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Author Topic: AL 80A How to tune an amp.  (Read 23977 times)
K4RVN
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Posts: 261




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« Reply #15 on: January 20, 2012, 07:34:51 PM »

Mike,
The Eimac tube specs indicate a max of 400 MA plate while the voltage can be as high as 4000. The plate current spec. max remains 400 even with lower HV so I suppose the manual writer wanted to stay within tube parameters for the 3-500. I really don't know but it has been no problem for me. My average plate current on 1000 watts out pep runs less than 400 about 150 or so but hard to pin down on voice peaks with a great deal of accuracy. My grid current usually peaks about 50 as best as I can see under SSB operation. How does this compare with your AL80A? BTW, how is your amp operating now? I have not read anything since the posting you made on the HV drop/ maybe a line voltage drop problem.

http://home.c2i.net/clank/ham/pa/3-500z.html#rfcd4

Frank
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K0CWO
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« Reply #16 on: January 20, 2012, 08:36:38 PM »

Feeding my AL-80A 120 volts results in 3150 idling PV (400 volt drop 800 watts RTTY), drive @ 70 watts SSB produces 1000 watts PEP output as read by the meter in an ATR-30 tuner with about 150 mils plate current and 40 mils grid current on 75/80.  The Eimac 3-500Z is about 20 years old. 
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K4RVN
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« Reply #17 on: January 20, 2012, 09:41:46 PM »

Thanks for info, looks like we have similar conditions. I use about 55 to 60 watts drive most of the time for 800 to 900 out. I love this amp. Mine is on 240 volts line.

Frank
« Last Edit: January 20, 2012, 10:21:14 PM by K4RVN » Logged
K0CWO
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« Reply #18 on: January 21, 2012, 04:17:18 AM »

You are welcome Frank.  Hope all is well with you and yours.

BJ
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NO2A
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« Reply #19 on: January 23, 2012, 07:05:38 PM »

Hi Frank! I`ve been running my rig off a different circuit than the amp. It has made a difference,with a smaller voltage drop in my amp,but it still needs rewiring. I have been using it as is until I can get an electrician to upgrade it.-Mike.
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W8JX
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« Reply #20 on: January 23, 2012, 07:28:10 PM »

They higher the plate voltage the more output you will get at any given drive level.
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--------------------------------------
Ham since 1969....  Old School 20wpm REAL Extra Class..
W8JI
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« Reply #21 on: January 24, 2012, 05:24:04 AM »

Another manuel problem is the plate current max of 400ma. Provided the amp is tuned properly,you will never get max power out with only 400ma. More likely it would be 450-550ma. The point is this is misleading to new owners of this amp. The most important thing is grid current,and enough hv.

The manual actually allows tuning at full power an 550 mA for handling peaks on SSB, which was approved by Eimac, but for CW instructs reducing drive to 400 mA plate current.  This is primarily for heat in the transformer and tube on higher average power modes like CW.

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AD4U
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« Reply #22 on: January 24, 2012, 06:33:28 AM »

Being an old timer, who has built his share of HAM amps, I still have copies of some of Bill Orr's books (W6SAI).  Bill Orr was one of the engineering guru's at EIMAC, the company that "invented" the 3-500Z tube.  The title of one of Bill Orr's books is, "The Care And Feeding Of Power Grid Tubes".

According to this book and quoting from the EIMAC data sheet (available on the internet) the EIMAC 3-500Z tube has a  maximum plate current of 400mA.  I don't think this limit was to prevent exceeding the recommended power dissipation of the tube (especially in SSB and CW service), but it was to make sure the tube was not driven out of its "linear" region.  

It is definitely possible to continue to increase drive to a 3-500Z (or most any other transmit tube for that matter) until the plate current (cathode current for the purists) exceeds the tube's rated value.  Every transmitting tube has accompanying operating "curves" that show what the tube will do in different class amps, with different plate voltages, screen voltages, grid voltages, drive, etc. 

I always thought that in order to have a true LINEAR AMPLIFIER, tubes should be operated within the LINEAR portion of the published operating curves.  I also thought that if any tube used in a linear amp was driven out of its linear region (hence the name LINEAR AMPLIFIER) it could result in a "dirty" signal and "splatter".  I COULD BE BADLY WRONG.

