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
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