This is an instrument tube preamp utilizing four (4) 12AX7s and one 12AU7 tube.
We think it has an intermittent something some where inside. It cuts out in the middle of a set. Usually the third or last set of the night. Just enough to ruin any trust in this pre-amp. So it I took a look at it for my good friend a bass player.
After burning this unit for many hours over many days and tapping around the unit I observed two possible intermittent items. The power cord receptacle on the rear chassis or the female plug end or the front panel input jack. The power did not come on when I first plugged in the rear power cord connector. I fussed with it for a minute then it has not failed since. The other possibility was a dirty 1/4 inch front panel input jack.
I cleaned all the connectors and pots. Then I set about testing the tubes on a Hickok tube tester. All tube tested good and above GM spec.
I decided to replace the input and two output connectors. They get the most abuse. I do not like the weak tin material they are made of. I suppose the original plastic and tin made for easy installations. But I prefer the good old silver plated heavy duty (commercial grade) Switchcraft connectors.
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