Hello,
I had my Tubelab SE (300B) for more than 4 years without any problem. Tonight, I was setting the bias on the right channel via R18 (about 65ma) when my voltage meter lead slipped and a spark occurred. Right after, I cannot measure any current on R18 and no music is flowing on the right channel. I turned the amp off and switch tubes, I thought I killed my right channel 300B but after switching, still the right channel is dead with music on the left.
All tubes are glowing. R18 and R29 measured at 10 ohms. No music on right channel. Did I kill my right channel mosfet (Q1)? Thanks for helping.
I had my Tubelab SE (300B) for more than 4 years without any problem. Tonight, I was setting the bias on the right channel via R18 (about 65ma) when my voltage meter lead slipped and a spark occurred. Right after, I cannot measure any current on R18 and no music is flowing on the right channel. I turned the amp off and switch tubes, I thought I killed my right channel 300B but after switching, still the right channel is dead with music on the left.
All tubes are glowing. R18 and R29 measured at 10 ohms. No music on right channel. Did I kill my right channel mosfet (Q1)? Thanks for helping.
So you measure B+ on both sides of R18? What about the tube plate? Best to check just to verify that the OPT is OK. Aside from that, yeah it sounds like you may have killed R34 or the FET. You might also want to look carefully at the PCB traces. Take some measurements on both sides of R34 to see if the bias voltage is there and that it changes when you turn the pot.
Where was the probe when it slipped? Do you have clip leads?
Where was the probe when it slipped? Do you have clip leads?
Yeah, if you have B+ on the plate of the 300B, you know your OPT is OK. it probably is, but you never know. Since you saw a big spark, I'm assuming the DRV jumper (with B+ on it) shorted to R34. If you shorted B+ to the FET side of R34, I wouldn't expect anything bad to happen unless the back-EMF killed the FET. So I'm left to wonder if the shock simply popped R34 itself.
Hi Russ. Thanks for your help. I think I got it. Preliminary measurements are all good. I replace Q1, Q2, U1, U2 and both the 100k pots. I was able to measure 175 volts on the plates of 5842s and 65ma on R18 and R34. After 5 minutes of being on, the amp retained all the measurements mentioned. I'm happy but the problem is that by replacing all those parts, I cannot pinpoint what was the culprit originally. Thanks again, Sir. Godspeed.
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