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Author Topic: Flex 1500 driving AL-80A  (Read 5670 times)
K8CIT
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Posts: 31




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« on: February 03, 2012, 05:00:09 AM »

Hello all.  I'd like the amplifier experts opinion on this situation:  I am driving my AL-80A amp with my new Flex 1500.  Here are the parameters: Ip = 140 ma, Ig = 25 ma, Ep = 2950 v, Po = 110 w as read on a Bird wattmeter.  This is for keydown CW.  See any problems?  Thanks in advance.  73, Art K8CIT
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W1QJ
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« Reply #1 on: February 03, 2012, 05:07:00 AM »

The problem is you do not have enough drive from that radio to use the amp in its effective power band.  Running the amp too low in the power band does not make the best use of it and you have little advantage over a simple 100w radio.  It's kind of a waste.
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W8JX
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« Reply #2 on: February 03, 2012, 05:12:13 AM »

The problem is you do not have enough drive from that radio to use the amp in its effective power band.  Running the amp too low in the power band does not make the best use of it and you have little advantage over a simple 100w radio.  It's kind of a waste.

I agree. Poster would really be better with a AL500 or 811 amp here as it should also show more gain with good tubes. Also, the tube in AL80 is being under utilized and will very likely not even get warm enough to properly stay gettered.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
K8CIT
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« Reply #3 on: February 03, 2012, 05:55:26 AM »

Thank you for the replys.  The point of using the AL-80A with the Flex 1500 was to get it up to the 100 watt level.  I really wasn't expecting much more than 100 watts from the amp in this service.  I also use the amp with my IC756p3, so the tube gets warm from time to time.
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W8JX
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« Reply #4 on: February 03, 2012, 06:02:41 AM »

I understand but you "could" buy a new or used AL500 and use it as a driver for AL80 when using Flex 1500 at proper output level to drive it all properly and then use AL 80 amp the way it was meant to be used. 
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Ham since 1969....  Old School 20wpm REAL Extra Class..
KE5JPP
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« Reply #5 on: February 03, 2012, 06:07:32 AM »

Supposedly the Flex 1500 has pretty bad IMD, so watch yourself for splattering when driving the AL 80A.  Running the AL 80A at that low of power output also may exacerbate the IMD problem too.  To get maximum smoke out of your AL 80A you are probably running the 1500 at max output.  This will make the splatter problem even worse.

Gene
« Last Edit: February 03, 2012, 06:09:04 AM by KE5JPP » Logged
K2DC
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« Reply #6 on: February 03, 2012, 08:42:16 AM »

You're also wasting some prime power there.  The efficiency is just under 27%, so you're wasting just over 300W.  That's about as much heat as you would be generating if the amp was properly driven for an output of about 750W.

73,

Don, K2DC

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K8CIT
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« Reply #7 on: February 03, 2012, 10:04:21 AM »

Guys...I understand that there are some inefficiencies here.  For a few minutes operation per day I'm not going to worry about them.  The Flex 1500 has no worse IMD than any other rig, so I don't believe that's a concern, either.  The point of my question was to determine if there would be any detrimental effects to the amp running it as I described.  On those days I don't feel like being QRP, if all I get is 100 watts or so, I'm happy.   
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WB2WIK
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« Reply #8 on: February 03, 2012, 10:34:53 AM »

At such low power I cannot imagine any detrimental effects to the amplifier.

At greatly reduced drive I'll be the LOADing control is a lot more counterclockwise (meshed) than it would be at normal drive levels, but the power is so low I doubt that will cause any problems.

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K8CIT
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« Reply #9 on: February 03, 2012, 12:39:02 PM »

Thank you for the direct answer to my question.
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NO2A
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« Reply #10 on: February 03, 2012, 04:28:54 PM »

I`ve heard Tom say that driving that amp too low isn`t good on the tube anode. Maybe someone can comment on this.
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WB2WIK
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« Reply #11 on: February 03, 2012, 06:34:25 PM »

I`ve heard Tom say that driving that amp too low isn`t good on the tube anode. Maybe someone can comment on this.

I don't recall reading that.  Efficiency suffers and the tube gets warmer than one might think, but it shouldn't be destructive in any way because anode dissipation is still well within ratings.

All amplifiers work at maximum effiency when they're operating at maximum power and fully loaded.  An amp driven lightly is very underloaded, but it shouldn't hurt anything.

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