Within the past 15 minutes I re-read the EIMAC data sheet on their 3-500Z tube, and no where can I find any reference or recommendation that the EIMAC 3-500Z can be driven to a plate current of 500 - 550 mA, even in SSB service.

I am sure my post will be like kicking a fire ant's mound, but 400 mA is the maximum published plate current (in any mode and for any application) that I was able to find on any of the EIMAC data sheets for their 3-500Z tube.

Go Ahead.  Shoot back!

Dick  AD4U
« Last Edit: January 24, 2012, 10:45:20 AM by AD4U » Logged
W8JI
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« Reply #23 on: January 24, 2012, 05:07:02 PM »

Being an old timer, who has built his share of HAM amps, I still have copies of some of Bill Orr's books (W6SAI).  Bill Orr was one of the engineering guru's at EIMAC, the company that "invented" the 3-500Z tube.  The title of one of Bill Orr's books is, "The Care And Feeding Of Power Grid Tubes".

Bill was in marketing and customer service, not engineering. He was in San Carlos, not Salt Lake. He didn't write Care and Feeding. It started as a collection of questions and answers by staff. Bill did compile and edit the Radio Handbook, which we all grew up with as an alternative to the ARRL Handbook.

Quote
According to this book and quoting from the EIMAC data sheet (available on the internet) the EIMAC 3-500Z tube has a  maximum plate current of 400mA.  I don't think this limit was to prevent exceeding the recommended power dissipation of the tube (especially in SSB and CW service), but it was to make sure the tube was not driven out of its "linear" region. 


Well, I know how they determine grid dissipation and other things, but I'm not sure how they determined the maximum average plate current. It was a carrier condition rating. That implies IMD was not involved.

I'm not sure what you are proposing. That a 3-500Z can last 5,000 hours at 400mA, but if it reaches 500-550 mA for a few seconds it will fail? Why would that happen? What does carrier tune stopping point have to do with SSB? Does the meter say 400 on SSB?

Quote
I always thought that in order to have a true LINEAR AMPLIFIER, tubes should be operated within the LINEAR portion of the published operating curves.  I also thought that if any tube used in a linear amp was driven out of its linear region (hence the name LINEAR AMPLIFIER) it could result in a "dirty" signal and "splatter".  I COULD BE BADLY WRONG.

Odd order IM depends on the slope of the transfer function, so a proper curve will be non-linear without harmful IM.

The best way to know what the safe rating is would be to measure IM in the actual amplifier. Many things affect that, including cathode system impedance and feedback.

Quote
Within the past 15 minutes I re-read the EIMAC data sheet on their 3-500Z tube, and no where can I find any reference or recommendation that the EIMAC 3-500Z can be driven to a plate current of 500 - 550 mA, even in SSB service.

Eimac engineering said it was perfectly fine, it doesn't affect life, and IMD is acceptable,  so that was good enough for me. It's well-known IVS ratings are acceptable if verified.

It's been about 20-30 years now. One would think there would have been a problem show up.  :-)

73 Tom
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K4RVN
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« Reply #24 on: January 24, 2012, 07:33:19 PM »

 Dick, did you ever see these links?

http://hamgallery.com/Tribute/W6SAI/w6sai.pdf

http://www.semara.org/files/zerobeat/2001-03.pdf

Frank

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AD4U
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Posts: 2538




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« Reply #25 on: January 25, 2012, 06:52:42 AM »

Thanks Frank K4RVN.  Yes I have seen the two links you provided.  Apparently somebody (perhaps I) is (are) confused as to what Bill Orr W6SAI actually did at EIMAC.  All I can do is read the published information on him and reach conclusions based on what I read.  I did not work for EIMAC and I did not know Bill Orr personally.

Thanks Tom W8JI.  I will never try to take issue with anything you post.  Your knowledge on most subjects obviously greatly exceeds mine.  

Many years ago I bought the brown, hard cover, copy of Bill Orr's Handbook, which I still have and use.  At the same time I also bought copies of paper bound books that I think he wrote - Beam Antenna Handbook - Quad Antenna Handbook - Wire Antenna Handbook.  In the same package I also bought a book called "The Care And Feeding Of Power Grid Tubes".  

