eHam

eHam Forums => Amplifiers => Topic started by: MM0IMC on December 06, 2017, 05:46:18 AM



Title: Indirectly Heated Valve (Tube) Longevity Question.
Post by: MM0IMC 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.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: VK3BL 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.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: N3QE 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.





Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KM1H 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


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: K6AER 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.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KX2T 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.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: MM0IMC 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).  ;)


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KM1H 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


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: MM0IMC 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.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: VK3BL 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...


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: K6BRN 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


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: MM0IMC 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. ;D  Either that or the AL-80B. :o


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KX2T 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.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: N9AOP 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


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KM1H 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


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: K4RVN on December 14, 2017, 02:55:23 PM
It appears to me that the indirectly heated  valve or tube was not considered in some of the replies.  Mixing apples and oranges, to coin a phrase, will not answer the posted question. Tubes  indirectly heated normally have a longer warm up in order to get the tube heated for HV. application. Also they cost a lot more. If I'm wrong please correct me. Tubes such as the 3-500, 811A, 572B should not be used to compare is my understanding. Just trying  to get the facts not to be contrary. I have an AL 800H with 3CX800 A7 ceramic tubes that requires a 3 minute warm up and before it can be operated. I do not leave it on except for a few minutes cool down time at the end of use. Wear on the blower and reduced life due to hours of operation is enough to turn the amp off.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: MM0IMC on December 14, 2017, 03:06:32 PM
I can't speak about the life expectancy of the American 811A valves, as I've no experience of them. The Chinese ones do seem to be a mixed bag, to be honest.  As for the Russian valves, again, I've no experience with their version of the 811A's.  I do like the Russian ceramic valves though.  I get the feeling that there's somewhat of a bias against their valves (excuse the pun), perhaps based on old cold war ideology. :-\  I don't think this sentiment exists so much in Europe, though...


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KM1H on December 14, 2017, 03:40:27 PM
 
Quote
I do like the Russian ceramic valves though.  I get the feeling that there's somewhat of a bias against their valves (excuse the pun), perhaps based on old cold war ideology. Undecided  I don't think this sentiment exists so much in Europe, though...

Europeans appear to be cheaper in general than the US and take less interest in the quality of their signal. IMD was never an important consideration to the Russian military and most of their tubes are very poor in that regard.
It has nothing to do with any US-Russia snits.

Carl


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: K8BYP on December 14, 2017, 03:59:10 PM
YES its bad. ITs not about being "on" its about the 2X filament current at startup.

I just talked to a Broadcast Engineer who mentioned having to start up high power tubes S-L-O-W-L-Y to keep heater current down during cold startup.

Its a large mechanical shock to pass 2X rated current through the filament.

The filament (s) current, for example, in a Drake TR-3 is 11A cold and 5.5A hot.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KM1H on December 14, 2017, 04:56:22 PM
Quote
The filament (s) current, for example, in a Drake TR-3 is 11A cold and 5.5A hot.

So what? All those tubes have a controlled warm up filament in case you didnt notice and the radio is not Instant On.

This goes back to the 50's when series strings were showing up in multi tube radios and soon TV sets.

Most small signal tubes with an A suffix were the controlled versions and sweep tubes started close to the beginning such as the 12JB6 or the 6GJ5 for National before switching to the 6JB6A where the A meant something else.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: MM0IMC on December 15, 2017, 01:33:31 AM
Quote
I do like the Russian ceramic valves though.  I get the feeling that there's somewhat of a bias against their valves (excuse the pun), perhaps based on old cold war ideology. Undecided  I don't think this sentiment exists so much in Europe, though...

Europeans appear to be cheaper in general than the US and take less interest in the quality of their signal. IMD was never an important consideration to the Russian military and most of their tubes are very poor in that regard.
It has nothing to do with any US-Russia snits.

