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Author Topic: AL 80A How to tune an amp.  (Read 23980 times)
NO2A
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Posts: 1400




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« Reply #30 on: January 25, 2012, 12:11:28 PM »

Mark,I always stay right around 100ma grid current as reccomended. Most all of my operating is cw. On ssb it would be almost impossible to overdrive the amp with average or peaks.
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AD4U
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Posts: 2538




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« Reply #31 on: January 25, 2012, 01:29:01 PM »

FWIW.....Bill Orr always claimed that  most tubes used in a highly efficient amplifier design can be run at 2 times output of the plate dissipation.  Of course that would be a PEP rating.  I read that in the ARRL handbook.

None of us are doubting that statement.  What I still question is that EIMAC stated in writing on every data sheet that I ever saw that the MAXIMUM permissible plate current for a single 3-500Z tube was 400mA - period - no if's, and's, or but's.  That has nothing to do with the watts dissipated inside the tube.

What I still question is:

Whether a single 3-500Z can be driven to 500-550mA plate current and still produce a "clean" signal.

Show me where EIMAC put in writing that a single 3-500Z can be driven to 500-500mA plate current - as in the AL80 amp.

Dick  AD4U
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AD4U
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« Reply #32 on: January 25, 2012, 01:38:41 PM »

Hi.

So, is there a final decision on:

Max grid: CW and Phone

Max plate: CW and Phone

for the AL 80A?


Thanks so much for the overview. It reads like a history lesson and tech journal all in one.

73
Mark



EIMAC states specifically in ALL of the data sheets I ever saw that the 3-500Z tube can be driven to a maximum of 400mA plate current - period.  It does not matter the class of the amp, the duty cycle, the plate voltage, the power dissipated, the mode, the cooling, or the amp the tube is installed in........400mA is "IT".

Driving a 3-500Z to 500mA or 550mA, as in an AL80, is WAY beyond the PUBLISHED design limits for the tube.

In everything I ever read from EIMAC 400mA plate current per 3-500Z was "IT", no if's, no and's, and no but's.  If I am wrong (AND I HAVE BEEN WRONG MANY TIMES IN MY 63 YEARS) all I ask is somebody please show me a link to an official publication stating otherwise.

Dick  AD4U
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KC9TNH
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Posts: 304




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« Reply #33 on: January 25, 2012, 03:57:22 PM »

I've no test equipment & and not an engineer & don't play one on TV. I do listen to a few AL-80s from time to time whose owners do run the higher Ip under discussion with fine results as cited in a few of the posts. My only "IMD" benchmark is that they have very nice signals and (from checking) don't seem to splatter all over their neighbors.

I wonder how many problems attributed are not the result necessarily of exciter drive or the Ip run, but in not sufficiently LOADing the amplifier as part of the process. Amp-Rookie here, be gentle, just learning about this family of amp.
 Smiley
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73
Wes -KC9TNH
"Don't get treed by a chihuahua." - Pete
W1QJ
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Posts: 2948




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« Reply #34 on: January 26, 2012, 02:20:08 PM »

No doubt the spec sheet does say 400ma for maximum plate current.  On the other hand I think that would be a spec that would keep the tube happy and alive 24/7 key down.  In SSB service the same tube could probably be run at 500 to 550 and last just as long or longer than running 400ma in A0 modes.  Once you introduce IMD in the mix that is a different story.  We either discuss the health of the tube at a certain Ip or IMD at a certain Ip.  If the question was simply put like this....Can I run SSB at 500 to 550ma peak on my SB-1000 or AL-80A without blowing up the tube in short order?  The answer is yes.  If we ask the same question and add another variable of IMD vs 400ma the amswer is probably NO.  If you ran 400ma peak on SSB and that is all, the tube would hardly ever show much color.  Most of the time when any manufactuer spec's their product they spec it under the most severe duty.  Load rating on tires, rope, or just about anything.  They have to assume 100% duty cycle.  Other than a 100% duty cycle I am sure any rating on an item can be quite a bit higher on a short term basis.
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KK2DOG
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Posts: 35




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« Reply #35 on: January 28, 2012, 08:40:52 PM »

Get a "Pecker" and fugetaboudit.

     http://www.3898pecker.com/




       Mike KK2DOG
   www.hamwave.com
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NO2A
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Posts: 1400




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« Reply #36 on: January 31, 2012, 02:49:37 PM »

I have an old Ameritron brochure from 1992 that has specs for their amps. The AL-80A info says full load current 450ma. at 120v operation. No load hv 3000. Full load 2700.
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K4RVN
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Posts: 261




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« Reply #37 on: January 31, 2012, 04:48:16 PM »

