2. amps-preamps
  3. 1207684029

Noise upon pre-amp tube replacement

I was replacing 7308 and 12AU7 tubes today (pair by pair) with newly purchased NOS tubes. They are RCA 7308 gold pins (made by Siemens) and Raytheon 5814. Each time I replaced the tubes, after 5 minutes I heard a "thump" from the left speaker as if a brick or wooden board fell down on the floor. I am wondering what it was? Has anyone experienced such phenomenon? My amp definitely does not like frequent tube rolling!
transl
thorman
1,262 posts
 
Once in awile you will get a NOS tube that doesn't survive the aging process..It could be a bad NOS tube..If you can flip the tubes from side to side ( left to right ) and the noise travels you have a bad tube...Its happened to me before so don't be too suprized if its a bad tube....
slates
35 posts
 
Hi Transl,
Thorman makes a good point, just be careful, I have seen some nos tubes short
out and cause some serious damage. When you buy NOS tubes always try to
get some warranty or at least have the retailer burn them in for 48 hrs.
If a tube fails , it usually happens within the first 48 hrs. If heard tubes go noisy
and microphonic before, and it is a shame with NOS tubes.
transl OP
156 posts
 
It was a single "thump" but then everything worked OK. There was no need even to swap the tubes from side to side.
More to discover