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Author Topic: 811a scorch marks  (Read 2776 times)
K3GC
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Posts: 11




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« on: December 24, 2009, 07:13:13 AM »

First off and this will become abundantly obvious. I am a newbie to amplifiers.
I have an Ameritron 811 which is working quite nicely despite some early errors.  Once or twice I flipped it on while it was tuned to another band.  Quickly changed, retuned, and no apparent damage (I guess this is one of the great advantages of tubes).
This morning I took the cover off to do an inspection of the inside of the amp.  All looks well except for the tube next to the transformer.  The side adjacent to the transformer is blackened.  The amplifier still tunes normally and puts out full power (I never load it for more than 500 watts.
Should I be concerned about this one tube or all the tubes?  If the verdict is that the one tube is about to die should I just replace that tube or should I replace all three?
Thanks
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KD8GEH
Member

Posts: 620




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« Reply #1 on: December 24, 2009, 07:52:19 AM »

Hi Gene and welcome to the hobby.

Just a few tips:  Always post your call sign, most ops wont respond to anon posts. Secondly, clearly detail the amp model and bands your loading etc.

If you do that, I could help you.

73,  Dave KD8GEH
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K3GC
Member

Posts: 11




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« Reply #2 on: December 24, 2009, 08:37:50 AM »

Sorry 'bout that.  The call is KJ4QFU.  The problem as stated (if it is indeed a problem) would occur on all bands.  I basically operate on 40 and 20 meters.
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KD8GEH
Member

Posts: 620




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« Reply #3 on: December 24, 2009, 12:24:10 PM »

You sometimes see that on tubes from overheating the grid from miss tuning the amp. Is it an Ameritron amp, like an 811H or something similar? As far as replacing the tube, if its that type of amp, you can usually get by with one. Older amps usually require matched sets for equal nuteralzation. Without some trouble-shooting, its hard to tell if it is really a problem. I keep a spare set on hand to reduce down time. (about 20 bucks each) Dont tune more than 10 secs at a time, allow the tube to rest until you have it tuned properly.

Hope this helps.

73 and merry c-mas
Dave KD8GEH
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K3GC
Member

Posts: 11




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« Reply #4 on: December 24, 2009, 01:51:25 PM »

Thanks for the reply.  It is an Ameritron AL-811.
It would certainly seem prudent to order a replacement set of tubes though  the amp is working with no apparent problems.  I notice that RF parts sells a matched set of 811a for about $63. Is this worth it?
Gene KJ4QFU
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KH6AQ
Member

Posts: 7982




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« Reply #5 on: December 24, 2009, 04:21:32 PM »

I also bought a matched set from RF parts for my Ameritron 811 amp and they work just fine. If I'm not mistaken, W8JI says that matched sets are not required.
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KD8GEH
Member

Posts: 620




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« Reply #6 on: December 24, 2009, 05:55:20 PM »

True, matched sets arent required, but its a good thing.  I have an 811H, good design, and easy to work on. Use care not to over drive it and you should get many years of service.  
If you have an H you will need 4 tubes, 3 for the 811. Check the 51 ohm resistor on the grid circuit at the terminal strip connections at the left in front of the tubes, there are 4. If the tube shorted, it may go out and need replacement. Ameritron sells then for a few cent a piece.  RF parts or Ameritron are both good tube sources.
Hope to catch you on the air sometime.

73  Dave  KD8GEH
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AE5JU
Member

Posts: 244




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« Reply #7 on: December 31, 2009, 07:10:24 PM »

Gene, you might want to reregister using your call sign.

No need to replace all three tubes if just one is suspect (the blackened one).

But for a spare set, you might want to consider a trio of "811H" tubes from RF Parts.  To me, they seem to be a "best buy".

Paul
AE5JU
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K3GC
Member

Posts: 11




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« Reply #8 on: January 01, 2010, 10:02:58 AM »

i have been attempting to get my user name changed to my call but have been unable thus far to get a response from the webmaster.
Gene
KW4GC
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WD8SBB
Member

Posts: 33




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« Reply #9 on: January 04, 2010, 04:27:31 PM »

Not sure, but if things are really as they are suppose to be, then could it be you are looking at a getter flash deposit on the inside of the tube?  

Not sure what your tube's physical design is, but you are kind of describing what a getter fire spot looks like.
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K3GC
Member

Posts: 11




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« Reply #10 on: January 04, 2010, 05:02:22 PM »

I have not the slightest idea what you are talking about and Google was little help. If this is normal shouldn't it appear on all three tubes?  It is only on the one tube though. As I have said everything seems to be working normally.
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AE5JU
Member

Posts: 244




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« Reply #11 on: January 04, 2010, 05:54:47 PM »

Is it black or is it silvery?  Is it on the side near the little silver disk?
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K4DPK
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Posts: 1128


WWW

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« Reply #12 on: January 05, 2010, 12:50:31 PM »

The call you listed, according to the FCC data base, has been cancelled.

You shouldn't be operating with or without an amplifier.

Phil C. Sr.
k4dpk
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KD8GEH
Member

Posts: 620




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« Reply #13 on: January 05, 2010, 02:10:55 PM »

http://www.youtube.com/watch?v=3HKzU2bTmoo

I see 2 dirrerent calls...  anyhow here is a utube vide from Mike that gives the info on 811s.  73 all

Dave  KD8GEH
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KD8GEH
Member

Posts: 620




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« Reply #14 on: January 05, 2010, 02:15:33 PM »

IC congrats on the vanity call Gene!

73  Dave
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