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Author Topic: AL-80A/B Do people really get 1kw output?  (Read 7773 times)
WB4JZY
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Posts: 76




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« on: January 02, 2008, 12:36:46 PM »

Is it true this amp can put out over 1kw, as some people say?  How can a single 3-500z produce this much power?
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AD4U
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Posts: 2531




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« Reply #1 on: January 02, 2008, 12:42:04 PM »

I don't think so.  I am not familiar with this particular amp, but I have built my share in my 40+ years as a HAM.  Even if the 3-500 is run at 4000 VDC under load (unlikely in this amp) and at its maximum 400 mA that is 1600 watts INPUT.  It would take around 62.5% efficiency to get 1000 watts out.  I think this just a lot of hype from a company that thrives on hype.
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WA3SKN
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« Reply #2 on: January 02, 2008, 12:48:29 PM »

I think the question is "Should you really get 1kw output?"!!
Linearity and lifespan usually suffer!

-Mike.
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AD4U
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Posts: 2531




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« Reply #3 on: January 02, 2008, 12:55:01 PM »

As a "PS" to my post above - two 3-500 tubes would be pushed about to the limit to give 1500 watts out 160 - 10 meters.  Assuming a 4000 VDC power supply, two new tubes might do this for a while, but they would not last very long.
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N3MVF
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Posts: 21




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« Reply #4 on: January 02, 2008, 12:59:47 PM »

Had one. Hated it. Giot rid of it. Never saw 1kw.  Think it might have smoked if it got that far.  If I recall, I think 750 watts was maxed out at about 60 watts in.  
73
Greg
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W5RKL
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Posts: 1104




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« Reply #5 on: January 02, 2008, 01:00:55 PM »

According to Ameritron's website, the AL-80B amplifier
is designed to produce "UP TO 1KW PEP" output.

http://www.ameritron.com/products.php?prodid=AL-80B

73's
Mike
W5RKL
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SSB
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Posts: 1




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« Reply #6 on: January 02, 2008, 02:43:46 PM »

I talked with application engineering at Eimac back in the 90's when Ameritron was using Eimac tubes.  According to Eimac, if anyone is driving a single 3-500z or zg to 1kw out, then they are exceeding Eimacs absolute ratings for that tube. Period.  Also, Eimac z or zg versions of the 3-500 have exactly the same maximum absolute ratings. Also Period.  Other manufacturers can make up their own ratings.

Alex....
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K0CWO
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Posts: 541




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« Reply #7 on: January 02, 2008, 03:07:30 PM »

All I ever seen on the AL-80A and the AL-80B I used to own, was 800 watts CW measured by a Palstar watt meter.  Could very well be 1KW PEP?  If I had a Bird PEP reading meter perhaps it would show different. The volt and plate meter on the amps support the 800 watts given 60% efficiency.  Driving any amplifier to the last watt which usually means light loading, cause non-linearity and splatter.  The AL-80 A&B are nice amps.  Run them at 600 to 800 watts SSB, they’ll last for ever. On the other guy's S meter it will look like you are running 1000!
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W3LK
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« Reply #8 on: January 02, 2008, 03:12:33 PM »

WB4JZY - Another call sign that's not in the FCC database as of this date.

73,

Lon - W3LK
Naugatuck, Connecticut
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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
W8JI
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« Reply #9 on: January 02, 2008, 03:14:46 PM »

Some people are giving authoritative answers, but they obviously don't understand tube operation or heat or other issues related to power grid tubes.


What they have most likely done is grabbed something from a typical operation chart and assumed there is only one set of operating conditions for tube operation.


The 1000 w PEP out is the IVS (Intermittent voice service) operation rating of the tube. The amp is rated at about 800 watts out on CW carrier, and the manual says to not go over 400mA on CW carrier. That's because on CW the average plate current can be as high as 400mA for rated heat limits. The anode dissipation (heat) is based on Pin - Pout (Pout has to be adjusted to not include any external losses like tank losses, since they do not heat the tube). So at about 400mA and about 800W output the anode dissipation will be 400 watts or less.

At a short term average anode current (which is what the meter shows) of 400mA, the peak cathode current will be 1.6amps. All of which is perfectly safe for the 3-500Z.

On voice the average anode current will be about 200-300mA at 1000W PEP output, and average output would be 200-500 watts depending on processing and audio waveshape. The instantaneous peak emission current would be about 1.9 amps, which is still well within peak emission limits. So the dissipation would be 300 watts or less typically on voice. Perfectly safe.

The tube won't have shorter life or any other noticeable problem when operated at 1000W or even more PEP on voice, and IMD is quite acceptable at 1000W PEP. It measured about -33dB one tone of two equal tones, which is -39dB PEP. Most radios are only around -30 or -35 below PEP, so the amp won't substantially change the IM performance at 1kW PEP when properly tuned.