Carl

I looked at both the manufacturer's claimed IMD figures and those tested in a RadCom review, both are comparable to other amplifiers that I see on the market at the moment...

http://www.alpinamplifier.com/products/alpin-100 (http://www.alpinamplifier.com/products/alpin-100)
http://www.alpinamplifier.com/products/images/RadCom%20Review.pdf (http://www.alpinamplifier.com/products/images/RadCom%20Review.pdf)
http://www.alpinamplifier.com/products/images/FunkAmateurReview.pdf (http://www.alpinamplifier.com/products/images/FunkAmateurReview.pdf) Unfortunately, my German is very rusty...

I looked at other manufacturer's claimed figures, like Ameritron using Eimac valves, OM Power and Acom using Russian tubes. They all  quote nearly the same IMD figures, give or take a few dB.

I'm not an expert, just a layman trying to make some headway with this stuff. So, if I'm wrong or am looking at the figures wrong, please point me in the right direction.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: MM0IMC on December 15, 2017, 07:50:28 AM
I wrote to Veselin LZ1HD, who makes the Alpin range of amplifiers regarding the maximum power ratings of the GU-74B tetrodes and the IMD figures for the amplifier. Here was his response in an email.  I'm sure that he won't mind me posting it here for clarification purposes...

Quote
Hello Ian,

In various Russian sources for power dissipation (not output power) two figures are given - 600 and 800W. Although this is not specified, it is likely that long-term military service is considered. However, when defining the power of ham-radio amplifier we are using ICAS (Intermittent Commercial and Amateur Service).  When Alpin 100 producing 1 KW Output , the power dissipation is about 530 W !!! Of course, to achieve maximum power, adequate cooling is needed as well as adequate sources for the Plate and grids.

When I presented this amplifier in Friedrichshafen exhibition, several russians came to the booth and said they did not believe that this tube GU-74B can produce 1KW output. Then I showed them that I use for the demonstration HP wattmeter and Bird Dummy Load, after which I activated the amplifier and it produced more than 1 KW out. The visitors in question said they believed in the measuring equipment but still did not believe that GU-74B can produce 1 KW out !!!
It should be noted that almost all Russian tubes have large differences in parameters. Some brand new pieces GU-74B can produce only 500-600W and other twice more. I use very well selected tubes.

Merry Christmas for you and your family

Veselin lz1hd

Although he didn't specifically address the IMD figures issue, however I would refer you back to my previous post with regards to the reviews of RadCom, etc. where the IMD figures are addressed in their tests...


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KX2T on December 15, 2017, 09:30:25 AM
Well the expert has said it all, his hearsay has totally sunk any Russian tubes from being used, this is just like the BS we get on TV about politics but twice as bad. We should all sell our amps which use Russian tubes or throw them in the trash right now cause KM1H said soo, please give me a frigging break, BTW there at this time are almost as many Acom amp's in many ham shacks world wide Karl as Alpha's amp's. You seem to have a bone to pic cause of the cold war stigma from the 50-60ies but many here look at what you are saying as hearsay cause you dont like any of these Bulgarian built amp's. Acom started after Alpha pulled the contract on the 91B amp but still they produced the 99 for many years but to be honest the 99 was way overpriced and did not sell as well as the Bulgarian 91B did.
In over 40 years I have owned many different amps like SB200,SB220,MLA2500, HB8877,AMP supply LK500Z,Ameritron AL80B, ALS1300,AL1200,AL1500,QRO1000 then Alpha's 78,77DX,91B and this little Acom1000, the least trouble free with zero failures were the QRO1000, the AL1500, Alphas 78&77DX, the Bulgarian Alpha 91B and the Acom 1000.  I had the use of Alpha 87A's and Acom 2000A's when we used to have a contest station back in 1990ies also which btw the Acom 2000 with those Russian tubes cleaned the Alphas 87A clock. As far as raw output the HB8877 was king of the hill, the 77DX was next and the 91B was right behind it then the AL1500 but to be honest I never trusted the Ameritron amps in contest station as much as I trusted the 91b. I think what you have been hearing about the Russian tubes is they had a heavy duty transformer that Acom and Alpha sold to be used with there amp's that some how got into some production samples which was designed for CCS RTTY use but also placed much higher plate voltage on those tubes which is like if you give a kid a hi power new toy he is going to use it, end results those tubes were putting out just over 3Kw and 2.6K was there limit but you should know how hams work by now. You run any amp hard you will find its breaking point but at 1500W out now way and for a single GU74B running 900-1000 out is far better than running an AL80B at 1KW out.
As far as the bull crap as far as your hearsay Karl, the newer GU74B's with the 2017 date code are newer tubes, there base before the cooling anode is higher like what Eimac did in the 3CPX800A7's and they are silver plated like the Eimac's so you BS about changing date codes is far from the truth, there is new stock GU74B tubes to be had and Svetlana tubes are still in production but at a higher cost but in no way are the prices as hi as Eimacs rip off's.
As far as the Chinese knock off tubes they have not learned how to build there tubes with best quality grid structures and this has been documented on the internet, just google it OM.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KM1H on December 15, 2017, 02:45:57 PM
Quote
I just talked to a Broadcast Engineer who mentioned having to start up high power tubes S-L-O-W-L-Y to keep heater current down during cold startup.

