I have a new Hartke 3500 bass amp and am considering switching preamp tubes . Is there a risk factor in switching the stock 12AX7 for a JJ Tesla ECC803s? If an increase in gain and power results from the preamp, would this pose a danger to the power amp or othe circuitry? If this is a reasonably safe mod, how would I open the chassis on this one? What would I read to catch up on bass amp theory?