Hi Ulf,
Thanks for the reply. Unfortunately this the C4-15D, not the C4-7 I was inquiring about. The C4-7 is the one and only tube for the Photogenic head I have. I have communicated with Photogenic and was told that they discontinued this flash tube more than 5 years ago. They also sent a name of someone to get in touch with at a Photogenic Service Center, but I haven't had an opportunity to follow up on that at this point.