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In Reply to: Re: biasing CJ MV60; sound effects posted by steven oda on September 22, 2002 at 22:45:15:
Thanks for the reply, Steven.I have a question or two to ask. I have no serious ideas about tube amps so my questions will reflect that, as you, no doubt, could tell from my previous post.
First, if the the amp is "over-biased," what, exactly, should I do. With the CJ MV60, the bias is within the normal range, so says the manual, when the small light is lit. The manual suggests that I turn the bias screw counter clockwise until the light goes out (or clockwise to get it to turn on), then back, ever so slightly, until it turns on. That, presumably, puts it within the normal range.
I assume you are suggesting I experiment with "under-biasing." If I understand the implications of that suggestion for my amp, I should either turn the screw clockwise until it turns off in that direction and then leave it close to the on-off point, either with the light on or off. Does that sound right?
Second, I'm not certain what the term "idle bias" means. I assume it means, as the manual suggests, that when I check the bias all components are turned on but I'm not playing anything. Thus, the amp is "idling." Again, does that sound right?
Thanks, again, for the advice.
John
Follow Ups:
The MV60 manual I have says the bias is set properly when the light goes off, not on. It says you may have to turn the bias clockwise slightly to cause the light to go on, but then to turn it counterclockwise until the light is off. This is in sync with what my dealer advised on biasing. This procedure should be performed with no music signal activity, but all equipment should be online.Lynn
Lynn,I agree with you about the manual. But I'm still in a quandry. If I should overbias or underbias, how should the bias settings be left?
Here's what I assume. Please tell me if I'm right or just horribly wrong.
To overbias would be to turn the bias screw counter clockwise until the light goes out, then take it a bit further. To underbias would be to leave the light on.
I've done a first run at resetting the bias and it hasn't helped the sound.
And another question. Do you have any idea if the sound is affected as tubes degenerate? If so, how?
I would appreciate any help you can offer.
John Kendrick
Hi,I am not sure, but I would think that the red light indicates an overpower condition. So, if one wanted to over bias leaving the light on would indicate that condition.
I am fairly new to tubes, but it is my understanding that as tubes degrade the sound is affected. Depending upon heat, the type of tubes, how often you power on/off the life of the stock tubes is supposed to be between 1500-2000 hours depending upon your tolerance to sound quality.
Both my dealer and CJ have said that when tubes degrade the first thing to go is the bass and sound dynamics. The best way to check is to get some new tubes and swap them and see the difference. That said, different brands of tubes sound different new so the only valid check is with the stock tubes.
I am trying various tubes now and have not decided what is best, but you can definately tune the sound of your system to your tastes by using different tubes. For now, I am focused on the 12AX7 tube. The stock tube is fairly warm in detailed, moving to a tube from a company called EI the sound is more detailed and dynamic, moving to a vintage tube from telefunken the sound if more warm and mellow. Depends upon what you want.
Personally, I would rather play with different types of tubes rather than over biasing the power tubes since it will shorten their life.
Regards,
Lynn
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