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Author Topic: AL80B, grid and plate current  (Read 8410 times)
W7HBP
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Posts: 164




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« on: April 15, 2013, 07:51:48 AM »

Ok, when you AL80B users tune these up for optimum, what readings are you getting on the grid and plate.
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NO2A
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Posts: 768




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« Reply #1 on: April 15, 2013, 09:27:32 AM »

I have an AL-80A,which is similar to yours. Depending on your ac mains voltage,(I run mine on 120v) I get rated or near that with 100ma grid,and plate can be anywhere from 400-500ma. I have a voltage drop at my shack cause of a long run. Ideally,with proper voltage the plate current might not go over 400ma. You will,with proper voltage get more than the rated 850 watts out,but I wouldn`t do that. Some say it`s ok to run as much as 150ma grid. I stick to 100,like the manual says. Grid current is the most important thing to worry about,plate current is whatever it is. Values can vary somewhat from band to band also. Your amp might "like" 80m better than 10m.
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WB2WIK
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« Reply #2 on: April 15, 2013, 10:39:59 AM »

When all is optimized, with my AL-80B Ip is 150mA maximum and anywhere from 450 to 600mA Ip, depending on the band and the load.

I use the ALC connection to limit Ig to 150mA, so even operator errors won't let it exceed that.

Ip can run 600mA and even above that for short duty-cycle modes like SSB and CW.  Don't try it on digital modes or FM.  For AM work, I limit carrier power to 150W (600W PEP output) and average plate current is pretty low, around 200mA but peak Ip can run easily 400-500mA.
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W8JX
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« Reply #3 on: April 15, 2013, 11:52:57 AM »

The tube is "rated" for 400ma max and higher currents can shorten its life. The way to "safely" get more power out of a single tube is to raise its plate voltage not its plate current for what its worth.
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W1QJ
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Posts: 1444




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« Reply #4 on: April 16, 2013, 03:27:25 AM »

The tube is "rated" for 400ma max and higher currents can shorten its life. The way to "safely" get more power out of a single tube is to raise its plate voltage not its plate current for what its worth.

True. but that rating is key down 24/7.  For the tube to make the rated 1000w pep ssb output the anode current would probably peak 550ma.  If you look at the tube anode during an extended 1000w pep ssb transmission it would not show any more over all anode color than it would if you keyed down constantly at 400ma for a small period of time.   For the most part what ruins a tube is over dissipation not so much as the peak anode or grid currents.  There is a time factor in over dissipation damage to a tube and it generally is not reachable in an overall ssb casual transmission.  It does take place with high compression (speech processing) for extended time.  Like using processing and voice keyers in contest mode.  This is why time restrictions and PO limits are put on rtty use.  A 3-500 tube will easily handle the ssb pep kw peak limit for the casual un processed signal.  This is our ICAS rating
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W8JX
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« Reply #5 on: April 16, 2013, 06:04:14 AM »

The tube is "rated" for 400ma max and higher currents can shorten its life. The way to "safely" get more power out of a single tube is to raise its plate voltage not its plate current for what its worth.

True. but that rating is key down 24/7.  For the tube to make the rated 1000w pep ssb output the anode current would probably peak 550ma.  If you look at the tube anode during an extended 1000w pep ssb transmission it would not show any more over all anode color than it would if you keyed down constantly at 400ma for a small period of time.   For the most part what ruins a tube is over dissipation not so much as the peak anode or grid currents.  There is a time factor in over dissipation damage to a tube and it generally is not reachable in an overall ssb casual transmission.  It does take place with high compression (speech processing) for extended time.  Like using processing and voice keyers in contest mode.  This is why time restrictions and PO limits are put on rtty use.  A 3-500 tube will easily handle the ssb pep kw peak limit for the casual un processed signal.  This is our ICAS rating

The cathode is not immune either to higher current rates and higher rate can cause the tube to "soften" sooner due to reduced  emissivity of cathode
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AD4U
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« Reply #6 on: April 16, 2013, 06:07:01 AM »

I probably should keep my mouth shut or my fingers off the keyboard.  We beat this subject (and each other) to death several months ago.  I am not suggesting that an AL-80B amp will not put out 1000 watts PEP on some bands.  It will.

