Agree with Jfrech - it's a tube (or tubes in the case of the other set). I just retubed my VK-3i with NOS tubes from Kevin Deal at Upscale Audio and it sounds wonderful. I got 4 Phillips platinum grade PCC88/7DJ8's for $35 each and 2 Pope 6V6GT's at $49 each.
I'm sure other reputable tube sellers are good too but Kevin has always been very helpful. - Dick
I'm sure other reputable tube sellers are good too but Kevin has always been very helpful. - Dick