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Author Topic: Silly question ?  (Read 1589 times)
KB2HUK
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Posts: 164




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« on: November 02, 2012, 07:34:44 PM »

Is it possible to drive a Alpha 87a amp with a 5 watt qrp radio ?  has anyone ever done it ?  Is it good for the amp?  thanks  John kb2huk
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KE6EE
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Posts: 410




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« Reply #1 on: November 02, 2012, 08:01:34 PM »

www.hamradio.com/documents/87amanual.pdf

Where it sez 50 to 55 watts required for full output.
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KB2HUK
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« Reply #2 on: November 02, 2012, 08:18:39 PM »

I am only looking for around 2 to 300 watts out .  John
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K1ZJH
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Posts: 1099




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« Reply #3 on: November 02, 2012, 08:52:44 PM »

It won't hurt the amp, or the 8877 PA tube.  But, because of the quiescent idling current, it won't be extremely efficient. It should work but of course the amp will running no where near full power.

Pete


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K2DC
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« Reply #4 on: November 03, 2012, 04:08:24 AM »

The 87A is not an 8877 tube, it's a pair of 3CX800's.  It shouldn't hurt the amp at all, although it certainly won't operate as efficiently as it would at full output.  With 5W of drive, I would expect 130-150W output, depending on the age and condition of the tubes.

73,

Don, K2DC

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K1ZJH
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« Reply #5 on: November 03, 2012, 06:43:09 AM »

The 87A is not an 8877 tube, it's a pair of 3CX800's.  It shouldn't hurt the amp at all, although it certainly won't operate as efficiently as it would at full output.  With 5W of drive, I would expect 130-150W output, depending on the age and condition of the tubes.

73,

Don, K2DC



I stand corrected. I'd be worried if it used tubes like 3-500s or similar that needed plate color to properly getter.

Pete
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KE6EE
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« Reply #6 on: November 03, 2012, 04:58:05 PM »

I am only looking for around 2 to 300 watts out .  John

I thought the whole thing about the 87a was its totally-automated operation--for which it requires a minimum of 20-25 watts of drive.

Doesn't sound like it's an appropriate match for your QRP radio. I understand they're not particularly inexpensive.
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K0CWO
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Posts: 419




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« Reply #7 on: November 03, 2012, 05:59:21 PM »

FWIW, I've owned seven Ameritron amps over the last 10 years. (AL-811, AL-80A, AL-80B, AL-1200, AL-1500, ALS-600, ALS-1300)  I still own three.  With the exception of the ALS-1300 I'm fond of all of them.  I have a 22 year old AL-80A (probably not Mississippi made?) with original tube that works flawless.  I also have a five year old AL-1500 that I believe is good bang for the buck.  I have had other amplifiers.  I do not want to bash any brand but some of those have had occasional issues.  No more no less than most reputable amateur amplifiers on the market that I now and hear of.  If I was in the market for a new amp I think I would try an AL-82.  I've owned an AL-80B.  If I was in the market for a 1KW amp I would buy another AL-80B in a heartbeat.  For a person who does not want go through the trouble of getting 240 into the shack this little amp works great with a stiff 120 supply.

You guys have fun!

BJ
k0cwo


 
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K0CWO
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« Reply #8 on: November 03, 2012, 05:59:56 PM »

Sorry, wrong post.............
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