soundsactive
Well-known member
i'm currently rebuilding a 140b that was a literal rats nest. it's all almost working again (yea!), but i am running into a problem without the output signal.
basically, it's too loud! the level control is set at it's lowest, and still it's a little distorted. it looks like the problem is at the output transistor, tr72. emitter is measuring -.6v (instead of -0.06v), base is -0.7v (instead of -0.09v), and collector -33.3v, which is fine. all transistors have been replaced with new ones from vintage vibes. The level control pot has been tested and looks pretty ok, as is the volume knob. tr71 is a bit high on emitter at 33v, and base, at 32.9v. overall, it's all pretty close considering it's a 50+ year old schematic.
the ldr has been upgraded to an LED, which also hasn't been as rich of a vibrato as a 140b with a incandescent. i assume that part of the problem is coming from this part of the circuit. it's at a beautiful volume and no distortion when the led is not in place and the LDR is uncovered to receive natural room light. is there a good source for the original incandescent bulbs out there?
basically, it's too loud! the level control is set at it's lowest, and still it's a little distorted. it looks like the problem is at the output transistor, tr72. emitter is measuring -.6v (instead of -0.06v), base is -0.7v (instead of -0.09v), and collector -33.3v, which is fine. all transistors have been replaced with new ones from vintage vibes. The level control pot has been tested and looks pretty ok, as is the volume knob. tr71 is a bit high on emitter at 33v, and base, at 32.9v. overall, it's all pretty close considering it's a 50+ year old schematic.
the ldr has been upgraded to an LED, which also hasn't been as rich of a vibrato as a 140b with a incandescent. i assume that part of the problem is coming from this part of the circuit. it's at a beautiful volume and no distortion when the led is not in place and the LDR is uncovered to receive natural room light. is there a good source for the original incandescent bulbs out there?
