2. tech-talk
  3. 1404598134

Help on tube question

Is it possible to replace a bad kt88 tube with a 6550c tube and do no damage? The VAC 160i uses 4 KT88's and with one of the tube bad, I have lost one side of sound. If it were ok to use the 6550c's, I could replace the 4 KT88's or just one. I know Monday I will get help from VAC. But, I just want to hear that sound again if I could and do no damage.
Thanks for any information or Opinions. Tra
Ag insider logo xs@2xtradubois
rodman99999
6,032 posts
 
The Sigma 160i is designed with KT88s in mind(specifically),
and offers no tube type selection switch(unlike the PA160).
You may not be able to properly bias a quad of 6550s.
I would strongly recommend you not try to replace just one
tube with a 6550 either. If you do try the 6550s, watch the
plates, while trying to bias, and if they glow red, STOP!
imo: Best be patient.
plasmatech
77 posts
 
Replace the 4 KT88's. Be safe and do what VAC recommends.
mercury3
3 posts
 
I had an Audio Research Classic 60 with KT88's kept failing now and then. I replaced them all with 6550's and never had another tube failure as long as I owned the amp which was about 20 years. Could just be my bad luck but I've never been comfortable with KT88's ever since.

But yeah the tubes need to match. Don't mix a 6550 with the KT88's. Just replace them all I think.
More to discover