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I've just been finishing up a home-brew 6G15 reverb unit and encountered some issues a lot of folks seem to have with these.
The first is the one of the mixing circuit not giving enough control over the wet/dry signals. In other words it goes from nothing to too much too quick with not enough in between. The stock schematic calls for a 250K lin taper. A log pot would give a smoother transition here but since I didn't have one handy and didn't feel like installing it even if I did, here's what I opted for.
A 100K resistor across the outer legs of the existing pot. That's it. If you wish to experiment with different values it's simple enough to do with a pair of alligator clips - no iron needed until you find what you like best. 100K did the trick for my unit.
The second issue was dwell gain being too high and causing that awful fuzz- out distortion. I suspect this may be caused by the transducer coil on the tank being overloaded - but whatever the case is it can be remedied by lowering the gain of the input driver stage. You could lower the 250K pot to 100K or lower. Your bandwidth will change and you'll have a little more high end response which may be too much based on how the stock tone control is voiced. I opted for simply replacing the 12AT7 with a 12AU7 which gave me much better fine tuning and usable range with the ability to turn the pot to '10' with fuzzing out.
If the 12AU7 seems too weak for you, try a 12AY7. Its mu sits between an AT and an AU and it was always marketed as a lower microphonics/noise tube for sensitive applications. Whether it really has them may be another story.
This combination worked like a charm for me - with a minimum amount of hacking back into the circuit you worked so hard to complete.
Cheers
The first is the one of the mixing circuit not giving enough control over the wet/dry signals. In other words it goes from nothing to too much too quick with not enough in between. The stock schematic calls for a 250K lin taper. A log pot would give a smoother transition here but since I didn't have one handy and didn't feel like installing it even if I did, here's what I opted for.
A 100K resistor across the outer legs of the existing pot. That's it. If you wish to experiment with different values it's simple enough to do with a pair of alligator clips - no iron needed until you find what you like best. 100K did the trick for my unit.
The second issue was dwell gain being too high and causing that awful fuzz- out distortion. I suspect this may be caused by the transducer coil on the tank being overloaded - but whatever the case is it can be remedied by lowering the gain of the input driver stage. You could lower the 250K pot to 100K or lower. Your bandwidth will change and you'll have a little more high end response which may be too much based on how the stock tone control is voiced. I opted for simply replacing the 12AT7 with a 12AU7 which gave me much better fine tuning and usable range with the ability to turn the pot to '10' with fuzzing out.
If the 12AU7 seems too weak for you, try a 12AY7. Its mu sits between an AT and an AU and it was always marketed as a lower microphonics/noise tube for sensitive applications. Whether it really has them may be another story.
This combination worked like a charm for me - with a minimum amount of hacking back into the circuit you worked so hard to complete.
Cheers