Yes, some tubes with handles or needing a hoist to lift fall into that category BUT "typical" ham tubes up to the 3CX10000A7 are instant on. At the 3CX15000/20000A7 level the warmup is 5 seconds ;D :o ::)
Tetrodes are similar being instant on to the 4CX15000 and the 4CX20000 requirement has a requirement to limit instant on current to 2X rated and this can be done with intelligent transformer design.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KM1H on December 15, 2017, 03:10:39 PM
Quote
Well the expert has said it all, his hearsay has totally sunk any Russian tubes from being used, this is just like the BS we get on TV about politics but twice as bad.

Your reading comprehension is at the grammar school level, I suggest you get professional remedial training.

Quote
As far as the bull crap as far as your hearsay Karl, the newer GU74B's with the 2017 date code are newer tubes, there base before the cooling anode is higher like what Eimac did in the 3CPX800A7's and they are silver plated like the Eimac's so you BS about changing date codes is far from the truth, there is new stock GU74B tubes to be had and Svetlana tubes are still in production but at a higher cost but in no way are the prices as hi as Eimacs rip off's.

Provide a factory link to all that and I may believe you about new production. My #2 sons GF is from St Petersburg and they will be there in early January and have volunteered to contact the factory. He speaks Russian like a native and has a MSEE degree.
As far as the 4CX800A, the tube was washed of the GU-74B labeling and fraudulently relabeled; Ive seen several but cant claim all were that way once Baxter got caught.

The Svetlana engineers report is not hersay as you would love to believe and I never claimed a pair of GU-74B's were bad at 1500W. You really need that remedial course. And you should stick to subjects you actually know.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KM1H on December 15, 2017, 03:30:57 PM



Quote
Although he didn't specifically address the IMD figures issue, however I would refer you back to my previous post with regards to the reviews of RadCom, etc. where the IMD figures are addressed in their tests...

I wonder why? IMD is a touchy subject and is easily nanipulated

Quote
I looked at other manufacturer's claimed figures, like Ameritron using Eimac valves, OM Power and Acom using Russian tubes. They all  quote nearly the same IMD figures, give or take a few dB.

Eimac uses the long accepted IMD measurement method of reference to a single tone and is what the military and other professional users measure against.

The Hammy Hambone ARRL uses the PEP method which is an automatic 6dB improvement and they also cherry pick the two tones which can further improve the IMD3 reading; Radcom apparently does the same as do others trying to inflate the results.
The subject has been discussed in detail on here or/and QRZ.

Carl


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KX2T on December 15, 2017, 05:33:45 PM
Karl you are the self proclaimed expert so why should any other ham try and give there opinion on these forum's, everyone else is wrong and you are right plus you want to pick on the ARRL lab and Radcom as well. What is funny is I have never seen any of your reviews in any ham magazine, zero, nada, not even CQ magazine.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KM1H on December 15, 2017, 05:55:51 PM
Quote
Karl you are the self proclaimed expert so why should any other ham try and give there opinion on these forum's, everyone else is wrong and you are right plus you want to pick on the ARRL lab and Radcom as well. What is funny is I have never seen any of your reviews in any ham magazine, zero, nada, not even CQ magazine.

