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Author Topic: Indirectly Heated Valve (Tube) Longevity Question.  (Read 16511 times)
MM0IMC
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Posts: 218




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« on: December 06, 2017, 05:46:18 AM »

Hi folks,

Can anyone tell me if repeated on-off cycling (normal daily use) of an amplifier using an indirectly heated valve (tube) can shorten the life of the valve (tube), please? The amplifier uses a Russian NOS GU-74B tetrode.

73,

Ian - MM0IMC.
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VK3BL
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« Reply #1 on: December 10, 2017, 05:09:23 AM »

Hi folks,

Can anyone tell me if repeated on-off cycling (normal daily use) of an amplifier using an indirectly heated valve (tube) can shorten the life of the valve (tube), please? The amplifier uses a Russian NOS GU-74B tetrode.

73,

Ian - MM0IMC.

Doubtful.  I never snapped a filament in any 811A or 572B, but I sure as heck burnt through plenty in mere months leaving them running in standby.

Turn it off if you're not going to use it within 30 minutes; only turn it on if its Rare DX or you have too.

If you want to leave the amp on whilst at work, or 'just because', solid state pays for itself quite quickly, even if you occasionally blow some FETs.
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
N3QE
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« Reply #2 on: December 10, 2017, 12:22:56 PM »

Can anyone tell me if repeated on-off cycling (normal daily use) of an amplifier using an indirectly heated valve (tube) can shorten the life of the valve (tube), please? The amplifier uses a Russian NOS GU-74B tetrode.

There is no risk to tube life in on-off cycling a GU74B or most other ceramic tubes.

Most oxide coated cathodes are rated for overall power-on hours of 10,000 to 20,000 hours. I don't know the exact rating for the GU74B but considering its original military application it is very doubtful to be longer than 20,000 hours. 20,000 hours is about 2 years 24x7.



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KM1H
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« Reply #3 on: December 11, 2017, 12:15:12 PM »

The Russians are happy if they make 1000 hours
https://frank.pocnet.net/sheets/018/g/GU74B.pdf

In commercial ham amps they are run way over spec and called the 4CX-800A and often go flat in 2-3 years of heavy use of excessive power. Run by the spec of 600W PD and 550W per tube output and they may last a long time.

Carl
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K6AER
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« Reply #4 on: December 11, 2017, 05:22:09 PM »

I have found the Russian Gu-74B's in the Alpha 87A will last a very long time if the power is limited to 1500 watts out. The tube will as Carl had mentioned go soft if abused or you try to get 2300 watts out in the contest mindset mode. My 87A backup amp is performing on the Russian tubes for the 8th year.
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KX2T
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« Reply #5 on: December 11, 2017, 08:03:57 PM »

You all seem to have lots of experience with the Russian tubes, W8JI has dowm played them for years over the old gold standard Eimac tubes but I remember Eimac did have a few years back in the 1980ies were there 8877 was having more than a few problems with new production tubes. Threw the years I have run amp's with 8877 tubes without issue, never had one go bad even if a guest op didn't know about grid current and have never seen one go soft at 1500W out during any contest but have never done RTTY contest. I have also owned the Alpha hybrid 91b for over 6 years during my contest time when we built W2A station and ran them at 1500W all weekend long year after year and never seen any loss of output on two of those amps but I have seen friends with Alpha 87A have those 3CX800A pop like candy after a few years at 1500W.
I have also know fellows run those 91B amps with the GU74B tubes flat out at 2.5K and have never replaced those tubes, maybe they got a good pair not the crap that is un tested from some internet tube hustler. How long tubes last depends on were they are purchased from  plus incorrect operating practices but starting old wives tales just because the tube was made in Russia but China is another story cause they need to go threw production changes which takes years for them to get it right.
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MM0IMC
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« Reply #6 on: December 12, 2017, 04:48:58 AM »

I've had my Alpin 100 MK III for several years now and run it up to the UK legal limit of 400W PEP, on both phone and SSTV.  It has a GU-74B tetrode in it and it's been a faultless amplifier and valve (tube).  Wink
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KM1H
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« Reply #7 on: December 12, 2017, 10:20:02 AM »

I
Quote
've had my Alpin 100 MK III for several years now and run it up to the UK legal limit of 400W PEP, on both phone and SSTV.  It has a GU-74B tetrode in it and it's been a faultless amplifier and valve (tube).

At that power level you could run sweep tubes or 811A's.

I do not know the filament life expectancy of the GU-74B (unless it is part of the 1000 hour spec) but it is not a tube Id leave running 24/7 or even many hours without being driven. The same holds for any indirect heated tube.

Carl
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MM0IMC
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« Reply #8 on: December 12, 2017, 02:42:19 PM »

On the odd occasion when I've kept the amplifier on standby all day, it's only been for less than 30 days out of the total of nearly two and a half years.  I used to have an Ameritron AL-811H, but found that the valves (tubes) didn't like high duty cycle modes like RTTY, SSTV, etc. even at 400W PEP.  I also wanted an amplifier that I could use on 6m, the Alpin 100 MK III met that criteria.
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VK3BL
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« Reply #9 on: December 12, 2017, 08:51:34 PM »

On the odd occasion when I've kept the amplifier on standby all day, it's only been for less than 30 days out of the total of nearly two and a half years.  I used to have an Ameritron AL-811H, but found that the valves (tubes) didn't like high duty cycle modes like RTTY, SSTV, etc. even at 400W PEP.  I also wanted an amplifier that I could use on 6m, the Alpin 100 MK III met that criteria.

