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09-05-2020, 05:27 PM
Hi Kevin,
I made sure the tube is fine - it's drawing 8,5mA at 285V, dissipating 2,42W.
I did think about lowering the gain on two first gain stages or running the signal through a voltage divider, but not in this particular build. Apparently my friend for whom I'm building it enjoys the amount of distortion he's getting by lifting the EQ. The unloaded signal still upsets the reverb driver tube and the oscillation even increases the preamp distortion.
The amount of reverb is just about right with the current V2 bias, but in my first build it's way too much at 10. I will probably be rearranging my own "AA1164" because I built it more for the clean tone and I definitely don't need that much reverb it now has. Actually I didn't suspect the 12AT7 driver tube was oscillating in it because the reverb sounds totally fine and there's no distortion in the wet signal. I can easily sacrifice the over the top effect for the sake of tube stability. I will probably incorporate some simple solution to cut down the signal on the V2 grid to a reasonable level when the EQ lift switch is engaged. The grid leak resistor could probably become switchable to a lower value and form an appropriate voltage divider with the grid stopper. I'm sure TUT will come in handy in this matter
I made sure the tube is fine - it's drawing 8,5mA at 285V, dissipating 2,42W.
I did think about lowering the gain on two first gain stages or running the signal through a voltage divider, but not in this particular build. Apparently my friend for whom I'm building it enjoys the amount of distortion he's getting by lifting the EQ. The unloaded signal still upsets the reverb driver tube and the oscillation even increases the preamp distortion.
The amount of reverb is just about right with the current V2 bias, but in my first build it's way too much at 10. I will probably be rearranging my own "AA1164" because I built it more for the clean tone and I definitely don't need that much reverb it now has. Actually I didn't suspect the 12AT7 driver tube was oscillating in it because the reverb sounds totally fine and there's no distortion in the wet signal. I can easily sacrifice the over the top effect for the sake of tube stability. I will probably incorporate some simple solution to cut down the signal on the V2 grid to a reasonable level when the EQ lift switch is engaged. The grid leak resistor could probably become switchable to a lower value and form an appropriate voltage divider with the grid stopper. I'm sure TUT will come in handy in this matter