I have the EIMAC data sheet for their 3-500Z tube in front of me.  Assuming the tube is properly cooled per EIMAC's specs (not so in the AL-80 series of amps) the issue here has absolutely nothing to do with exceeding the tube's plate dissipation rating of 500 watts CCS.  IMO the issue is exceeding EIMAC's published maximum (do not exceed under any circumstances) plate current rating of 400 mA per tube.  

NO WHERE in the EIMAC data sheet on their 3-500Z tube is it stated that it is OK to run the tube at 500-600 mA in SSB service.  Doing so will (may) operate the tube out of its linear region.  This will (may) result in a "dirty" signal.  After all linear amps are called LINEAR amps for a reason.

As previously posted the best way to make the  AL-80 series of  amps put out 1000 watts and operate within EIMAC's published specs is to up the plate voltate to 4000V as recommended in the EIMAC data sheet.  Then if the tube is operated at the maximum 400 mA as published in the EIMAC data sheet, the PEP input will be 1600 watts and the PEP output will be an honest and clean 1000 watts.

Dick  AD4U
« Last Edit: April 16, 2013, 06:26:10 AM by AD4U » Logged
W1QJ
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Posts: 1444




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« Reply #7 on: April 16, 2013, 07:27:03 AM »

Guys, I am only giving an explanation on how the AL-80B is rated to do 1000w pep according the the Manufactuer.  Tom Rausch designed and rated this amplfier as he did.  If you look on the internet somewhere, you will find his explanation on how he went about rating the amp as he did.  He does cover in some detail his thought about tube parameters and what actually causes tube damage.  He cliams there are some common misconceptions about this.  And of course no tube company or any company that makes a product would wnat you to deleve into an area where they would have to make good on warranties if they told you to run a tube any way you wanted.  So 400ma is there stated limit and once again, that is a 24/7 rating.
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W8JX
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« Reply #8 on: April 16, 2013, 08:01:24 AM »

In all fairness if you wanted to make a reliable linear 1kw amp using a single 3-500 you would use more than 27 to 2800 volts under load.  More like 35 to 3700 v under load.
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WB2WIK
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« Reply #9 on: April 16, 2013, 09:06:15 AM »

 IMO the issue is exceeding EIMAC's published maximum (do not exceed under any circumstances) plate current rating of 400 mA per tube.  

NO WHERE in the EIMAC data sheet on their 3-500Z tube is it stated that it is OK to run the tube at 500-600 mA in SSB service.  Doing so will (may) operate the tube out of its linear region.  This will (may) result in a "dirty" signal.  After all linear amps are called LINEAR amps for a reason.



Eimac hasn't built a 3-500Z in decades.  The tubes used in the AL-80B aren't Eimacs, they're 3-500ZGs (graphite anode) built elsewhere.

Philips (now Richardson) specs the Amperex 3-500ZG quite differently.  If you refer to the Amperex data sheet, (lower section of page 3) they list OPERATING CONDITIONS as 3000Vdc Ep, and 770mA peak anode current, for 1420W peak output power (single tube): http://www.mhzelectronics.com/ebay/manuals/amperex_3-500z_tube_datasheet.pdf

I have no idea why people still refer to Eimac data sheets that are 40 years old, when Eimac doesn't manufacture this tube. Wink
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AD4U
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Posts: 2156




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« Reply #10 on: April 16, 2013, 10:07:31 AM »

"Eimac hasn't built a 3-500Z in decades.  The tubes used in the AL-80B aren't Eimacs, they're 3-500ZGs (graphite anode) built elsewhere.

