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Author Topic: 125v 12a slo blo for the al811  (Read 2169 times)
K9OJT
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Posts: 27




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« on: May 11, 2013, 09:35:24 PM »

My AL811 won't power up so I am guessing it is the fuses.

Where does one buy the 12 amp 125 v fuses for the al811? The Ameritron site doesn't list them as far as I can tell. They only list the 250 volt fuses.

Are there any replacements?

Thanks in advance.

Mike AC8IR
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K7MH
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Posts: 344




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« Reply #1 on: May 11, 2013, 11:31:28 PM »

It is not uncommon for the power switch to go bad so I would check that. Mine went recently.
Not certain but I think they are not slo blo fuses and are ceramic fuses instead of glass. If a fuse is blown you can check it with a multimeter to be sure, if it is a glass fuse it should be obvious. If one is blown then there may be a problem with the amp.
I think that Radio Shack has ceramic fuses of that value. I changed my AL-811 to 240V and used glass fuses as I couldn't find ceramic fuses of the right value locally. It had ceramic fuses in it when I got it but it was used.
« Last Edit: May 11, 2013, 11:39:38 PM by K7MH » Logged
KB1LKR
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Posts: 1898




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« Reply #2 on: May 12, 2013, 11:54:06 AM »

12A 250V would be an acceptable substitute for (uncommon?) 125V max rated fuses.
See Amertron P/N 75-1112-1, 12A 250V ceramic fuse
or Mouser P/N 504-MDA-12, 12A 250V ceramic
or Digi-Key P/N r   283-2723-ND, 12A 250V ceramic

Note higher max interrupt voltage rating are always acceptable, lower, ONLY if still above the actual voltage to be interrupted.
Ceramic fuses generally will have higher peak current interrupting capacity than glass fuses, and are less likely to shatter at high overload currents, but are a little more expensive than their glass counterparts, and may be the only type available in higher voltage ratings for higher rated currents (e.g. > 10A for a 1.25 x 0.25 [32 x 6.3] size).
I'd lean to name branded (Cooper-Bussman, Littelfuse, Shurter, etc.) fuses over brand-x from Radio Shack, but in a bind, the latter are better than being off the air.
 
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N6AJR
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Posts: 9921




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« Reply #3 on: May 12, 2013, 12:55:07 PM »

auto parts stores also still carry the "old style" tube fuse in 12 v ratings.
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N3QE
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Posts: 2356




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« Reply #4 on: May 14, 2013, 07:07:28 AM »

The 250V rated ceramic 12Amp fuse is what you want and what was originally in your amp if wired for 120V operation.

Also check the power switch, power cord, and the jumper block for transformer voltage selection. Those seem more likely culprits than the fuses.
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WX2S
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Posts: 744




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« Reply #5 on: May 14, 2013, 11:03:26 AM »

I just went through this with my Alpha.

Don't buy auto fuses. You want ceramic.

Ceramic fuses are sometimes called "microwave oven" fuses because of their common use. They are packed with sand so they won't explode if you put them in a dead short at 240v.

There are two sizes for the cartridge fuses, 5x20mm and 6.4 x 31.7mm. Make sure you get the right one.

Amazon has a lot of vendors who sell ceramic cartridge fuses. Here are listings for both sizes:

Bussman 12a 5x20mm ceramic slow-blow

Bussman 12a 6.4 x 31.7mm ceramic slow-blow

You can, of course, check the fuses in your amp by putting an ohmmeter across them. Zero ohms is good.

73, -WX2S
« Last Edit: May 14, 2013, 11:12:35 AM by WX2S » Logged

73, - Steve WX2S.
I subscribe to the DX Code of Conduct. http://dx-code.org/
KB1LKR
Member

Posts: 1898




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« Reply #6 on: May 14, 2013, 06:23:09 PM »

Also, don't buy automotive fuses for line voltage applications as they're generally 32V not 125 or 250V rated!
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K9OJT
Member

Posts: 27




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« Reply #7 on: May 18, 2013, 07:09:01 PM »

Thanks to all those who replied to my original post.

Yes, the fuses were blown, but for good reason.

I pulled the cover and found a bad tube. I removed the little bugger...replaced the fuses...put the cover on...and (YIPPEE!!) power with no blown fuses.

Now comes the big decision. Replace the fuses with 811As or opt for the 572Bs. If stay with the 811A fuses I will have two spares...with the 572B fuses I won't.

If anyone has additional input please feel free to post it. I am at least the third owner of this amp and it was purchased as a starter amp. Better to cut one's teeth on something less finicky and cheaper than a higher priced amp. When it works, it operates gangbusters, just not at the this present moment LOL!

I going to Dayton on Sunday. Does anyone know if the vendors bring replacement tubes with them? I know this is short notice, but I am just tossing it out there in case someone knows.

Once again...thanks for the excellent replies.

73

Mike AC8IR
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