nevetslab
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- Dec 4, 2014
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I have a client's Dual Rectifier 3-Ch Solo Amp head on the bench, and besides it having a 15 Hz Oscillation in SS Rect Mode, which for the moment, I've removed the rectifiers (old version, 5U4GB's ALWAYS in circuit), Channel 1 in Pushed mode can be dialed up with a wide range of self-oscillation conditions...NOT just that mentioned in the manual (Gain at max, don't go past 2:30 on the Treble). Gain, Treble, Presence, Mid as well as Output & Effects Send Level controls all can affect affect this self-oscillation. Oscillation freq ranges from low-mid freq (200Hz) to beyond 20kHz. Nothing plugged in, 4 ohm speaker connected, Effects Loop In, controls at Normal, though it can also occur with Effects Loop Bypassed.
Swapped out V1 input tube, V4 Effects Loop tube, V2 2nd stage post-EQ tube. Switching out of Pushed mode seems to render it safe. I haven't pulled the main board yet. Looking for other posts from folks having had similar issues.
With regards to the LF oscillation associated with the 5U4GB's installed, if either Ch 2 or Ch 3 are selected, AND the voicing switch is changed to MODERN, it will kill the LF oscillation. Switch back out of it (Vintage, RAW), the LF Oscillation resumes.
Wierd!
Swapped out V1 input tube, V4 Effects Loop tube, V2 2nd stage post-EQ tube. Switching out of Pushed mode seems to render it safe. I haven't pulled the main board yet. Looking for other posts from folks having had similar issues.
With regards to the LF oscillation associated with the 5U4GB's installed, if either Ch 2 or Ch 3 are selected, AND the voicing switch is changed to MODERN, it will kill the LF oscillation. Switch back out of it (Vintage, RAW), the LF Oscillation resumes.
Wierd!