It appears that your reading ability is on a par with comprehension Jimmy. Plus you have such a low technical ability you dont even understand the basics about IMD and how they are manipulated to keep advertisers happy.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: VK3BL on December 15, 2017, 08:02:16 PM
Personality aside, Carl's history lesson is correct.

The 3CX800A7 is a better tube than the GU-74B "4CX800" in every single way.  Yes, it costs more, but its still made, and is one of the most linear "small" power tubes ever produced.

The bias requirements alone should be enough to scare people away from the GU-74B; ~500 Watts of heat just to keep it linear, in a tube officially rated at 600 Watts Plate Dissipation.  Those numbers simply don't add up.

Combine that with uncertain future production runs (more unlikely than likely), and its easy to understand why those who have read up on the matter are less enthusiastic about that particular tube.

If you must have a tube amp in this day and age, and the price of the 3CX800A7 or 3CX1500A7/8877 scares you off, your best bet is the FU-728F, although it tends to be pushed pretty hard in Ham amps too, but thats the nature of the game I suppose.  At least most amp vendors allow you to swap in a 4CX1500B (with reduced power output) and you can expect in return a very linear tetrode based amp.





Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KOP on December 16, 2017, 12:34:52 AM

The subject has been discussed in detail on here or/and QRZ.

Carl

Isn't that the truth

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


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: MM0IMC 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?  ??? That's somewhat rhetorical, as I've a lot of money invested in it.  I wish I hadn't asked the original question now... :-\

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!


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: G3RZP 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.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: VK3BL 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?  ??? That's somewhat rhetorical, as I've a lot of money invested in it.  I wish I hadn't asked the original question now... :-\

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 :)  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 :)

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 (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.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KX2T 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.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: MM0IMC 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!  :D

Somebody said that Europeans are "cheaper", well I resemble that remark!  ;D 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.  :o


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KM1H 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



Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: K6BRN 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.  :)


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KM1H 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


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KA5COI 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.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: G3RZP 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.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: W1VT 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


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KM1H 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


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: MM0IMC 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. ;D


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: AE5GT 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.







Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: MM0IMC 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. ??? I'm sure somebody will be along in a minute and enlighten me. ;D


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: K6AER on December 17, 2017, 03:09:00 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.







To a Blacksmith it is call tempering.

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


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: MM0IMC on December 17, 2017, 03:33:42 PM
I thought it was named after two people, like the Something Something effect? ???


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: N2MG on December 17, 2017, 04:28:17 PM
"Work hardening" comes to mind.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: VK3BL on December 17, 2017, 04:50:46 PM
"Work hardening" comes to mind.

Agreed, although not analogous in this case because you'll also get annealing from the heating/cooling of the filament.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: VK3BL on December 17, 2017, 04:52:10 PM
I thought it was named after two people, like the Something Something effect? ???

Yup, name eludes me too.  But you're right, its mentioned in care and feeding...


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: N8FVJ on December 17, 2017, 06:05:52 PM
New manufacture indirect heater tubes are expensive and are not dependable. I simply use older manufacture 572Bs. They last years & years and are not too expensive. Also are instant on, no warm up delay


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: MM0IMC on December 18, 2017, 02:58:37 AM
I'll stick with my present amplifier and just turn it on when needed. Most of the time, it just sits there turned off at the switch at the back, gathering dust - till it's needed. ;)  I helps keep my desk from floating away, if we ever lose gravity in my part of the world! :D

I run it with the Yaesu FT-450AT with the lowest possible microphone gain (no compression) and with 24W input, it'll do just under the 400W PEP legal limit here in the UK, all day long if required.  When using RTTY or SSTV, I always run it with absolutely no ALC showing on the rig's meter. This gives me around 250W-300W output on SSTV.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: AE5GT on December 18, 2017, 06:49:29 AM
I m thinking more along the lines of metal fatigue.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: VK3BL on December 22, 2017, 12:56:57 AM
I m thinking more along the lines of metal fatigue.

