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Author Topic: Indirectly Heated Valve (Tube) Longevity Question.  (Read 17311 times)
MM0IMC
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Posts: 255




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« Reply #30 on: December 16, 2017, 02:01:58 AM »

So, does that mean I should sell my amplifier and go for something with less IMD products then?  Huh That's somewhat rhetorical, as I've a lot of money invested in it.  I wish I hadn't asked the original question now... Undecided

Realistically though, every ham should endeavour to emit the cleanest signal possible with the lowest possible IMD products, best linearity and best spectral purity they can!
« Last Edit: December 16, 2017, 02:21:22 AM by MM0IMC » Logged
G3RZP
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« Reply #31 on: December 16, 2017, 02:47:28 AM »

If you have a solid state exciter - unless it's SDR with an input for pre distorting - the probability is that especially the high order IMD that really causes problems to other band users is determined by the exciter and not the tube amplifier.

Back when there was a lot of point - to - point HF traffic, it was usual to have a 12kHz wide signal i.e. 2 3kHz telephone channels each side of the partially suppressed carrier. 2 tone IMD was specified as -36dB relative to tone or -42dB relative to PEP. It doesn't really matter whether or not you measure relative to tone or to PEP as long you specify which.
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VK3BL
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« Reply #32 on: December 16, 2017, 03:58:08 AM »

So, does that mean I should sell my amplifier and go for something with less IMD products then?  Huh That's somewhat rhetorical, as I've a lot of money invested in it.  I wish I hadn't asked the original question now... Undecided

Realistically though, every ham should endeavour to emit the cleanest signal possible with the lowest possible IMD products, best linearity and best spectral purity they can!

Of course not; its perfectly fine for Ham usage Smiley  Just don't leave it on when not in use; advice that applies to any tube amplifier.

The "creatively named" 4CX800A (GU-74B) just isn't in the same class as the medical grade 3CX800A7, but it can be had for 1/10th of the price.  Like all amps based around cheap tubes, the designers typically don't give a second thought to pushing them harder than the datasheet.  Often, this necessitates the use of additional engineering tricks such as 'electronic bias' systems, which I'm no great fan of either.

All that said, your amp is likely cleaner than my top dollar THP 2.5Kfx, which runs about -30dBc IMD3, and has in band harmonics that tend to go on for quite a bit.  I can leave mine on 24/7 though without spending a few hundred in tubes a year Smiley

As G3RZP points out, the exciter will almost certainly be the weak point; that or another component in the TX chain such as the antenna system, or even a metal gutter nearby.

FYI, you can check out what a typical 12v exciter, and 12v exciter / SS amp combo looks like IMD wise in my IC-7610 2 tone test video here:
https://www.youtube.com/watch?v=Sc_6ST5NK3k

As seen in the video, the key to getting the most out of your setup is to find the sweet spot, and do everyone a favour and don't try and get every last watt out of it.

Nowadays it costs less than $400 USD in equipment to accurately measure your system performance; don't let opinions make you feel worse about your pride and joy when you can look at the facts for yourself.
« Last Edit: December 16, 2017, 04:21:48 AM by VK3BL » Logged

J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
KX2T
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« Reply #33 on: December 16, 2017, 07:14:58 AM »

If you listen to Lord Karl and his dis belief of either Radcom's or the ARRL lab reviews  of amp's which run the GU74B tubes yes you now own a sputtering IMD amp yes an I am going to believe some self proclaimed expert on this, I dont think so. What I do know is that the Acom amp I do own not only has been tested by the ARRL labs at a 3rd order IMD of  -44Db down at 1KW output and I have also tested it with a spectrum analyzer that I had on loan from an engineering buddy and depending on which exciter I used was -35 to -42db down on the third order IMD. So if you want to believe that some guy on these forum's is going to tell you your amp is crap  then sell it but as for me no friggin way, I have done enough research to know he is way out of line.
BTW that other amp in Bulgaria looks to me that they did exactly what Acom did but there using a different transformer, another very well designed European built amp.
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MM0IMC
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« Reply #34 on: December 16, 2017, 10:11:26 AM »

Don't worry, I'm in no hurry to get rid of my Alpin amplifier, as I'm in love with it!  Cheesy

Somebody said that Europeans are "cheaper", well I resemble that remark!  Grin But honestly, there's nothing particularly cheap about these amplifiers, my cost an eye watering £2,250 which in no small sum. The build quality is far superior than the Ameritron AL-811H that I used to own. Don't get me wrong, I'd buy another Ameritron as I do like them.  Shocked
« Last Edit: December 16, 2017, 10:13:49 AM by MM0IMC » Logged
KM1H
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« Reply #35 on: December 16, 2017, 11:19:40 AM »

Quote
Personality aside, Carl's history lesson is correct.

Thank you Geoff and Ive always found Aussies to be well ahead of the curve on technical ability. Unfortunately I have to put up with a member of the bottom on here but after all his contest station SSB signal was well known as among the worst.

Quote
Isn't that the truth

http://www.eham.net/ehamforum/smf/index.php/topic,104518.msg861094.html#msg861094

Thought I'd save someone the trouble .

P.S. How ya doin Carl ?

Thanks for that link which adds other links to study but Jimmy would be lost at the first post and his only ability is insults anyway and is easily ignored.

Im doing fine, getting vehicles ready for the winter kinda late. Temps in the teens and low 20's puts a crimp in my tower climbing.

Carl

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K6BRN
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« Reply #36 on: December 16, 2017, 11:33:15 AM »

Its pretty clear that you all have terrible, terrible amplifiers.

