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Author Topic: AL-80b low grid current/Power output  (Read 30405 times)
NC5T
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Posts: 44




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« Reply #45 on: November 27, 2014, 05:59:10 AM »

Good Morning and thanks once again for the replies and suggestions!

  Well, after a thorough cleaning and all of the troubleshooting so far, I ran all of the bands again and did not get enough of a difference to matter.  Most bands were less than a point away from the original results on the plate and load settings and the biggest change on the whole chart was 10M where grid is now showing 60 and I am getting 620w out.

  It varied by band, but the highest grid current with 100w was 70 and the power did come up a bit, but only 50-100w at most.  

  I also looked closely at the SWR on all bands and the worst were 17M at 3.2:1 and 10M at 2.2:1.  The rest of the bands, with 70w drive, are 1.2:1 to 1.7:1 and it increases slightly the more power I drive it with.  Just to see how this was effecting the output I put a tuner inline  between the amp and the radio and tuned them flat.  It didn't make enough of a difference to note so I decided not to mess with the tuning slugs for now.

  I did leave 17M out in the original as I don't really operate there much, and with the SWR, I figure the amp is definitely favoring 15M, which is fine with me as I operate there quite a bit.  

  With all of this said and done, I decided not to mess around any further and I have a new RF Parts 3-500ZG on its way.  I guess I will see if the tube is the problem in 3-5 business days and if not, at least I will have a spare when this one does go bad.

  I really appreciate all of the helpful suggestions and advice that have been provided.  I will follow up when I get the new tube.

73 and have a Happy Thanksgiving!!

Bob
NC5T
« Last Edit: November 27, 2014, 06:01:44 AM by NC5T » Logged
NC5T
Member

Posts: 44




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« Reply #46 on: December 05, 2014, 04:49:03 PM »

Good Evening,

  Just to follow up, I got my new tube today and wow, what a difference!  I ran the numbers again with 70W drive on the amp into a dummy load   Here are the numbers I am getting now with the new RF Parts 3-500ZG:
Band    Drive  Ig     Ip    Output  Plate   Load
10M    70w     110  450   775       9.5   7.75
15M    70w     150    450   900       9         5.5
20M    70w     120  425   1000       8.5   3.25
40M    70w     125    400   950       7.25   3.25
80M    70w     120    350   750       3.25   2.25
160M    70w     140  400   750       5.25   2.75

  Also, the SWR's were pretty much flat with the highest being 1.2:1 up on 15M, so I guess this took care of that issue somehow as well.

  I can now hit the advertised 1000W on all the bands now if I drive it a little harder, but I am really satisfied with the output now with 70W drive and from what I've read, keeping it there should help to keep the tube in good shape for years to come...hopefully! 

Thanks again for all of the help and suggestions!

73,

Bob
NC5T
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K4RVN
Member

Posts: 261




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« Reply #47 on: December 08, 2014, 01:17:02 PM »

Thanks for the update Bob as I have an AL 80 B and will note this problem. Looks like my vote in Reply # 36 was correct for the bad tube. Now enjoy your AL 80 B it is a great amp.

Frank
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N3DT
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Posts: 1655




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« Reply #48 on: December 13, 2014, 05:57:16 AM »

Yes, you're getting better efficiency than my 7 year old tube. I'm lucky to get 750 out on the higher bands, even if I jack up the HV which puts the filament E at 5.5, so I stick with the lower HV and the recommended jumpers on the transformer for 115VAC.
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K4RVN
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Posts: 261




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« Reply #49 on: December 13, 2014, 04:20:18 PM »

This is off the subject N3DT:
I really think you are over reacting to the filament voltage thing since both plate and filament come from the same transformer primary. Having owned the AL 80A for 25 years, I never measured my filament voltage. I own both the AL80A and AL80 B and operate them daily from 240 volts. I find the amps operate better on my 240 volt supply. My 20 amp dedicated 120 volt circuit had voltage drop when the amp was heavily loaded. This also affected the filament voltage. AS far as tubes are concerned my 17 year old Amperex made in France still does well but was replaced  several years ago with a 3-500C made in China. I would suggest you consider cranking the high voltage up to maximum as specified by Ameritron to prevent early failure from not running hot enough to getter  the 3-500. I followed your thread and thought you might benefit from my long experience with these amps. I do know the choice is yours so wanted to let you know that you may be hurting your tube.
73,

Frank
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W1QJ
Member

Posts: 2947




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« Reply #50 on: December 14, 2014, 06:41:50 AM »

The person who designed the amp prefers that you drive the amp to full rated output and check to see what the input swr is at that point.  If you can't obtain rated output from the amp that indicates another problem that may not be related to  adjusting the input.  Then by adjusting you may bei doing something that really should not be done.  If the amp is new I would doubt they need adjusting unless you are going for  a tweak on the warc bands.

Howdaya like that?  A bad tube.  When a tube starts going flat and looses emission, the input matching isn't right anymore.  One should note this.  When you see the input matching turning for the worst and the output falling. "think bad tube coming".
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N3DT
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Posts: 1655




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« Reply #51 on: December 14, 2014, 07:26:17 PM »

I do know the choice is yours so wanted to let you know that you may be hurting your tube.
73,

Frank

There seem to be 2 camps on this issue, HV set or filament set. I'm not an experienced amp designer or whatever, but I do run the tube to get it red sometimes. I can't say there's any difference in the operational responses I get or the quality of signal so far. I did run the HV up to 3100V no load (2700V full load) to the Ameritron instructions initially, and could really push the thing to 1KW on the lower bands, but found the PD on the higher bands was over spec as far as key down, but running SSB or CW probably doesn't matter much, then some say it's being run out of spec there too. I just don't know. I'm using a dedicated 30A 115VAC circuit (#10) to it and can't see any appreciable voltage drop that I know of. I could run it 220 and see what happens though, the HV droop during transmit may be better. It may be commercially it's one thing and amateur service another. I doubt in either case there's 1 dB difference on the other end. Looking at the book, it does specify half hour continuous carrier (RTTY) at 500W and CW continuous operation at 800W. I assume that's PO, but I still wouldn't run it key down at 500W PO unless the PD was reasonably under 500W, like JK says, that's with proper forced air cooling too. SSB or CW service is something else.  Thanks. Actually my tube is 10 years old, the amp was made in 04. Good thread.
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K4RVN
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Posts: 261




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« Reply #52 on: December 15, 2014, 01:03:24 PM »

With a supply using number 10 wire your amp should do just fine. A friend of mine runs his on 120 volts at 1100 watts. WB8 OTM, one of the best signals on 40 meters, but also has a great wire antenna array from Florida.

Frank
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N3DT
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Posts: 1655




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« Reply #53 on: December 15, 2014, 03:31:06 PM »

I thought about it a bit today and it's a toss up whether you want to abuse the tube with filament voltage or PD. Since I've reduced my HV to 2700 no load, the PD has become reasonable key down on the higher bands. But then are we abusing it in amateur service? I don't run RTTY or FM so it's a matter of if the tube is still operating in the linear mode in my book. I guess I need to get the scope out and look at the trapezoid patterns. Haven't done that yet, but it's in the plan. I guess the other thing is unless there's some scientific methodology on the two methods, I think it's a crap shoot. I wouldn't mind having the numbers that the guy that bought the new tube has though, mine is probably a bit soft from age, but I'm not complaining, I get 'big signal' reports from EU on 40 and 80 with dipoles at a decent height. I like the AL80B too because I don't have to upgrade my lightning suppressors and coax like I would if it were 1.5KW.
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