NEW> 811 h rf feed back - Amplifiers Forum at eHam.net

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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

RE: NEW> 811 h rf feed back	Reply
by W5DQ on April 2, 2009	Mail this to a friend!
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

RE: NEW> 811 h rf feed back	Reply
by N4ZY on April 2, 2009	Mail this to a friend!
thanks for reply. as usual i think i am operating in good maner. but old dogs CAN learn new tricks

RE: NEW> 811 h rf feed back	Reply
by K6AER on April 2, 2009	Mail this to a friend!
“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.

RE: NEW> 811 h rf feed back	Reply
by WB2WIK on April 2, 2009	Mail this to a friend!
>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

RE: NEW> 811 h rf feed back	Reply
by W7ETA on April 2, 2009	Mail this to a friend!
"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

RE: NEW> 811 h rf feed back	Reply
by K6AER on April 3, 2009	Mail this to a friend!
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

RE: NEW> 811 h rf feed back	Reply
by N4KZ on April 3, 2009	Mail this to a friend!
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

RE: NEW> 811 h rf feed back	Reply
by N4ZY on April 3, 2009	Mail this to a friend!
ET ALL/ thanks for all the feed back. Story== i have been useing this amp for almost a year with this rig.no problems. sometime a flakey loading of the amp but restarted and all was fine. antennas all check A ok. while i was tuneing up to work a VK9. crap hit the fan.meters on the amp went crazy . also the meter on Pro 3 did likewise.shut all down PDQ. powered up the Pro 3 after checking all connections.found that the pro 3 output was 35/40 watts max.swr has never been a issue. talked to a Icom repair Center. the first words out of their was to get rid of the 811h.that it usualy the factor in such things. set it to repair man. he called and said same thing .that the amp was the cause of my demise.i thought i might have a relay problem that cause it. but was told that it was a RF Feedback that caused it.NOW,i have ran this amp as i stated for a good length of time .worked a bunch of good DX.SO am at a loss at where to start. the rig is being repaired BUT i am Gun shy about the amp.i might also add,that even tho Pro 3 output was 35/40 watts it would drive the amp to 450 watts. LOST IN Space(LOL) Jim N4ZY

RE: NEW> 811 h rf feed back	Reply
by WB2WIK on April 3, 2009	Mail this to a friend!
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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