Decaying old USA tubes, Russian tubes labelled in Cyrillic, Chinese tubes... etc.  All glass and brittle ceramic, all hot enough to burn with lethal voltages inside.  Terrible, terrible IMD (Horrors) Tsk!

And its not as if any of them actually work, right?  Because if they DID work then it would simply be a friendly discussion of which I prefer - the transparent, warm "glowy" kind or the staunch, white-starched and intimidating "dressed for success" ceramics.  The Roooshin ex-military surplus or the ChinaCo copies.

As a founding member of S.P.I.T.  (Society for Prevention of Injury by Tubes), I'm willing to help (its part of the ham and Boy Scout code) by offering you all the opportunity to ship your awful amplifiers, tubes included, to me, C/O the TRW Swap meet, for proper disposal.  I pretty much guarantee we'll find a use for them.

NEXT TOPIC:  Those wonderful, amazing and dirt cheap LDMOS solid state amps that are now blazing into the ham market.  Perfect signals out, sipping power from 9-volt smoke detector batteries.  Suitable for welding on your off days.  You know.  Perfect.   Not much to discuss, I guess.

Well.... Happy Holidays, all.  and I hope you all get the amplifier of your dreams.  Smiley
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KM1H
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« Reply #37 on: December 16, 2017, 11:38:34 AM »

Quote
So, does that mean I should sell my amplifier and go for something with less IMD products then?  Huh That's somewhat rhetorical, as I've a lot of money invested in it.  I wish I hadn't asked the original question now... Undecided

Realistically though, every ham should endeavour to emit the cleanest signal possible with the lowest possible IMD products, best linearity and best spectral purity they can!

I never suggested anything poor with your amp at your 400W legal limit. OTOH a lot related with IMD is the tuning used plus VSWR with tetrodes, and I would suggest borrowing one of the later rigs with a built in spectrum analyzer. Experiment with various tuning schemes and write down all settings, including drive, for all bands used.

My own always connected setup, at the flip of a switch, is an ancient HP 141T  I retired from the lab bench about 16 years ago. As a major heat generator, and getting harder to service, it is turned on only when I feel it necessary.

Having worked in the RF field since 1963 from tech in the ham related plus military products division of National Radio Company to Sr Engineer/Project Leader for military R&D for a leading UK company here locally I feel I speak with some prior knowledge....no matter what Jimmy babbles and blusters about.  

Carl
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KA5COI
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« Reply #38 on: December 17, 2017, 03:44:53 AM »

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.
Just getting back active, unless the rules have changed, 1500 watts is the limit.
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G3RZP
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« Reply #39 on: December 17, 2017, 05:45:20 AM »

Quote
Just getting back active, unless the rules have changed, 1500 watts is the limit.

I seem to remember some 50+ years ago (when the limit was 1kW input) reading about a W6 caught running 10kW. As it was AM, that probably meant around 30+kW out of the mains supply, and not I presume at 110 volts! Thus the term 'California kilowatt' for people running real QRO came into being.

Going back to the OP, I don't see any reason why indirectly heated cathode valves in transmitters shouldn't  last as long as in receivers - and there are plenty of WW2 vintage ex-service transmitters and receivers with original indirectly heated valves still in regular use.
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W1VT
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« Reply #40 on: December 17, 2017, 07:11:38 AM »

If you are really worried about transmit IMD these days, there is no need to rely on the ARRL or RSGB for test data.  You should be able to buy a brand new spectrum analyzer for around $700, which is in the same ballpark as a set of new tubes for your legal limit amplifier.  This  will allow you test the tubes under whatever testing standard you feel is appropriate.

Zack W1VT
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KM1H
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« Reply #41 on: December 17, 2017, 08:36:28 AM »

Quote
I seem to remember some 50+ years ago (when the limit was 1kW input) reading about a W6 caught running 10kW. As it was AM, that probably meant around 30+kW out of the mains supply, and not I presume at 110 volts! Thus the term 'California kilowatt' for people running real QRO came into being.

10KW carrier = 40KW PEP OUTPUT for 100% modulated DSB AM
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MM0IMC
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« Reply #42 on: December 17, 2017, 10:26:38 AM »

Quote
I seem to remember some 50+ years ago (when the limit was 1kW input) reading about a W6 caught running 10kW. As it was AM, that probably meant around 30+kW out of the mains supply, and not I presume at 110 volts! Thus the term 'California kilowatt' for people running real QRO came into being.

10KW carrier = 40KW PEP OUTPUT for 100% modulated DSB AM

That's considered QRP is some European countries and parts of the Russian Federation. Grin
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AE5GT
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« Reply #43 on: December 17, 2017, 02:10:52 PM »

Repeated thermal cycleing of just about anything  will shorten its life .  Unless you are heating to the point of binig molten ,The object expands on startup and contraction on cool down , This introduces stress into whatevere is being heated . Eventually you get fatigue .

Basically your bending it back and forth till it breaks.





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MM0IMC
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Posts: 255




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« Reply #44 on: December 17, 2017, 02:52:20 PM »

Repeated thermal cycleing of just about anything  will shorten its life .  Unless you are heating to the point of binig molten ,The object expands on startup and contraction on cool down , This introduces stress into whatevere is being heated . Eventually you get fatigue .

Basically your bending it back and forth till it breaks.







There's a name for that, but can't remember what it is. Huh I'm sure somebody will be along in a minute and enlighten me. Grin
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