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Author Topic: Defective Chinese 572b's out of 811h  (Read 4315 times)
KF5AHV
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« on: August 11, 2010, 12:55:28 PM »

http://s790.photobucket.com/albums/yy190/kf5ahv/

here are 3 pictures of a set of Taylor 572b's. i noticed a low output on the amp and took the tubes out to inspect them and noticed this. the tubes were bought last year in September.

 
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WB2WIK
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« Reply #1 on: August 11, 2010, 03:56:58 PM »

Did you try soldering that one?
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KF5AHV
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« Reply #2 on: August 11, 2010, 04:13:33 PM »

i did not. i pulled the tubes last night and seen this one was like this. i was noticing a little lower than normal output on the amp so i decided to pull a swap with some other tubes i have. the output returned back to normal. these still have about 6 weeks left unnder warranty.
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WB2WIK
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« Reply #3 on: August 11, 2010, 05:55:19 PM »

Looks like the tube anode got so hot it reflowed the solder.

Incredibly, this isn't so unusual and has been happening with similar tubes for decades.  I've found re-soldering them usually works fine.

Since the "world" went "lead free" a few years ago due to RoHS requirements, the solders used today should actually reflow at higher temperatures than previously, but they're not as good in some ways.
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N3OQD
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« Reply #4 on: August 12, 2010, 09:49:22 AM »

I contacted k5svc of whom sells tubes on ebay.  He sells the Svetlana's because of the high failure rate of the Chinese ones.  He says:  bought out the last remaining Svetlana 572 stock from the distributor last month. In the last two and a half years, I have sold over 2000 of the Svetlana 572B tubes and have had less than a dozen returns. Tere will be no more of the Svetlana tubes made and when my inventory is gone, the Chinese crap is all that will be available.
Frank K5SVC
Copy and pasted with his permission.
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N3LCW
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Posts: 133




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« Reply #5 on: August 12, 2010, 03:09:45 PM »

If you try resoldering the cap let us know if power returns to normal if you swap them back in.

Thanks.

Andrew
N3LCW
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N3LCW
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Posts: 133




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« Reply #6 on: August 13, 2010, 05:58:11 PM »

What modes and how much power have you been running the past year?

Andrew
N3LCW


http://s790.photobucket.com/albums/yy190/kf5ahv/

here are 3 pictures of a set of Taylor 572b's. i noticed a low output on the amp and took the tubes out to inspect them and noticed this. the tubes were bought last year in September.

 
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K9RLB
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Posts: 17




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« Reply #7 on: August 18, 2010, 10:24:29 AM »

Why were 572b tubes in an AL-811H? The amplifier was designed for 811a tubes. No wonder people have such a high failure rate! I have to wander if tube warrenties cover tubes installed in amps they are not designed for.
I had mentioned this on another post - and I will repeat here:
"With a 572B - it will always be mistuned in an AL-811(lack of plate voltage for a 572b. Also, there are circuit differences in the amps constructed to run 572B's and the amps constructed to run 811's.
All the 572B amps have a grid leak resistor in the control grid circuit to provide "self bias' for the tube.
The 811 circuit has the control grid grounded, so if a 572B tube is put in that circuit without the proper modifications done for the grid leak resistors then that tube (the 572B) Is gonna draw more current than it should and it's gonna draw current when it shouldn't.
I'd get a new set of 811a's, and take the money I saved and buy a 3898 tuning aid! That will make the tubes last longer.
Otherwise, plan on new 572b's at least every year or so."

If you like 572b's, use an amplifier designed for them, and you'll have a lower failure rate, and save money on buying replacements.
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N3OQD
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« Reply #8 on: August 18, 2010, 02:46:22 PM »

Quote: Why were 572b tubes in an AL-811H?  Well Ameritron two years ago said to me on the phone that they recommend the upgrade.  They even had a limited run of the model AL-811HD that came from their factory with 572b's stock.  Yes there are slightly different plate and load positions BUT essentially these tubes work just the same. The benifits are better plate disapation for longwindedness (LOL), MODESTLY longer AM and RTTY duty cycle and most importantly (for me) more forgiving of mistunes (senior moments).  This provided that the tube factory has had a good QC day.  For what it is worth, the failure rates of this tube are directly due to the quailty control at the Shugang tube factory in China.  Tom (the designer of the Ameritron amps) has been been banging his proverbial fist on the table to get this issue addressed over there.  This is the actual cause of premature tube failures many hams have been experiencing of recent.
« Last Edit: August 18, 2010, 02:57:24 PM by Charles P Hayloe » Logged
K9RLB
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Posts: 17




