After running my bugle for a couple of years on 9v batteries, I decided to try upping the voltage to see if I could hear any improvement. Simply wired two 9v in series per channel. Tested voltage at 16.4v to the socket. Btw, upgraded 16v 220uf caps to 25v first.
Result - no sound. Low rumbling that doesn't change in strength when volume is turned up. Put single 9v in socket and full sound returns.
Any suggestions on what might be the problem?