The tubes themselves are not the issue; a quad of 811As is perfectly fine for those modes and duty cycles. 

The issue is the amplifier itself - its biased for SSB usage and unless tuned precisely its pretty easy to cook the tubes.

Still, my AL-811 tuned precisely actually showed less plate colour running JT65 than SSB...
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
K6BRN
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« Reply #10 on: December 12, 2017, 09:37:48 PM »

Jarred (VK3BL):

I'm surprised that the 811As can do a high duty cycle mode like JT65 reasonably well.  You must keep the output fairly low (200W or less?) to avoid over-stress them during the relatively long TX interval.

Brian - K6BRN
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MM0IMC
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« Reply #11 on: December 13, 2017, 01:54:11 AM »

Believe it or not, I do actually miss my old AL-811H. I'm tempted to get another just to enjoy the glow from the valves. Grin  Either that or the AL-80B. Shocked
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KX2T
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« Reply #12 on: December 13, 2017, 06:40:46 AM »

Some here just like to bash the Russian tubes, they state all kinds of BS on these forums without really having used them in an amp for any length of time, its a bunch of hearsay and conjecture started with a bunch of old timers who never knew anything but Eimac. I have used both Svetlana and Eimac tubes in a wide variety of amps and the only tubes that had a short life spans were the Chinese 3-500Z, never used any sweep tube amps or 811A Chinese tube amps only the old Collins 30L1 or Cetron 572B's in an old SB200 but the China made tubes don't last, I get that from many of my friends I talk with who have had the china made 8877 in there Alpha amp's and maybe get 3-4 years out of them compared to the Eimac brand so you get what you pay for.
With the Russian tubes there are GU74B tubes made in 2017 which are starting to show up in the market place, I believe the ones sold by DX engineering are the newer production tubes at $350 a pop and the ones out of Russia that are around $300 plus shipping and duties which are about the same once brought into the USA, still a far cry from the list of 3CX800A7 Eimac's at over a kilobuck per tube. I have used NOC GU74B tubes in my amp that were a date code of 1991 without any issues and they are from the Russian surplus market but for a little more you can buy new production tubes and besides what some will say here are far more rugged than the 3CX800A7 Eimac I used in older Alpha amps. Your mileage may vary but that's my 2 cents.
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N9AOP
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« Reply #13 on: December 13, 2017, 08:21:35 AM »

I have an Acom 1000 with the GU74B tube.  I run it for an hour at 7AM and an hour at 7PM and turn it off in between.  It has been 25 months now and the amp still works as it did when I got it.  I run a digital mode at 800W and that makes the SSB at about 1 Kilo.
Art
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KM1H
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« Reply #14 on: December 13, 2017, 02:24:33 PM »

Quote
Some here just like to bash the Russian tubes, they state all kinds of BS on these forums without really having used them in an amp for any length of time, its a bunch of hearsay and conjecture started with a bunch of old timers who never knew anything but Eimac.


Most of the bashing Ive read or heard OTA is well deserved.

I also have a copy of the original Svetlana engineering tests run on the GU-74B when George Badger, W6TC, who ran Svetlana USA wanted to call it the 4CX800A. The IMD was horrendous when pushed beyond their 600W Pd rating. George wanted a 2500W capable amp and sold as 1500W; he was also in Marketing and Sales Engineering at Eimac for decades.

Quote
I have used both Svetlana and Eimac tubes in a wide variety of amps and the only tubes that had a short life spans were the Chinese 3-500Z, never used any sweep tube amps or 811A Chinese tube amps only the old Collins 30L1 or Cetron 572B's in an old SB200 but the China made tubes don't last, I get that from many of my friends I talk with who have had the china made 8877 in there Alpha amp's and maybe get 3-4 years out of them compared to the Eimac brand so you get what you pay for.

All that tells me is they dont know how to use them or are pushing beyond the limits; typical ham practice.
Quote
As you said above its a bunch of hearsay and conjecture started with a bunch of old timers who never knew anything but Eimac
.  Eimac gave the Chinese the 8877 tooling and commercial users report as good as or better than Eimac life. The Chinese 3CX3000A7 is another great tube at half the price of Eimac.

Quote
With the Russian tubes there are GU74B tubes made in 2017 which are starting to show up in the market place, I believe the ones sold by DX engineering are the newer production tubes at $350 a pop and the ones out of Russia that are around $300 plus shipping and duties which are about the same once brought into the USA, still a far cry from the list of 3CX800A7 Eimac's at over a kilobuck per tube.

I may be wrong but Id suspect those are NOS tubes that have been washed and relabeled. Standard practice in the shady side of the tube business for many decades.

Carl
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