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Author Topic: New Amp isn't working now :(  (Read 541 times)
KT4FD
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Posts: 4




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« on: February 24, 2002, 09:18:49 PM »

Well, 24 hours after setting up my new AL-572, and testing on all bands, I've hit my 1st problem.

While tuning on 75, The swr was getting a little high, probably around 2:1 with about 45-55 watts drive to the 572.  Suddenly, a few things popped ( sounded like it was near the tube area, but I'm not sure as I had the cover on of course ) and then the amp lost power.

After checking the fuse box, and verifying that the fuse wasn't thrown, I unplugged the amp and opened it up.  LOTS of heat coming from in there.  I allowed to to cool, then I looked at what I could, but didn't notice anything.  Nothing smoldering, and no signs of anything burnt.

I can't tell if the fuses are blown as the 20 amp fuses are covered with a black coating.

Any ideas on this ?  What should I do oter than try replacing the fuses 1st ?

Please email me at:   shep1478@starband.net


Thanks in advance!
Jim
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WB2WIK
Member

Posts: 20612




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« Reply #1 on: February 25, 2002, 06:50:30 PM »

Well, Jim, it sounds like the fuses are blown -- the black coating inside is likely the contents of the fuse, after it exploded.  And you can test fuses, it only takes an Ohmmeter.  "Good" fuses have very low resistance (like way less than 1 Ohm).  "Bad" ones are open circuits!

If you actually blew fuses in the AL572 during tune-up, it sounds like you were tuning up waaaay too long, or weren't doing it right, or possibly both.  Correct and proper tune-up of the AL572 takes about ten seconds, if you're doing it slowly.  Once you're good at it, it takes more like five seconds.  If, during the tune-up process, the plate current exceeds a safe limit, you should be glad the fuses pop, otherwise you could easily damage the tubes, or the power supply, or both!

"SWR being a bit high" is _not_ responsible for blown fuses.  That is a certainty.  

WB2WIK/6
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KT4FD
Member

Posts: 4




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« Reply #2 on: February 25, 2002, 10:27:04 PM »

You're right - It was blown fuses.  And, again your probably right that I was tuning toooooo long.  

I replaced the fuses, and all is good to go.

I am having a probelm that i believe is with the tuner.  I can tune the rig with 100 watts to the tuner (MFJ-986), and SWR is 1:1.  However when I turn on the amp, and start to drive the exciter with very, very little power, swr shoots skyhigh !! From here, I cant even tune.  I think there may be a problem with the tuner?

Thanks for the help and input !!

Jim
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WB2WIK
Member

Posts: 20612




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« Reply #3 on: February 26, 2002, 01:04:40 PM »

Yep, sounds like a tuner problem, alright.  The MFJ-986, as well as it's cousin the MFJ-989, are notorious.

Check some of the product reviews on these, right here on eham.net.  They're not good.  

If you really, really need a tuner, consider something different.  I've had good luck with the Ameritron ATR-30.  Yep, I know Ameritron is part of the MFJ conglomerate, but this is a very different product.

73 & good luck!

Steve, WB2WIK/6
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KT4FD
Member

Posts: 4




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« Reply #4 on: March 01, 2002, 07:49:57 AM »

Steve, Thanks for you're input.  I received the ATR-30 yesterday.  All works very, very well!

Again, thanks!

Jim
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