Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 1blueheron on October 15, 2018, 02:16:44 pm

Title: Scratchy sounding 6SL7.... tube or amp?
Post by: 1blueheron on October 15, 2018, 02:16:44 pm

I ordered a new JJ 6SL7 to go in the Webster amp that Sluckey helped me modify.  I have been running it with a 6SN7 in that socket and it has worked perfect and been dead quiet.

Well, the new 6SL7 came Fri. and I put it in its position with great expectations.   Turned it on and it sounds like someone playing a scratchy record or tuning in a radio.  Lots of hissing and scratching.  No real pops, more like intermittent white noise at various levels.  Put the 6SN7 back in and its dead quiet again.

I plan to swap positions between 6SL7's tonight and see if it makes a difference but I am thinking they sent me a bad tube. 

Any thing I can do to definitively determine it is not the amp ar that would say for sure it is the tube?  I don't have a tube tester.

Title: Re: Scratchy sounding 6SL7.... tube or amp?
Post by: sluckey on October 15, 2018, 02:27:19 pm

Quote

I plan to swap positions between 6SL7's tonight and see if it makes a difference

do that

Title: Re: Scratchy sounding 6SL7.... tube or amp?
Post by: shooter on October 15, 2018, 04:48:49 pm

Also, you might let it "cook" for 24hrs or so, The last 3-4 AU7's I bought new were really sketchy but after about 20hours of "variations" each has settled down to "known good, tested"

Title: Re: Scratchy sounding 6SL7.... tube or amp?
Post by: John on October 15, 2018, 07:43:37 pm

Quote

hissing and scratching.  No real pops, more like intermittent white noise at various levels.

I love 6SL7, but that sure sounds familiar.

Title: Re: Scratchy sounding 6SL7.... tube or amp?
Post by: terminalgs on October 16, 2018, 07:22:55 am

Quote from: 1blueheron on October 15, 2018, 02:16:44 pm

Lots of hissing and scratching.

try a AC signal ground on the grids, if the noise goes away.  with something like this,  one side to ground, the other to grid:


(https://i.imgur.com/pI8zwEdm.jpg)


capacitor can be .0.5uf or bigger.  if its a gains stage with 0vdc on the grid, you can just ground the grid. 


I'd get ready to return the 6SL7.   if you didn't hear any noise with the 6SN7, but you do with the 6SL7 then probably a crummy tube.  If you heard the same noise, only it was quieter with the 6SN7, that's a different story...