|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
91.76.167.78
I installed a pair of Sylvania 6SN7GT/VT-231 tubes in my amp. The tubes were purchased as NOS from a reputable dealer several years ago. One of the tubes instantaneously produced a very loud low frequency hum, which means that it is faulty. I wonder what could be the reason for such failure, if the tube was kept in a drawer for several years. The same thing happened earlier with one of JAN GE 6550 tubes and one of Siemens/RCA 6922 tubes.
Follow Ups:
Did you ever play with the global negative feedback in this amp?
No, I didn't. I just don't know how to do it.
Only three or four of approx. 50 tubes in my stash behaved like that. I wonder if they might have lost vacuum during storage - I mean, may it happen in principle?
I can't remember any which have lost vacuum sitting in storage.
I used GE 6550s from time to time in Cary SLI-80, then put them into storage, and when I installed them again later, one of them produced hum (GE 6550). I threw it away yesterday.
One of VT-231s was probably faulty from the start, though I am sure that the seller tested all of them before shipment.
The likely cause of your hum (based on your description) is heater to cathode leakage. If you have AC powered heaters the leakage can induce a hum in the tube.
Try running the tube for a few hours then let it cool and check it again. And be sure the base and pin area is VERY clean.
Go see if the GE you tossed out is retrievable too - it's definitely worth saving!
Likely a cathode to filament short.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: