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Author Topic: Chinese tube manufacturing analysis  (Read 22448 times)
W8JI
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« on: September 16, 2011, 10:37:55 PM »

I had an interesting very long conversation with a tube manufacturing engineer who did a tear-down analysis of several Chinese tubes, and was involved in some visits to plants. It seems the major difference is in the USA, tubes are built (and were built) by a single worker doing all of one internal component, like a grid, all on fixtures dedicated to the job. Another employee does the next step. If one grid (or other element) is bad, all are generally bad. Either a step works and all elements are identical and passed on to the next stage, or none of them are good.

In China, at least according to him, multiple workers do the same job in parallel without much fixturing or high quality tooling. This results in a large  performance variation and much greater difficulty weeding out bad tubes.

According to him, a large part of the reason behind this method is to employ as many people as possible. The USA goal is to use the fewest people, for obvious reasons.

If this is true, this explains a great deal.
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AB1KC
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« Reply #1 on: September 17, 2011, 04:20:41 AM »

Your timing with this post is interesting Tom.

I am waiting for a replacement tube for my Alpha 9500 and I have expressed my concern about the use of a Chinese tube from the moment I learned that is what this amp came with. I even asked if it wouldn't be wise to "upgrade" to an actual Eimac built tube and I was told "No! we have more issues with the US made tubes..."

To be fair, I am not sure if the tube is the cause of my particular issue but it seems as though this is an easy first guess. If it is the fault, would you buy an Eimac over the less expensive Chinese tube?

The amp is almost two years old and it has pretty light use (6 months a year 2 hours or so an evening on 80 and 160, some weekend use on 20M etc. The "issue" is a loss of output after the amp heats up. When first turned on I will get 1500 Watts out from 35 Watts input for about 5 minutes, then it just fades away..... .No faults, warnings, smoke or anything else is happening, just  a loss of grid current then plate current along with output. Wait for a minute or too and everything works again but for less time.

We will see, I am expecting the tube today. If it is in fact a tube failure my gut says that in spite of what Alpha/RF Concepts say, I'd be happier with a US made tube.
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WA4NJY
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« Reply #2 on: September 17, 2011, 05:47:32 AM »


After reading all the bad news about new transmitting tubes, I am wondering how many NOS
6146's can be paralleled without problems.

Ed  Smiley
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AB4D
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« Reply #3 on: September 17, 2011, 06:49:34 AM »

Your timing with this post is interesting Tom.

I am waiting for a replacement tube for my Alpha 9500 and I have expressed my concern about the use of a Chinese tube from the moment I learned that is what this amp came with. I even asked if it wouldn't be wise to "upgrade" to an actual Eimac built tube and I was told "No! we have more issues with the US made tubes..."

The information you got from Alpha is fairly consistent with the information I received.  When I purchased a 9500 from Alpha, it was a sore spot of contention when I learned that Alpha had substituted a Chinese made Penta branded 8877 in my amplifier, in lieu of a Genuine Eimac, without my consent.  At the time, Alpha was pre RF Concepts, and they were advertising an Eimac tube as OEM.  I spoke to Molly about this, she indicated they had experienced a significant number of failures with Eimac tubes, and after changing to the Chinese made 8877, tube failures were almost non-existent.

I contacted Eimac about this claim, it was confirmed that Alpha had returned under warranty about 25% of the tubes from a bulk order.  The person I spoke with indicated after thoroughly examining each tube, there was evidence that at least some of the tubes had been pushed beyond Eimac's recommended limitations.  The remaining tubes were deemed faulty.  To settle things with Alpha, they did finally step up to the plate after some wrangling, providing a new spare Chinese 8877 that functions well.  I have no complaints about Alpha, they seem to stand behind their products.  So far, the original Chinese tube is still working well after three years, but my tube/amp has maybe 10 hours on it.  Time will tell.

73

     
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AB1KC
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« Reply #4 on: September 17, 2011, 07:16:59 AM »

I had a similar conversation with Molly when I saw the Chinese tube for the first time. My tube obviously didn't fare as well as yours has.
The new tube (Chinese) was delivered about an hour ago, it is in and running and it has passed the first tests with flying colors. I'll sit and use it today and see what develops.
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AB1KC
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« Reply #5 on: September 17, 2011, 07:21:21 AM »

Well,
I spoke too soon,
The amp is droping output still.
So much for simple quick solutions...
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K8AXW
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« Reply #6 on: September 17, 2011, 09:55:56 AM »

Well,
I spoke too soon,
The amp is droping output still.
So much for simple quick solutions...