Mark,
here is a link for the AL80A manual if you don't have one. After the cover sheet it reads:


http://blogimages.seniorennet.be/on4btw/attach/42175.pdf

Normal HV is 3100 volts no load, 2700 full load.
Average operating current is 400 MA max, 100 MA grid  on SSB. If you are seeing 400 MA plate current on SSB voice peaks, then you have mis-tuned the amp as it will not reach 400 MA on SSB at 1000 watts or under has been my experience. If your grid current is 200 MA on SSB, you have not properly tuned the amp. This assumes that you have a reasonable 50 ohm antenna or dummy load. I decided to heat up my tube today to possibly getter it. I used 75 watts drive on 12 meters to my antenna using around 1100 watts output on the external watt meter. The graphite tube turned red
on a long CQ into a mostly dead band. My Grid current was about 100 MA and Plate current less than 200 MA.
Having owned and used the AL80A for going on 23 years now, this is normal operating conditions for my amp.
Read the manual is my suggestion. I do differ with the 400 MA max for SSB plate current, as I think that is way too high. However, I would not argue with W8JI or encourage others to do anything I do. Just putting it out there for your perusal.

Frank
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W1QJ
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Posts: 2948




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« Reply #38 on: January 31, 2012, 04:59:11 PM »

There is no way an AL-80A can achieve 1100 watts output at a maximum plate current of 400ma with a loaded plate voltage of 2700 volts (not even 3000v).  This is why 500-550 ma full load is talked about to get 1200PEP because that is more realistic.  IMD aside, at that plate current the tube will do that kind of power.  All kinds of ouput numbers get flung around the internet but unless you are using a good 50 ohm dummy load and a good wattmeter most readings into antennas and amplifier wattmeters are bogus.
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K4RVN
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Posts: 261




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« Reply #39 on: January 31, 2012, 05:38:54 PM »

Lou,
The meter readings on the AL80A for SSB would read anywhere from 20 to 50 % of the actual readings on CW. Same on the AL811 or 811H. It is anyone's guess what the true readings are for plate current and grid current on ssb. I read that in the 811 manual about the 20 to 50% of the actual readings so surmised it was the same type meters in the AL 80A.
I could be wrong that's for sure. I figure the man will let me know if I am wrong without hesitation and rightly so. The bottom line is the meters don't read that high on an AL 80A such as 550 MA on SSB.
I have no idea what the real currents are. Anyone who uses the AL 80 A amp showing 550 MA on SSB has a different amp than I do. Just trying to keep these new owners from blowing up something by putting my experience out there on the AL80A. I personally think it is stupid to run a 20 plus year old amp at more than its power tube rating anyway. The IMD must be on the rise not to mention strain on the amp power supply and components for very little or nothing gained.
One could perhaps whistle in the mike on SSB and get a more accurate reading.

It could be 550 Ma  at max out which according to the manual would be around 1200 watts.
If you say so, then it must be so because I don't claim to be an expert and I know of your experience from what I have read. I kinda agree with Dick when he asked how can one tube put out as much power as two 3-500s or something to that effect. I nomally run mine a couple of hundred watts or more below max anyway.


Frank
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W1QJ
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Posts: 2948




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« Reply #40 on: February 01, 2012, 05:04:00 AM »

Frank, for the peak power to effectively reach the value of what 550ma would produce, the amp would need to be properly loaded to that current value.  One can easily load an AL80A or B to 500 to 550 ma with enough drive, as long as the load and tune are adjusted for that drive amount the SSb peaks will indeded be very high.  If one was to load the amp at 400ma (whatever the drive level would be) and then drastically increase drive and push the amp, it won't make the peak SSB power it would had the amp been loaded to that current rating from the start.  Sure a single 3-500 can run close to what a pair run in an SB-220 but not with good IMD. The power will be there.  On the other hand, if one drives an SB-220 with more than 100W they can make 1500 plus out and more.  Of course this is all above ratings etc., but not to say it can't be done.  The SB-220 transformer can produce quite a bit of current in the short term but running like that at length heats it up pretty quick and shorts the windings.  These are the kind of things CBers do Hi
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K4RVN
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Posts: 261




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« Reply #41 on: February 01, 2012, 07:06:41 AM »

I don't disagree with what you said Lou. I also mentioned an external watt meter and a good antenna or dummy load of about 50 ohms impedance in my post. That's another problem with new amp owners who don't own a dummy load and try to use the amp's meters to load a non resonant load for the max power out on their brand new amp or used one.
I am saying to these folks who just acquired an AL 80 A, Don't look for the meters to read 400 to 550 Ma in the SSB operating mode. I load my amp with a watt meter while keeping an eye on the plate and grid in the CW position which will read 550 if you drive it and load it with the correct procedure. The manual in the CW position reads a max of 200MA grid and 550 MA plate in the CW position for around 1200 watts out. The meters will not read that in the SSB mode and from some of the questions I have seen asked on the forum, the newbie owner ops are trying to load the amps in the SSB mode to the max plate MA in the SSB mode which means to me the amp is not tuned if the meter shows that. I really think that's why they are always blowing out the inferior 811a tubes in the 811 and H models also.
These are just my opinions worth less than 2 cents.

Frank
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