[Amps] a BANG in the AMP ?

[Ian White, G3SEK]

rlm wrote:
>
>On Saturday, October 18, 2003, at 04:52  AM, ON4MA Marc wrote:
>
>> When a switched on the commander 2500 a loud bang whas heard 
>>somewhere  in
>> the rfdeck.
>> The main fuse from the shack was out !
>> I got this amp cheap , look like never used.Before I switched on I 
>>did  some
>> inspection
>> inside.No dust ,tubes where in place (2x -3cx800a7) .
>> The guy who sold ,told me there was a problem on 10m and 80m .But other
>> bands where ok !
>> I emailed Pat at commander he told me to look in high voltage board.
>> Not so easy because you have to remove the rfdeck.My question is ,wat 
>>caused
>> the bang ?
>> bad tubes ?
>
>•  if the tubes arced internally, there would not have been a bang.

But an arc could easily have caused something else outside to go bang, 
for example splitting open a rectifier.

>
>> How could you check the tubes ?
>
>•  I would check them for leakage with a high-potential tester. and I 
>would also measure the resistance of each suppressor resistor by 
>unsoldering one end.  If a suppressor resistor is way higher in ohms, 
>my guess is that the tube took off on its own.
>
Took off, the moment he first switched on? 3CX800s have a three-minute 
warmup, so maybe not...


If you're doing a post-mortem, you have to look at the evidence as it 
*is*, not as you'd maybe like it to be.


-- 
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
                            Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek