I just purchased a second hand ARC CA50. The power tubes in the amp were EL34 instead of 6550C which was, ofcourse, undisclosed. Being a tube newbie, I wasn't able to recognize the power tube isn't 6550C. And, yes, there were electrical problems. $700 dollars later, I learned to stay with 6550C in ARC amps.
I also talked to numerous ARC dealers and Leonard at ARC. They all say using anything but 6550C is to be used at your own risk. The tech that serviced my amp was even more adamant. He claims every tube, driver, input and power, must precisely match.
I also talked to numerous ARC dealers and Leonard at ARC. They all say using anything but 6550C is to be used at your own risk. The tech that serviced my amp was even more adamant. He claims every tube, driver, input and power, must precisely match.