Philips (now Richardson) specs the Amperex 3-500ZG quite differently.  If you refer to the Amperex data sheet, (lower section of page 3) they list OPERATING CONDITIONS as 3000Vdc Ep, and 770mA peak anode current, for 1420W peak output power (single tube): http://www.mhzelectronics.com/ebay/manuals/amperex_3-500z_tube_datasheet.pdf

I have no idea why people still refer to Eimac data sheets that are 40 years old, when Eimac doesn't manufacture this tube. Wink "


On page 3 of the Amprex 3-500ZG tube data sheets that you linked us to, the maximum peak plate current of 770 mA is for a single tube in an AUDIO AMPLIFIER or a MODULATOR.  

If you refer to page 2 of the Amprex 3-500ZG tube data sheet and look under LINEAR AMPLIFIER service, the ABSOLUTE MAXIMUM plate current of the Amprex 3-500ZG tube in LINEAR AMPLIFIER service is 350 mA.

Dick  AD4U

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W8JX
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Posts: 5591




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« Reply #11 on: April 16, 2013, 02:21:08 PM »

What we need is for them to bring back/make 3-1000z's in China then you can have a real solid 1kw plus single glass tube amp.
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K0CWO
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Posts: 418




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« Reply #12 on: April 17, 2013, 11:43:45 AM »

Resurrecting a 3-1000 tube would be cool!  On the other hand my 23 year old AL-80A with the 23 year old Emacs 3-500 are still going strong @ 1KW SSB PEP (frequent ragchew) output today.
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K4RVN
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Posts: 760




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« Reply #13 on: April 17, 2013, 11:54:15 AM »

The tube is "rated" for 400ma max and higher currents can shorten its life. The way to "safely" get more power out of a single tube is to raise its plate voltage not its plate current for what its worth.

True. but that rating is key down 24/7.  For the tube to make the rated 1000w pep ssb output the anode current would probably peak 550ma.  If you look at the tube anode during an extended 1000w pep ssb transmission it would not show any more over all anode color than it would if you keyed down constantly at 400ma for a small period of time.   For the most part what ruins a tube is over dissipation not so much as the peak anode or grid currents.  There is a time factor in over dissipation damage to a tube and it generally is not reachable in an overall ssb casual transmission.  It does take place with high compression (speech processing) for extended time.  Like using processing and voice keyers in contest mode.  This is why time restrictions and PO limits are put on rtty use.  A 3-500 tube will easily handle the ssb pep kw peak limit for the casual un processed signal.  This is our ICAS rating
In support of W1QJ, I have read SSB does not require a solid, uninterrupted rf carrier for any prolonged period of time. There is an average that takes place - half above the tubes maximum rating and half below. Consequently, we can load the tube to deliver twice the amount of current at signal peaks, understanding that the lulls will fall far below the tubes dissipation ratings. In this way, the tube will the average amount of power the tube will be called upon to dissipate will not exceed its ratings. Bottom line is one can run a single 3-500 tube at 1000 watts as many have done for years with around 3000 volts. Just another view for your perusal





« Last Edit: April 17, 2013, 12:01:26 PM by K4RVN » Logged
W1QJ
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Posts: 1444




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« Reply #14 on: April 18, 2013, 04:09:22 AM »

RVN is totally correct, energy dissipation is energy dissipation.  For example, My nephew is 26 years old and in perfect health.  He can unload a truck full of 40lb fuel pellets (100 bags 2 tons) in about 20 minutes and stack neatly for me in my garage.  I am going to be 61 in May and if I try to keep up the pace he does with unloading I will have a heart attack.  I could complete the job in maybe an hour but I CAN DO IT.  I'll stop for awhile or work slower, but I can get the job done. We will both dissipate the same amount of energy to complete the task.  He dissipated his energy in a shorter time and works constantly like a steady carrier on a tube.  I will take me 3 times the amount of time as him to dissipate the same energy like a tube working under SSB conditions, which is about 33% less than full carrier.  Maybe a poor analogy but I think you can see the difference in the dissipation over time which is the limiting factor with the tube.  Did you know that a 3-500 can produce about maybe 5KW of pulse energy?  Look at the pulse rating on "P" rated tubes in pulse operation.  There, the pulses are so quick the duty cycle is way less overall and the dissipation vs power putput is almost unbelievable.
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