I built a Crack/speedball for my son a couple of years ago. He recently moved from the east coast to the midwest and upon arrival put the crack back into his system. He then noticed it wasn't working even though at least the small tube was glowing by his report.
After some back and forth he asked if the big tube had to be placed in its socket in a particular way. We discovered that he had forced the tube - a Russian 6N13S into the socket the wrong way.
When he corrected the error and placed the same tube correctly - the Crack was back playing music.