To keep my mind as active as I can, I read all problems with amplifers here on Eham.com.  After reading your problem, I am somewhat confused.  Please forgive my ignorance.

What confuses me is the grid current dropping off..... if the drive remains steady.  Did you discuss this with Alpha?  Now with he second tube in place the same symptoms??? 

I hope you get this thing fixed yourself.... Alphas are like Cadillacs..... they're expensive to buy and expensive to fix..... simply because they're Cadillacs!
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A Pessimist is Never Disappointed!
W1QJ
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« Reply #7 on: September 17, 2011, 10:54:44 AM »

One question:  if you retune the amplifier after you notice power drop off will the power be restored with the same drive after a retuning?
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G3RZP
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« Reply #8 on: September 17, 2011, 11:16:14 AM »

AB1KC,

Does this happen on all bands? What happens to the input SWR when it happens?
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G3RZP
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« Reply #9 on: September 17, 2011, 11:18:19 AM »

Does this happen on all bands? What happens to the input SWR when it does happen?
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AB4D
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« Reply #10 on: September 17, 2011, 12:33:51 PM »

Well,
I spoke too soon,
The amp is droping output still.
So much for simple quick solutions...


Darn, sorry to hear the problem is still there.  First thing to do is to remove the antenna system out of the equation.  Do you have a dummy load that can handle the amplifier?  If the problem still exists, then check each band and antenna port, basically try eliminate the variables.  I haven't looked at the schematic, but is sounds as though something in the RF deck is going out of spec under load.

Make sure there are no bad solder joints.  I've read about a PA in a Kenwood hybrid behave in the same manner.   The radio's PA worked fine for many years, and then suddenly developed a problem similar to what you described. The cure, there was a component in the PA that was never soldered at the factory Shocked  Simply soldering the component fixed the issue.   

Let us know what you find.

73    
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AB1KC
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« Reply #11 on: September 17, 2011, 02:39:31 PM »

Well....
I walked away from the amp this morning frustrated.
Later I came back and decided to look again. I decided to plug it in and see if in fact it was still droping output. Warmed up the amp, selected the dummy load, began tuning with 10W drive, began increasing drive and "SMOKE"!

Now I know one part of the issue! It appears as though the RF Choke has burned up.

Looks like an easy replacement. What causes this failure?

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W1QJ
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« Reply #12 on: September 18, 2011, 05:56:51 AM »

I assume you mean the PLATE choke?  Plate chokes usually burn up when there is a resonance at or near the operating frequency.  Once the choke heats up and begins to arc between windings even on a band with no possible resonance the arcing will eventually cause the choke to smoke.  Finally the thin wire burns through and the choke opens.  There may be other causes.  You may want to investigate if this is a common problem with this amp and there may be a better upgraded choke you can get.
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K1LEM
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« Reply #13 on: September 18, 2011, 03:17:09 PM »

 Grin

After a heart to heart with two of RF parts testing, including Merrit, they agreed to accept my chinese tubes back and replace. However, sadly, of the four, the third one had a filament open! I have never had that happen before and wondered. if this was after shock from a nasty grid to filament gas arc?

Also changing grid current must be monitored with all three parameters watched. Grid current, plate current, VSWR.
The load conditions will shift if the RF load heats, is changing in reactance or in general is not resistive.
All such tests must be done into a dummy load in oil or in some medium that cools the load resistors.

I know this from my days as a filed engineer in broadcasting!
Also personal observation when the antenn gets wet.
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KM3F
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« Reply #14 on: September 18, 2011, 09:00:35 PM »

Some one has to find out if the tube is 'slumping', a term used when I was in that line of work.
A loss of grid current suggest the cathode is being poisoned and losing electron emission.
Certainly there will be a loss of plate current and RF output if this happens.
The usual way it goes is for the amplifier mfg er to point at the tube vendor and the tube vendor to point at the amplifier mfg er.
This is what happens with single supplyer situation when no one takes enough responseability to solve the issues.
It's called pi**ing in the snow.
An amp mfg er should be life testing samples on an ongoing basis to see what he is getting and see issues before to much public relations damage is done.
As far a China goes, is anyone surprised?
All they do is try to copy and then change the process to cost as little as possible and make junk to export.
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