode sensors in my shack, and a 1 year old FT857D (and an AL-811H) etc, etc.

This is a 'modern' radio.
Test after test, regardless of RF power setting, the 857 shoots a 160 watt (on average) pulse of RF before the ALC throttles things down.  It's very short, but it's there and repeatable.  Is it a problem?  I don't think so, but thought I'd throw that in.

I'm in the 'if you don't hook up the ALC, you're an idiot' camp, because I'm an idiot and I can easily see working a local with the amp on standby, then catching Russia and flipping the switch and shooting 100 watts into my amp.

Regarding tube life:
Back off on the drive power, all will be well.  I can tune 600W key down, but then back off to about 500W key down.  Happy tubes, and the guy/gal at the other end will never know that you're loafing.
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WA9SVD
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« Reply #14 on: October 28, 2007, 04:01:53 PM »

The myth about 811 amplifiers in general is, folks think that by replacing the finals with 572Bs, their tube life problem will be solved, and it very well might. However, the power supply is still what it was before the change out, and THAT is the limiting factor.

Alan, K�BG
www.k0bg.com  

======================

    To add to Alan's comment, 572's won't SOLVE any problems; in fact, they may only aggravate a situation.

    As he said, one of the greatest reasons for premature 811 failure is being overdriven.

    One of the BIG problems is that while the 572's are more rugged, and they don't produce more OUTPUT, they can withstand a greater degree of overdrive without failure, but that only makes a signal dirtier.
    More tolerance to overdrive is NOT an advantage; in fact early 811 failure should be a wake-up call that the tubes are likely being driven too hard, or some other operator-induced problem exists.  572's don't really SOLVE any problems.
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