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Author Topic: NEW> 811 h rf feed back  (Read 930 times)
N4ZY
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Posts: 81




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« on: April 02, 2009, 03:23:26 PM »

i have been told that RF feed from my 811H with 572b. tubes cause a catastrophic force(big word)that wiped out the pa units along with other items.on my New Icom 756 pro 3. and have been instructed by the VOICEof Icom to get rid of the 811h. i ran a 811h to a 756 orignal for 5 years no problem. never used alc cabel or buffer relay. i run only 1 radio to the 811 h thru a rcs-10 to 5 antennas. dont know where to begin.
                           Jim N4ZY
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W5DQ
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« Reply #1 on: April 02, 2009, 04:06:46 PM »

Not sure where you should begin. My first thought would be get rid of the ICOM, but of course, that is just my opinion. I run a AL-811 (3 tube version) with 572B, currently on an older Kenwood TS-940SAT with no problems what so ever. Note that I do use the Ameritron relay/ALC breakout box ARB-704. I have also used this on a Kenwood TS-440SAT (again with the 704 option).

It may have been possible to have enough feedback to damage the xcvr but I would find that puzzling if the AL-811H was run IAW the manual.

Good Luck in figuring out the solution. Post what you find for others to know.

Gene W5DQ
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Gene W5DQ
Ridgecrest, CA - DM15dp
www.radioroom.org
K6AER
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Posts: 3535




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« Reply #2 on: April 02, 2009, 06:54:53 PM »

“RF feed from my 811H with 572b. tubes cause a catastrophic force(big word)that wiped out the pa units along with other items on my New Icom 756 pro 3.”

Some questions come to mind;

•   That is quite a statement. Just what was the failure mechanism?

•   Did high voltage some how make it past blocking caps? Not likely.

•   Were the finals destroyed from High VSWR and why did the radio not fold back? The IC-Pro-III has a very aggressive fold back circuit.

I have never heard of an amplifier destroying the finals in a driver transceiver when connected properly.

By any possibly???,  did you connect the transceiver to the amplifier output connector and key the transceiver and amplifier, tuning the output caps. You might have excited the amplifier finals and they would have coupled back into the transceiver finals. If this is the case the radio is not the problem.

As they say in Flying, cock pit error led to the crash.
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WB2WIK
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Posts: 20666




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« Reply #3 on: April 02, 2009, 09:11:36 PM »

>NEW> 811 h rf feed back  Reply  
by N4ZY on April 2, 2009  Mail this to a friend!  
i have been told that RF feed from my 811H with 572b. tubes cause a catastrophic force(big word)that wiped out the pa units along with other items.on my New Icom 756 pro 3. and have been instructed by the VOICEof Icom to get rid of the 811h. i ran a 811h to a 756 orignal for 5 years no problem. never used alc cabel or buffer relay. i run only 1 radio to the 811 h thru a rcs-10 to 5 antennas. dont know where to begin.
Jim N4ZY<

::Be more cryptic?  Okay, only kidding.

Who at Icom told you the amplifier damaged the rig?  That's quite a bold statement, especially if it was over the telephone and they hadn't seen the rig or the amplifier.  Or, have they seen it and it's now in their shop?  You didn't tell us the "whole story," and being part Russian, I love long stories, so let us know...

WB2WIK/6  
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W7ETA
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Posts: 2527




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« Reply #4 on: April 02, 2009, 09:30:26 PM »

"dont know where to begin."

Same amp, basically same rig but with some updates.

I'd be puzzled too, especially if they can't explain why the same model rig could go SK when it replaced it self.

73
Bob
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K6AER
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Posts: 3535




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« Reply #5 on: April 03, 2009, 06:44:17 AM »

Steve,

I did not know you had Russian in your blood. Next time we are together we’ll eat something other than Italian like Beef Stroganoff with a Georgian Wine.

Mike
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N4KZ
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Posts: 605




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« Reply #6 on: April 03, 2009, 06:55:29 AM »

I successfully ran a Pro3 and AL-811H for five years without one minute of problem. They were very compatible. I see no reason to get rid of either.

73, N4KZ
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WB2WIK
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Posts: 20666




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« Reply #7 on: April 03, 2009, 08:19:17 AM »

Mike, yeah, my Dad's parents were from Russia.  Unfortunately they were quite old when I was young so I didn't get to know them all that well.  But they taught Dad "Yiddish," which is still useful in parts of Brooklyn, Miami, etc.  ;-)

Regarding the amp: Now we have more of the "story," thanks.  I *sounds* like what may have happened is you developed an 811A short and energy was dumped back through the tuned (cathode) input circuit to the Icom (or any rig that would have been connected to it), damaging its PA stage.  That's not "RF feedback," exactly.  If that happened I'm surprised the fuse in the 811H didn't blow very quickly, but then we don't know the exact nature of the failure.

I haven't heard of this happening before with an 811H or really with any of the Ameritron amplifiers.  I do subscribe to the "amps" reflector and there's amplifier chit-chat on there every day about every kind of failure under the sun, and I haven't heard of this one before.  I suspect it's a rare thing.

Maybe Tom W8JI will chime in on this, I think he designed that amp.

WB2WIK/6

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K6AER
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Posts: 3535




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« Reply #8 on: April 03, 2009, 04:05:03 PM »

While making sure the amplifier is unplugged and the HV choke is shorted to ground after the voltage on the HV meter reads zero…..

•   Check the TR Relay with an ohm meter to make sure your contacts are good.

•   Look for a band solder connection on the coaxes.

•   Look for loose hardware in the input matching circuit.

•   Make sure the band switch is aligned for the input pi networks and the output band switch.

•   You are not blowing fuses so the tubes are probably OK.

•   If all is ok in the amplifier then check your connecting XCVR coax for a bad connection.

•   If all is OK from the above, then drive the amplifier with 40 watts to see if it performs. It should give you about 400 watts out PEP on SSB.

Look at the VSWR meter on the Pro-III to make sure you don’t have reflected power coming back.

Only then would I increase the drive to the recommended level for full output.

On another subject, make sure you Pro-III is clean inside and well ventilated. The radio can build up heat and if the vents get dirty the air flow is restricted and the radio will overheat. The finals could die prematurely if they get too hot. I have added a three inch muffin fan to the rear of my Pro-III just to make sure it stays very cool. As a result the internal fan never comes on.

Good Luck
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KG6UGS
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Posts: 12




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« Reply #9 on: April 13, 2009, 02:26:54 PM »

Please would some one please help me , I just recieved my AL-811 and I need to know how to set the PLATE and LOAD dials, This is my first amp.
Please make it simple for me as my age has taken over my mind.
Thanks Guys
Jack  KG6UGS
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WX7G
Member

Posts: 6328




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« Reply #10 on: April 13, 2009, 03:13:00 PM »

Have you got the Icom set up to delay the RF for >15 ms after the amplifier TR relay command?

During relay switching there is a brief period where the transceiver is not connected to anything.

Before purchasing my AL-811 I read all of the eham reviews of it and the AL-811H. I don't recall mention of the problem you describe.

Perhaps the operative word in your post is 'new' Icom. Could this failure be infant mortality that Icom is blaming on the amp?

I think that Tom, W8JI did a superb job desiging the AL-811 and AL-811H amps. They both are a lot of amp for the money.
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