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Ameritron 811 A problem

walter graves

New Member
Jan 14, 2022
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My Granddaughter pushed the auto tune button on my tuner while my 811a was in XMIT mode. Amp stopped putting out 500 watts and can only xmit 40 watts drive. checked fuses, replaced tubes with new. What could be Wrong. Thanks
 

Shockwave

Sr. Member
Sep 19, 2009
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Did you try it on any other band? Can you see what the input SWR is that the exciter is seeing? Does the amplifier draw normal bias current when keyed and no RF drive applied? Does that current go up normaly, when drive is applied? These answers will help determine the problem.
 
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nomadradio

Analog Retentive
Apr 3, 2005
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The calibrated eyeball is your friend. Any visible signs of heat stress will point either to a problem now, or a problem later.

A resistor burned in half indicates a severe surge current.

My intuitive guess is badly-weakened tubes. The 811A is quite unforgiving of severe overloads. A shiny spot at the center of the flat, gray anode in each tube indicates severe overheating. The kind that can damage a tube permanently. And if the surface of the metal was breached or has a hole melted in it, that tube can no longer be trusted.

Don't know how long she keyed it with a carrier on it. My intuitive guess would be that it was long enough to flatten the tubes, making them weak forever.

Kinda like draining the oil from your daily driver and heading down the street. There is no doubt there will be damage. How much and where depends on how far down the street you drove it.

73
 

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