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TSL-60 with vexing farting problem on all channels
Marshall TSL 60, 2005 vintage, with Issue 6 of the main PCB.
The saga of this amp started when another tech swapped out the cheap nasty DIN footswitch connector for a nice and robust XLR type. Afterwards, it farts when the master volume is raised above 3. I'm thinking this is a coincidence, as the new connector wiring all "beeps out" as it should.
C26 and C27 have been replaced with 1 kV parts (they had failed at some time earlier on) and C86 was changed at the same time.
Presence can be set at any level with no effect.
Pulling the feedback connection (W5 lug, from OT) kills the fartyness, but (big surprise) also affects the tone.
Disconnecting the presence circuit by pulling CON6 makes the fartyness far worse.
I've tried swapping out all the tubes, resoldering all the tube sockets, "retensioning" the power tube sockets, all with no effect.
Any ideas? I've attached a few scope plots.....
The saga of this amp started when another tech swapped out the cheap nasty DIN footswitch connector for a nice and robust XLR type. Afterwards, it farts when the master volume is raised above 3. I'm thinking this is a coincidence, as the new connector wiring all "beeps out" as it should.
C26 and C27 have been replaced with 1 kV parts (they had failed at some time earlier on) and C86 was changed at the same time.
Presence can be set at any level with no effect.
Pulling the feedback connection (W5 lug, from OT) kills the fartyness, but (big surprise) also affects the tone.
Disconnecting the presence circuit by pulling CON6 makes the fartyness far worse.
I've tried swapping out all the tubes, resoldering all the tube sockets, "retensioning" the power tube sockets, all with no effect.
Any ideas? I've attached a few scope plots.....
Attached Files