There is a specific transition temperate that filaments go through that causes most of the damage, its credited to the people that discovered it, and its distinct from fatigue, work hardening or annealing.

Its called the 'Miller-Larson' effect.

Its the reason vacuum tubes make use of springs to support the filaments; basically, its a transition temperature in which the filament metal goes through a 'plastic' state, resulting in grain reorientation and lengthening (and the associated thinning).

You can read about it here:
https://books.google.com.au/books?id=RuDj_oiKl9wC&pg=PA498&lpg=PA498&dq=tube+filament+standby+voltage+dark&source=bl&ots=bsDfuGF43_&sig=-Ax0P27XtAfHa9RKvtxX40SGkZM&hl=en&sa=X&ved=0ahUKEwjPn9u4n53YAhUHmJQKHRzhD3kQ6AEIPTAG#v=onepage&q=tube%20filament%20standby%20voltage%20dark&f=false (https://books.google.com.au/books?id=RuDj_oiKl9wC&pg=PA498&lpg=PA498&dq=tube+filament+standby+voltage+dark&source=bl&ots=bsDfuGF43_&sig=-Ax0P27XtAfHa9RKvtxX40SGkZM&hl=en&sa=X&ved=0ahUKEwjPn9u4n53YAhUHmJQKHRzhD3kQ6AEIPTAG#v=onepage&q=tube%20filament%20standby%20voltage%20dark&f=false)


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: MM0IMC on December 22, 2017, 12:59:45 AM

There is a specific transition temperate that filaments go through that causes most of the damage, its credited to the people that discovered it, and its distinct from fatigue, work hardening or annealing.

Its called the 'Miller-Larson' effect.


Thanks, that's the one I was thinking about, but couldn't remember the name. :)


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: VK3BL on December 22, 2017, 01:01:51 AM
Thanks, that's the one I was thinking about, but couldn't remember the name. :)

Your welcome :)

I knew it was Miller-something, but it eluded me for some time until I realised I'd read it in association with reduced 'standby voltages' and 'black heat'.

I couldn't just google 'Miller Effect', as Mr. Miller was somewhat prolific in his discoveries, e.g. the Miller Capacitance.

In the end, Google then took care of the rest :)


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: VK3BL on December 22, 2017, 01:12:09 AM
New manufacture indirect heater tubes are expensive and are not dependable. I simply use older manufacture 572Bs. They last years & years and are not too expensive. Also are instant on, no warm up delay

To be frank, I'm utterly sure you're not well read enough to make such claims.

Certainly, I cannot imagine the 3CPX800A7 and 3CPX1500A7/8877 tubes would have seen such widespread usage in medical applications if a couple of 572Bs (a tube that even when first made was begging for a use) would have sufficed; offering better reliability and lifetime.

I've encouraged you previously to read more; I understand if there is a specific reason this cannot be achieved, but if that is indeed the case, please don't pollute these forums with ridiculous claims.

In another thread recent thread (the AL-572 one) you misquoted someone else as saying 572Bs are rated as 10,000 hours.  When I responded to that person stating that their claim was ludicrous, they politely pointed out they never made such a statement.  I then checked the thread, and they indeed had not.

Whilst I bear some responsibility for not fact checking before posting, your actions directly lead to me having to sincerely apologise to another member of these forums.  I did not appreciate having to do that, and having been made a fool of.

Simply put, that is unacceptable; and a complete violation of the Ham ethos of self education and helping one another.

At this point - in the interests of the community - I am obliged to recommend others question your statements and advice, lest they appear foolish or do something stupid and potentially dangerous.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: W8JX on December 22, 2017, 03:08:03 AM
Certainly, I cannot imagine the 3CPX800A7 and 3CPX1500A7/8877 tubes would have seen such widespread usage in medical applications if a couple of 572Bs (a tube that even when first made was begging for a use) would have sufficed; offering better reliability and lifetime.

