[Amps] Amp Supply LK500ZB - strange failure mode

[k0zx Rich]

Agreed, that is the one thing i did do, is replace the zener, but no 
change. Looks like it is a bad tube, after swapping and pulling, the 
problem follows the one of them. So now for a little market research i 
guess.
Tnx
Rich
On 10/2/2014 2:05 PM, n8de at thepoint.net wrote:
> Sounds like a faulty bias zener.
>
> Don
> N8DE
>
> Quoting k0zx Rich <k0zx.co at gmail.com>:
>
>> Wonder if anyone has experienced this failure mode with this or a  
>> similar amp:
>>
>> This amp is 80s vintage and since then has been a solid performer,
>> grounded grid with two 3-500z. But it has a developed a problem where
>> at power up (no rf drive, ant relay input not active for tx), the plate
>> current rises to about 3x normal (about 300ma, 100 is normal), stays
>> there for 5 to 10 seconds and then drops to zero.
>> If enabled to transmit with  antenna relay input on, plate idle current
>> is normal, going from 0 to 100ma.
>> If apply rf in, it will output but at only about .6 or .7 its normal 
>> output.
>> After inspecting the schematic am not seeing an obvious source for the
>> problem.
>>
>> Any suggestions appreciated
>> Rich
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>
>