As a matter of fact as long as we don't overheat the elements in a thoriated tungsten tube to the point of physical damage there is no life shortening at all due to excessive emission current. So what people are pulling out of their rear pockets is simply not accurate. They are probably just inventing it without actual experience or science.

By the way, this is NOT true for metal oxide cathodes. A metal oxide cathode can be stripped from excessive HV or excessive cathode current (or low cathode temperature operation), but a thoriated tungsten emitter like the 3-500Z is immune to that. A tube like the 3-500Z wears out from net filament hours at a certain filament voltage, not emission hours at a certain cathode emission. It also is not damaged by the AMOUNT of emission demand, unlike the oxide cathode that is quickly destroyed by excessive emission demand.


As a matter of fact Eimac in Salt Lake was aware of and approved the IVS operation of that amp. They always gave full warranty on tubes when operated as rated in the manual. Amperex did the same, also based on IVS service for voice and ICAS for CW.


The FCC approved the amps under that rating, Eimac had no problems, and Amperex also looked at and approved the operation. IMD was tested at that level, and anyone who knows anything at all about thoriated tungsten tubes or even general tube operation would understand the difference between CCS carrier (at 400mA) and PEP voice operation.


73 Tom


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W8JI
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« Reply #10 on: January 02, 2008, 03:40:07 PM »

By the way, for the "experts" here who oddly think a two tone test continuous commercial service rating applies to IVS operation...

Here is a quote from Care and Feeding of Power Grid tubes:

"The power-handling capability of a given tube in single-sideband service depends upon the nature of the signal being transmitted and the power dissipating capability."

This is why IVS is always higher than a steady level two-tone PEP rating.

Also:

"It is impractical to establish a rating based on voice signal modulation because of the irregular waveforms encountered and the varying rations of peak to avarage signal power found in various voices."

This is why the typical operation ratings are based on a steady uninterrupted two tone test, and why IVS operation can easily exceed those levels for PEP voice without harm.

I'm suprised to see people who actually think the life of a thoriated tungsten cathode tube is somehow tied to emission current! It's a long term dissipation and IMD issue, not peak envelope limitations.

73 Tom
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WB2WIK
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Posts: 21830




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« Reply #11 on: January 02, 2008, 04:13:00 PM »

I have an AL-80B.

With ~70W PEP drive, it produces ~1kW PEP output power measured on everything I have, including a Bird 43P/1000H, my Autek WM-1 PEP meter, and its own internal PEP cross-needle meter: All of these read within a few percent of each other.

It will run a bit over 1kW PEP on CW with a fast string of dits.

I usually only drive it with about 55W, so it normally doesn't make 1kW, but the Ig never exceeds 100mA this way and it makes me feel good.  It'll still make about 700W PEP.

Line voltage regulation may play a small role in this; I have a very stiff 240V line coming to the amp and B+ only drops from 3kV to about 2700V key-up to key-down.  I've seen others vary more than this, especially when powered by a long 120V circuit.

I have the original Amperex tube, placed into service December 2000, so it's been a few weeks over seven years.  It's used almost every day.

WB2WIK/6

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SSB
Member

Posts: 1




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« Reply #12 on: January 02, 2008, 06:11:02 PM »

Toward the end of glass tube production at Eimac, and according to Eimac, they told Ameritron that they would not warranty any more 3-500Z tubes from the Al80A amp.  That's when Ameritron switched tube manufacturer.  Eimac was disassembling warranty return 3-500's and found they were failing because their ratings were being exceeded.

Alex....
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W8JI
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« Reply #13 on: January 02, 2008, 06:49:50 PM »

Alex,

You shouldn't say or invent things that you don't know as a fact or were not involved in first hand.

Eimac **never** told Ameritron that.

The very last batch of 3-500Z's from Varian Salt Lake, just prior to closing, was 100% defective out of the box. Ameritron received about 100 tubes in that last batch that was manufactured by employees who were about to lose their jobs. It was part of closing out a 500 tube purchase order.

The nature of the failure was the tubes would arc at voltages over a few thousand volts. They either were not pumped down properly through an error, or they were intentionally sent out defective by someone about to lose his  or her job.

Varian sold the 3-500Z's along with the warranty obligations to a company called Triton in PA that made some other industrial glass tubes. After waiting for one or two years for replacements for the defective lot of 3-500Z's that was Salt Lake's last run, and several failed attempts by Triton to make good tubes, Ameritron received a refund from Triton on all the returned tubes.

What Eimac actually told Ameriton (and everyone else) was that Triton purchased the tubes and all warranty obligations, and so Eimac Salt Lake had no responsibility for manufacturing defects in the warranty period beyond the sale of the glass tube line.

73 Tom

 

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SSB
Member

Posts: 1




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« Reply #14 on: January 02, 2008, 07:05:46 PM »

Well, I sure don't know first hand what was going on at Eimac, but Brandon Reed (or is it Reed Brandon) knew what was going on.  He worked there for over 20 years and much of my 'bad information' came from him or Joe Emsley.


Alex....
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