I have little doubt that reason they use the ceramic valves is because of higher power output, more compact design, more rugged in handling/replacing, ducted cooling that allows tube heat to be discharged outside of unit without heating chassis, frequency range of tube and list goes on. I seriously doubt that filament life is part of choice logic because in medical use they swap them long before they get close to rated life. Operating parameters are the determining factor here.


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KM1H on December 22, 2017, 02:26:38 PM
External anode tubes also cost more, with Eimacs especially as there is about a 2:1 price difference between and Eimac provided tooling/training to the Chinese, but allow "serious" power without the frequency limitations of a huge glass tube. The 3-500G seems to be the current glass tube transition point of cost per Watt. The 2000T was about the largest of the 30's designed internal anode triodes and was maxed out at a measly 5400W in AM service. ;D

Lack of new products has rendered tubes such as the 3-1000Z and 4-1000A to the expensive low volume replacement market, new old stock, Fleabay, and hamfests.

Carl


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: VK3BL on December 24, 2017, 08:11:30 PM
Certainly, I cannot imagine the 3CPX800A7 and 3CPX1500A7/8877 tubes would have seen such widespread usage in medical applications if a couple of 572Bs (a tube that even when first made was begging for a use) would have sufficed; offering better reliability and lifetime.

I have little doubt that reason they use the ceramic valves is because of higher power output, more compact design, more rugged in handling/replacing, ducted cooling that allows tube heat to be discharged outside of unit without heating chassis, frequency range of tube and list goes on. I seriously doubt that filament life is part of choice logic because in medical use they swap them long before they get close to rated life. Operating parameters are the determining factor here.

So let me get this straight; you're suggesting that a tube with:
A more compact design
More rugged in handling
Better cooling
And a list that goes on

Is going to have worse filament life than a poor QC control 811A.  Have you even seen the photos of the Shu Guang plant and the complete lack of cleanliness?

Irrespective, "filament life" is not the issue, internet element poisoning due to poor manufacturing standards and materials is.

Just ask Carl (or any other amp repairer) how many ceramic tubes he's replaced over the years compared to glass envelop tubes.  There simply is no lifetime comparison.

For one, more compact = less gas = less potential for filament poisoning.

CT / MRI machines are left on 24/7, do you REALLY think they replace tubes every 1500-3000 hours?!  Of course lifetime is a design consideration!!!!!!



Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: MM0IMC on December 25, 2017, 02:40:43 AM
But you get a nicer glow from a glass valve. ;D


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: W8JX on December 25, 2017, 05:41:44 AM

So let me get this straight; you're suggesting that a tube with:
A more compact design
More rugged in handling
Better cooling
And a list that goes on

Is going to have worse filament life than a poor QC control 811A.  Have you even seen the photos of the Shu Guang plant and the complete lack of cleanliness?


Exactly where did I say a ceramic power tube has worse filament life than tube you mention?


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KM1H on December 25, 2017, 09:54:02 AM
Quote
Just ask Carl (or any other amp repairer) how many ceramic tubes he's replaced over the years compared to glass envelop tubes.  There simply is no lifetime comparison.

Very few and after the RCA 8122 fiasco was fixed. All were owner admitted faults to the 8873/74/75 family, 8877, and 3CX800A7's without any or adequate fault tolerance circuits. I will not work on amps with Russian tubes which are run well out of design and have a short emission life or short first.

Carl


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KM1H on December 25, 2017, 03:16:13 PM
Quote
But you get a nicer glow from a glass valve.

Not when it is in a cabinet and whatever airholes there are are not situated for easy viewing; exceptions are when chimneys are used such as the L4/4B and AL-82 and other amps with easy viewing holes.

Because of the way they are setup here I see nothing glowing and have to lift the top cover of vintage RX, and TX (most are all screwed together cabinets) to see anything.....even a 807!