I still have all of them but I did not go and root out these books to make sure that Bill Orr wrote each of them.  I am almost 100% sure that he wrote the three antenna books I referenced above.  I apologize to the real author if I gave Bill Orr credit for writing, "The Care And Feeding Of Power Grid Tubes".

I was not inferring anything except that I can find NO published data where EIMAC said that plate current on their 3-500Z should (could) exceed 400mA in any service.  I looked on the internet and I still have an original yellow and white copy of the EIMAC data sheet on their 3-500Z.  I would be interested in a link to some published EIMAC data that states otherwise.  

That is why I have always thought that AL80 amps were a bit optimistic when they claimed 1000 watts output based on a single 3-500Z tube running at a nominal 3000 VDC or a bit less (under load) and 400 mA plate current, the maximum as published by EIMAC.  If the 3-500Z in the AL80 were running with 4000 VDC on the plate and 400mA plate current, then 1000 watts output would be more realistic and in keeping with EIMAC's published data..

I never meant to infer that running a 3-500Z at more than 400mA plate current would immediately destroy the tube or even shorten its life.  I did state that running the tube like this exceeded all EIMAC published data that I can find.  I also questioned whether or not running a 3-500Z at 550mA plate current would cause the tube to operate out of its linear parameters.

After all I have owned and used a Drake L4B amp for over 40 years.  My L4B still runs the same two EIMAC 3-500Z tubes that came in the amp.  They provided 1200 watts output in 1972 and they still provide 1200 watts output in 2012.  This output comes at 2800 VDC and 800mA plate current for the two tubes.

Dick  AD4U

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K4RVN
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Posts: 261




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« Reply #26 on: January 25, 2012, 07:16:18 AM »

You are welcome Dick. My AL80 A will put out on SSB more than 1100 watts on the watt meter. I think the old manual cautions about exceeding 1200 watts, but not sure about that since I have not read it in a long time. Tom did a great job on the AL 80A as mine is on its 23rd year and doing well. I heard W8JI designed the amp. It's simple and does the job.
Anyway the manual is not kidding when it reads 1000 watts with a 3-500. I actually exchanged emails with Bill Orr before he passed away. I shipped Bill my old Eico 50 watt Hi FI amplifier to California that he was looking for. In exchange he sent me an autographed All about Cubical Quads latest edition with a personal hand written note to me. I use my old book and keep the one from Bill in my desk.

Frank
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AD4U
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« Reply #27 on: January 25, 2012, 08:52:23 AM »

Thanks for the reply, Frank.  I realize this post has wandered way off from the original post.

I do not own an AL80, but I have worked on a few.  I have one in the shop right now.  I often think the problems some HAMs have with the AL80 amp (and other amps) are due to operator error, not a problem with the amp itself.  In fact I am seriously looking at buying one.

I am not disputing the output power that you get from your AL80 amp.  However I still cannot understand how (why) an AL80 amp running a single 3-500Z tube will put out just as much power as my Drake L4B that runs two 3-500Z tubes.  My L4B runs ALMOST as much high voltage as the AL80 (2800 vs 3000) and TWICE the plate current (800mA vs 400mA), but only puts out 100 watts more power?!?!?!

Maybe I need to drive my L4B with 200 watts instead of the specified 100 watts.  Then I could run 1100mA plate current and get 2400 watts out - HI! 

On the other hand several times I have considered building a home brew PS for my L4B that would put around 4000 volts on the plates of the two 3-500Z tubes under load.  That, along with a few mods to the L4B to reduce idling current etc, would IMO really make the L4B "sing".

I really don't think the AL80 is any more efficient than the L4B.  Since I am very familiar with both amps, IMO the L4B tank circuit LOOKS to be much more robust and RF efficient (heavier looking components) than the AL80 tank circuit.

The discussion continues.

Dick  AD4U





With 
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W1QJ
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« Reply #28 on: January 25, 2012, 09:29:49 AM »

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.
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NB8I
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« Reply #29 on: January 25, 2012, 11:16:34 AM »

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

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