2. amps-preamps
  3. 131894-1659

Biasing signal tubes on a tube power amp/Quicksilver M120

Took possession of a new pair of Quicksilver M120 power amps with the KT150 tube upgrade a few weeks ago, am in the process of break in with about 70 hours so far. About 30 hours in I noticed that a 12AU7 tube had started to flare up when that amp was turned on so swapped that tube to the other amp and it followed the tube, I contacted Quicksilver and he told me that this is not a concern but to please switch that tube back to it's origional amp as the amp was biased for that specific tube, now my question is if I wanted to tube roll these 12AU7 or 12AT7 tubes am I out of luck and what happens when it is time to replace them as they wear out, are my tube rolling days over or are they just limited? What say you?
tooblue
13 responses Add your response
audioconnection
1,015 posts
 
Many 12Au7 types have this flash on turn on.
 No concern.
  Just make sure you check the bias when you swap in any new tubes.
Quicksilver Great company you should enjoy for many years.
 
 Best,
JohnnyR
 Audio Connection
Quicksilver dealer
tooblue OP
787 posts
 
@audioconnection , I am really liking the amps but still a bit confused as to the biasing of the smaller tubes, the power tubes are no problem biasing but I am not aware of the process to bias the smaller tubes.
yogiboy's avatar
yogiboy
2,678 posts
 
The smaller tubes are not biased. You can replace any tube with any brand that you choose. Just make sure it is the same type of tube!
tooblue OP
787 posts
 
@yogiboy , thank you , that is what I thought but did not know for sure.
tubegroover
2,279 posts
 
Enjoy those amps tooblue, if they have the same sonic characteristics, with more power being the difference as the silver 88’s I am happily listening to, you are in for a real long term treat. I have owned many tube amps through the years but the Quicksilvers REALLY hit all the right notes, very special, especially in light of what you get for your money.
tooblue OP
787 posts
 
@tubegroover , I am replacing a pair of VTL MB125s that are 21 years old, would have replaced with a like set but were out of my pay grade and took a chance on these, am very happy, just really hate break in time but so far have already showed themselves to be keepers.
glennewdick's avatar
glennewdick
702 posts
 
You may want to double check as I do believe i read in another thread that the QuickSilver amps do need the small signal tubes biased when replaced, also if quicksilver told you to put the original tube back into the original spot in the original amp because they biased it for that spot then it would indicate to me that they are biased. I do know many(most) tube amps do not need the small signal tubes biased but you may want to double check, and i'm sure your dealer can do this work for you.
tubegroover
2,279 posts
 
There is no biasing required for the small signal input and driver tubes. 



seikosha
205 posts
 
There is nothing in the manual for that amp about having to bias the input tubes.  Perhaps the output tubes would need to be biased when the input tubes changed and that's what Mike was referring to.
audioconnection
1,015 posts
 
   (((You may want to double check as I do believe i read in another thread that the Quicksilver amps do need the small signal tubes ))

  Balance adjustment for the small tubes should be done by a tech
  using DC voltmeter.
 Best JohnnyR
   
tooblue OP
787 posts
 
@seikosha , @yogiboy , For clarity on my original post, I used the word bias when referring to the 12AU7 and 12AT7 tubes on my newly acquired Quicksilver M120 amps when the term balanced should have been used. 
a_shah's avatar
a_shah
36 posts
 
@tooblue Did you figure out if you need to balance the 12AU7 on the QS-120 ?
I just purchased a pair of QS Mono 60 from QuickSilver ( not on the Website yet)
I was wondering if i could tube role the 12AU7 without balancing ?
A_shah
tooblue OP
787 posts
 
@A_shah, yes I was informed by the builder that the signal tubes do need to be ballanced. 
Log in to respond
More to discover
80x80
80x80
Peavey 3609520
Peavey IPR2 3000 Power Amplifier PEV03609520
80x80
Boulder 2108 Phono Preamplifier