Biasing Carvin V3M

[flanstar667]

I'm having some issues biasing my Carvin V3M, and I was wondering if anybody could help me troubleshoot:

The tl;dr of biasing a Carvin amp is that you hook up a multimeter across the standby switch and read the mA while you adjust a bias control pot on the board.

I've got my meter hooked up to the switch, have the amp on and in standby, speaker plugged in, amp at 50w, and all volumes at 0.

The reading I'm supposed to be getting is ~80mA, but the reading I'm actually getting is ~40mA. Stranger still, when I adjust the bias pot, I see no change in this reading.

I tried putting the original set of tubes back in and got the same reading, so I don't think the problem is bad tubes. I've also confirmed that the meter gives good readings with a AA and 9v battery. The only thing I can think of is that I must be missing some step or instructions somewhere that I can't see.

Does anybody have any suggestions for things to try?


Footnote: Here are Carvin's detailed instructions for biasing this amp, which I've been following: http://www.carvinservice.com/crg/faq...m_and_v3mc.pdf

I can also get pictures if it would help.

[Enzo]

Other than the bias thing, does the amp work and sound OK? If so, at least we know the amp works.

How did you check your meter with a 9V and AA batteries? The test procedure requires you to read CURRENT, so if you check the meter by measuring the 9V at the battery that is not current, that is voltage. Meters have small fuses in the current section, yours could be blown.


On the other hand, with this connected across the standby switch, does the amp still function - make sound?

[flanstar667]

Hey Enzo, thanks for the quick reply.

You are correct that I checked the meter with voltage, not current. I made the assumption that if it measured voltage correctly, then it would also measure current correctly. If this is not a correct assumption, then the meter could in fact be the issue.

On the positive side, I plugged into the amp with the meter on it and it sounded fine (quite nice actually). All three channels had proper volume, and there is no crackling/popping/buzzing.

[g1]

The meter is the issue. You can only bias with that method if you have the meter set to current and the probes in the appropriate jacks on the meter. The amp is switched into standby mode and the meter acts as a short, like the standby switch would be if set to "run" mode.