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Author Topic: 811h works/but doesn't work  (Read 490 times)
K0IYA
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Posts: 22




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« on: June 11, 2009, 12:53:09 PM »

A few days ago. I turned the 15 months old amp on, in 5 seconds, The Lcd lights, meters, manily everthing quit. Weither the power was on, opr. or HV/IP switches were on or off. Nothing seemed to work. Being hooked up to a  seperate tuner just to cross check power swr (I run direct on all ant. The amp was already loaded for 40m)The MFJ versa tuner III showed 650 watts out,(55watts drive) opr/ standby 50 watts. I made three short qsos. All with 59 plus reports.. Short, because the fan was not working. I unplugged the amp. Took precautions and found 1 tube burned out. I replaced the fuses which blew in about 5 seconds. I am guessing the IN4007 Diode was bad. I have ordered a pack of 12amp/250volt fuses, a couple chineses 811 tubes,(what Ameritron uses) and a few IN4007 diodes). First amp, I have worked on that works when broke.Any 811H experts or just know the amp fairly well, Have any suggestions. I have always been the type not to get the extended warrenty, but owning for 15 months makes me  question this attitude....Rob
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VR2XMT
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« Reply #1 on: June 11, 2009, 07:12:22 PM »

Rod,

I am not the 811H expert, but would like to share the experience which I learn before.

What you have described is probably the result of a tube short.  Check the 51 ohm grid resistors with an ohmmeter.  They are located on the left edge of the tube chassis.  If you find one of the resistors open, the tube in the same position is the cause of the problem.  

D16(IN4007) sometimes is shorted as the result of a tube arc. If D16 is shorted you will see much higher grid current and it will draw grid current when keyed with no rf drive.

For information, I replaced a total of 12 nos. of 811A in two years time, much worse than my toilet lamp. I no longer with this amp, move to SB-220 and TL-922. Good luck.

Charlie/VR2XMT
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