Carl


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: N2EY on December 26, 2017, 08:22:54 AM
I have little doubt that reason they use the ceramic valves is because of higher power output, more compact design, more rugged in handling/replacing, ducted cooling that allows tube heat to be discharged outside of unit without heating chassis, frequency range of tube and list goes on. I seriously doubt that filament life is part of choice logic because in medical use they swap them long before they get close to rated life. Operating parameters are the determining factor here.

One of which is heater/filament life!

An MRI machine costs big bucks; tube cost is a drop in the bucket. For many hams, tube cost is a considerable factor. Preventive-maintenance replacement of tubes is just common sense when a failure in-service can be much more costly than the replacement cost.

Also remember: Warmup time. Many ceramic-metal tubes have indirectly heated cathodes and strict warmup-time rules. Eimac data sheet says 3 MINUTES for the 3CX800A7 and 60 seconds for the 8873 family. RCA says 60 seconds for the 8122 family. More time is better, too.

The NCL-2000 and the SR-2000 used a pair of 8122s - and both had time-delay circuits built in to prevent too-early application of B+ and/or drive. A different situation from the "instant on" directly-heated bottles.



Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KM1H on December 26, 2017, 03:09:33 PM
The MRI developed YC-156 is 5 minutes and most ham users of those pulls suggest 6 minutes.
Even so they seem to loose emission rapidly even run within specs.

OTOH it is an extremely easy tube to use, no socket required and a low power filament transformer is used.

Carl


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: VK3BL on December 28, 2017, 05:29:21 AM
The MRI developed YC-156 is 5 minutes and most ham users of those pulls suggest 6 minutes.
Even so they seem to loose emission rapidly even run within specs.

OTOH it is an extremely easy tube to use, no socket required and a low power filament transformer is used.

Carl

I didn't realise the YC-156 / 3CX5000A7 lost emission quickly... perhaps its because the pulls have reached their useful life?  Thoughts?


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: N9AOP on December 28, 2017, 08:54:43 AM
0IMC, Roger on the 'glow of the glass'.  But if your ceramic glows you may have a problem.
Art


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: AA2UK on December 28, 2017, 09:06:50 AM
Quote
Just ask Carl (or any other amp repairer) how many ceramic tubes he's replaced over the years compared to glass envelop tubes.  There simply is no lifetime comparison.

Very few and after the RCA 8122 fiasco was fixed. All were owner admitted faults to the 8873/74/75 family, 8877, and 3CX800A7's without any or adequate fault tolerance circuits. I will not work on amps with Russian tubes which are run well out of design and have a short emission life or short first.

Carl
Is there a Russian replacement for the 8874?
Bill, AA2UK


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: W8JX on December 28, 2017, 09:15:59 AM
Is there a Russian replacement for the 8874?
Bill, AA2UK

http://www.g8wrb.org/data/Svetlana/pdf/3CX400A7.pdf (http://www.g8wrb.org/data/Svetlana/pdf/3CX400A7.pdf)


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: MM0IMC on December 28, 2017, 09:24:41 AM
0IMC, Roger on the 'glow of the glass'.  But if your ceramic glows you may have a problem.
Art

I hope it doesn't glow!  :o  Here's a GS31B Russian triode with just the heater voltage applied. ;)

(https://s3.amazonaws.com/files.qrz.com/c/mm0imc/DSC_0996.JPG)

(https://s3.amazonaws.com/files.qrz.com/c/mm0imc/DSC_0997.JPG)


Title: RE: Indirectly Heated Valve (Tube) Longevity Question.
Post by: KM1H on December 28, 2017, 09:42:04 AM
Quote
I didn't realise the YC-156 / 3CX5000A7 lost emission quickly... perhaps its because the pulls have reached their useful life?  Thoughts?

Since most were in MRI's those are pulled on an filament on basis and were still full power.

I suspect hams were running out of tolerance filament voltage, exceeding grid current or some other parameter. Another reason was buying already beat up tubes from other sources or hams and CBers.

The YC-156 has a 3CX5000A7 anode and 3CX15000B7 internals
http://www.wv7u.com/yc156amp/qa/qa.html

Carl