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-   -   blown 2sj201 and 2sk1530 (https://www.diyaudio.com/forums/solid-state/192454-blown-2sj201-2sk1530.html)

kees52 11th July 2011 09:42 PM

blown 2sj201 and 2sk1530
 
Hi There


I was busy with upgrade the hybride amp with a new better tube in the driver sectie, but this tube ging some high with his bias and my mosfets did blown because the idle current went to high because of that tube, normally mosfets don,t blow if the idle current go to high, I have fuses with dit also blow because of that mosfet problem.

The mosfets are shortcircuit between gate drain and source, both.

Maybe someone have a clu why, I had gate protection diodes mounted and the amp was already desing be my 3 years ago.

NOW I NOW TO REMOVE THE FUSES IF THE TUBE IS CHANGED, PUT BACK FUSES IF TUBE IS PROPERLY BIASED, THAT i WAS FORGOTTEN.

The tube is dc coupled with the fets, and the tubes has one CCS and a tube on 2 x 120 volt.

Normally is idle for the driver tube is 35 ma but it go to 70 ma, therefore the idle current of the fets went to high and the fuse blow out, later seems the fets are also defect both ones, that is a strange matter, fets come from ebay maybe I has bad ones, who known.

sone tips for preventing welcome.

kees52 13th July 2011 11:10 AM

I have found that the ground (null) from the tube supply was broken, bad solderjoint, and so th current source has go flipped out cause a large current and a high voltage to the gates of the mosfets, nice is that the 2sj201 and 2sj1530 have more sensitivity for gate breakouts, the older ones from hitachi don,t blow stil working after fuses blown out, I have gate protection diodes used with the 2sj201 and partner but not with the hitachi ones (2sk1058 and 2sj partner much stronger and good for tests).


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