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« Reply #9 on: August 18, 2010, 09:56:35 PM »

N3OQD:
You didn't address the circuit differences.
Are you implying a 572b doesn't need grid leak resistor to self bias the tube? If so, why do other amplifiers designed for 572b's have them, and those designed for 811a's do not. Find a schemetic to a Yaesu FL-2100 / Heathkit SB200 / Ameritron AL-572 and compare the circuits to an AL-811 / 811H . . . They are different, because the tubes, although similar, are different. Why would Ameritron be using 811a and suggesting 572b's in an amplifier not designed for them? Maybe because they sell 572b's and wanted to make a sale?
If Ameritron recommends this "upgrade" even though it is a waste of money, they should publish it.....along with the proper mod.
China has been making tubes for many, many years. Everyone seems to love the China tubes when RF Parts silk screens TAYLOR on them. Same factory, same tubes. Maybe Ameritron should silk screen an American sounding name on theirs, they would probably last longer / work better / more output / and be more rugged! No matter what they do, if the circuit is not modified, it is wrong - and the tubes will fail, and that will be the fault of the user, as the amp is made for 811a tubes.
Oh, I left out the "run cooler" aspect. I bet they do, I bet they run so cool in an 811 amp, the getter does not heat up enough to keep the air out. With the plate voltage designed to be linear for an 811a tube, and not so linear for a 572 due to lack of plate voltage, I would put my bet on the 811a working better anyway. Cheaper / better for the application.
If you want an AL-572, buy an AL-572......don't buy an AL-811H and try to make it something it isn't.
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K9RLB
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« Reply #10 on: August 18, 2010, 10:05:44 PM »

 They even had a limited run of the model AL-811HD that came from their factory with 572b's stock.  
Limited run? They are still advertising them as for sale / in production. They are $300 higher. That $300 difference should be more than the difference between the 811a / 572b tubes. I would bet thet 811HD is set up for 572b's, and they aren't just stuck into the 811a's circuit...or, I would hope so. Hard to tell about Ameritron / MFJ -
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N3OQD
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Posts: 104




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« Reply #11 on: August 19, 2010, 08:12:38 PM »

I understand what you are addressing in "circuit differences".  But the reality is that I have been running the 572B's in my AL-811 for about 3 years with no problems.  Just to see, I pulled out the original 811a's and carefully tried to see the differences in performance.  Asside from the slightly different positions of the plate and load caps, they pretty much worked the same.  Predictably, power output is limited by plate voltage to the amplifier's stock 600w.  In practice, not much difference exept you have plates with much more mass (graphite) versus thin tin of the 811a's.  In other forums even the guy that actually designed this amp in the first place, recommends this upgrade himself.  RF parts says that the 572 is a plug and play upgrade from the 811 also.  Countless other hams have also done this upgrade sucessfully (provided they get decent QC made tubes).   You mention that the 572's don't get hot enough to getter.  (asside from the NOS Svetlana's) all 572b tubes are flash barium gettered at the base just like the 811a.   Bright silver patch is pretty much indicative of a good vacume.  So in retrospect, I understand (for this application) circuit theory versus real life application.  Many times theory wins out but on a rare occasion, real life performance can be quite different.  Mathmatically the bumble bee should not be able to fly.  Mathmatically the original Harley Davidson V twin engine should not run.  In both cases real life wins out.  If Ameritron themselves recommend the upgrade AND this does not void warrentee, they obviously know this works.  As the saying goes, "If it aint broke, don't fix it".  PS" tell me how the Dentron QRO and Dentron Clipperton L are grid biased on THEIR 572b's.  You just might find that there is more than one way to circuit a grid (LOL)
« Last Edit: August 19, 2010, 08:55:53 PM by Charles P Hayloe » Logged
N6PJB
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Posts: 5




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« Reply #12 on: August 20, 2010, 09:42:57 AM »

Tom, W8JI, says they are OK to use, therefore they are good to use. He's the MAN!
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