Hm, have another strange problem. Sometimes, and completely unpredictable, the amp goes crazy. As you might see I have fast blow fuse in anode line and seldom plate current rises to some crazy volume. In a past I have cooked my Chinese tube:
http://www.goodsoundclub.com/Forums/ShowPost.aspx?PostID=10426
and I was under impression that I “crewed something up”. What I did not say in the referred post is that I did not fixed the problem but the problem is gone itself. I was frustrated particularly because the problem bitten me by my paw, returning recursively rarely. So, I put the fuse and it protected my tube, still I had no idea what it was. I checked all assembling 6242 times but nothing that I recognized was wrong.
This morning it happened again, and did not go away before burned a dozen fuses, then it went away after I did absolutely not relevant change. So, if there were no structural changes done that cured the problem then it shall be internal fault of elements. My investigation shows that the 185V of cathode voltage get shorted to ground, the question is where? I was checking everything and looks like fine.
What came to me this morning is that it might be the filaments of my 6 drivers tubes or 2 power tubes (1/2 6C33C) might shortened to ground. Since I lifted the center tap of my 6,3V supply my filaments are flooding and have pass to ground across the DH resistor. That is 180V between filaments and cathode. Would it be possible that some of the filaments sometimes break through?
If so, then I would need to put another transformer in game, but I wonder how can I confirm it… |