View Full Version : Yaqin MC10L biasing and other problems

01-04-2013, 08:35 AM
I've used it with stock tubes. Recently I noticed some distorted sound, and I tried to change them with Siemens EL34 tubes. Evidently one of the tubes were at fault, and the fuse got blown up.
Then, I used a spare fuse (not fast blow fuse, but slow blow fuse) and put back the original tubes, and tried to set the bias.
On my voltmeter, I can set one tube to 0.35V, but all three other tubes showed 8 Volts and up at minimum setting. The color of the tubes were very bright, so I quickly powered off.
When the fuse got blown up, I also sensed some burning smell. One of the resisters might have been damaged.

So, anybody can tell me what can I do to successfully bias my Yaqin? Previously, I did not have a problem of biasing all tubes at 0.4V.
Since the new purchase, it has blown up a fuse and resistor two times -- first time, about a month after I changed to Siemens tube. At the time, I did not bother to bias the tubes. Second time, when I moved to a new place. Again, I did not bias the tubes after the move.
Lessons that I had learned: always bias the tubes when they are replaced and when you move to different places where the voltage signal may be different.

Any comments would be appreciated.

01-04-2013, 09:33 AM
Did you use the spare fuse that is in the tiny slide out tray that is right next to where the power cord plugs into the amp? That is the only fuse that should be used.

The amp will need to be repaired.

Sorry to hear that you learned the lesson too late about the importance of rebiasing after tube rolling.

01-07-2013, 01:05 PM
use the same type fuse that came with it.. bias in .35 Ma
i got one thats running good 5 yrs this April..