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Author Topic: Fuse blew on Amertitron 811  (Read 5192 times)
VA3KBC
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« on: December 04, 2012, 06:38:46 PM »

Well she let me down tonight. Blew the 12amp ceramic fuses and I replaced them with 15 amp glass fuses. Blew both of them, so...something is amiss.
Either power supply or cap, or tube?

emailed my friend to see if he can look it over along with my Dentron Clipperton L.
Then the Dentron will go for sale, and I'll keep the Ameritron 811 as my main amp.
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W8JX
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« Reply #1 on: December 04, 2012, 07:09:07 PM »

My guess is a shorted tube. If it was a bad cap it usually will smell some.
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K8AXW
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« Reply #2 on: December 04, 2012, 08:35:42 PM »

Make sure the HV is bled off and the amp is unplugged and then remove the tubes and try it again.  If it still blows fuses, then you probably have a power supply problem. 
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K4RVN
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« Reply #3 on: December 04, 2012, 09:10:54 PM »

I own the three tube AL 811 and agree about pulling the tubes for a starting point, and being careful to make sure the amp is unplugged and HV is zero.
Also read your manual on how to remove the 811A plate caps as it is easy to break the tube caps  if not done right. The plate caps are tight and Ameritron gives specifics on removing them.

Frank
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AA4HA
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« Reply #4 on: December 05, 2012, 05:32:49 AM »

I would really advise against upsizing the fuses while troubleshooting. You know that there is some sort of fault and repeatedly "pranging" the power supply while attempting to isolate the problem might cause you much bigger problems.

Pulling the tubes is a great first start.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
KE3WD
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« Reply #5 on: December 05, 2012, 05:44:04 AM »

I would really advise against upsizing the fuses while troubleshooting. You know that there is some sort of fault and repeatedly "pranging" the power supply while attempting to isolate the problem might cause you much bigger problems.

Pulling the tubes is a great first start.

Pay heed. 

Luck of the draw, that could have been a di$a$ter. 


73
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WB7TXG
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« Reply #6 on: December 05, 2012, 08:02:37 AM »

There are others that know much more than I but Ive been where you are at...
remove AC and make sure caps are discharged
remove cover case.. lots of screws
Use bright light and visually inspect grid caps and resistors underneath each tube socket.. look very closely
Most likely tube filament shorted and blew one or more of the caps and resistors on tube sockets
If damage found there are some great links with pictures to help you repair....
You will also of course need to replace the tube or tubes that caused the problem..
This might not be where problem is but Id sure start there first
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KE3WD
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« Reply #7 on: December 05, 2012, 08:06:44 AM »

Tubes are not the only component that can cause excessive current draw. 

Rectifiers, for one, are another, and a diode junction can fail just as quickly if not actually even faster.

Whatever, this amp must go on the testbench and troubleshot in a safe and thoughtful fashion to find out what failed.


73
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W8JX
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« Reply #8 on: December 05, 2012, 09:08:57 AM »

Tubes are not the only component that can cause excessive current draw. 

Rectifiers, for one, are another, and a diode junction can fail just as quickly if not actually even faster.

Whatever, this amp must go on the testbench and troubleshot in a safe and thoughtful fashion to find out what failed.


73

The AL811 amps biggest "weakness" is its tubes in that when you run amp at "rated" output you are basically exceeding limits of tubes. It is easy to fry tubes with a full power tune if you are not very quick about it. While it is a popular amp because of price it is also one prone to failure because due to them being run harder than they should be. While there may be a problem in power supply I have little doubt that it has at least one bad tube that is shorted which can damage power supply too. Also as someone mentioned earlier, installing bigger fuses is never a solution to a problem like this and can make matters worse.
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VA3KBC
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« Reply #9 on: December 05, 2012, 10:03:35 AM »

Thanks everyone. I realise that trying the higher amp fuses is a nono, but it was all I had and was going to hit the off switch if the factory smoke was starting to find it's way out.

One thing I remember doing that morning ....well feel dumb telling everyone...but I was going between my 160 off center dipole and the tuner and my 80 meter resenant antenna. I have a DX engineering 8 position switch so it was just a mater of switching from 160 to 80. Turn switch on AT1500 tuner and hit the tuning pulser. I was running 30 watts on the TS590. Then when I had the tuner tuned I put the power up to 100 watts to check the swr again on both 160 and 80.
Listened for a bit then went to 160 and took the standby switch off on the amp. Keyed up and talked for 10 to 20 seconds, before I realised the exiter was at 100 watts instead of at 30 watts....see I ain't the sharpeest kkniffe in the drawwerr.

So later that evening when I turned everything on...nothing from the amp. That's when I blew the fuses.
Long story short I caused my amp to go south with dumb testing and being forgetfull.
I usually double check these things when I do testing between antennas and such, but for whatever reason I screwed up.
Leason learned. I also just recieved and email from RF Parts for the 572B-M3-TAY tubes. $209.70 shipped here to my location in Canada. Sad 
From reading info on K8JI's site it may pay to go with the better Talyor 572B's

73, DJ
VA3KBC
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VA3KBC
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« Reply #10 on: December 05, 2012, 10:21:12 AM »

Has anyone with a TS590 hooked up the ALC to the amp?
I was told this would have prevented my over running the power.
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WX7G
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« Reply #11 on: December 05, 2012, 10:58:34 AM »

I would not bother with 572B tubes in the AL-811. 811A tubes are all that is needed.
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VA3KBC
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« Reply #12 on: December 05, 2012, 11:23:07 AM »

The 811A Taylor Select matched set of 3 is $67.35.
Getting 2 sets is still cheaper than the matched set of 872B's at $164.70.

Well I talked to a local ham here and he said to bring it over for him to check it out.
That's my next step.
73, DJ
VA3KBC
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N4CR
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« Reply #13 on: December 06, 2012, 08:13:39 AM »

Getting matched tubes for a non push-pull amplifier is a waste of money.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
VA3KBC
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« Reply #14 on: December 06, 2012, 12:26:12 PM »

Here is what my friend sent me.

"Two of the tubes were no good one the tube checker did not like"

After a lot of reading and second guessing myself I decided on the Taylor 572B's from RF-Parts. I decided to go with what the majority have said was the way to go. My choice was to get the most out of what I have and Bill is also change the amp to 240volts.

I have also ordered from DX Engineering the Ameritron 240V inrush current protector and the AMP amplifier relay /alc cable.

73, DJ
VA3KBC
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