Meaning of Bias Light on C-J amps ? ...

[joeinid]

Do I assume that when the red lights are "on" and glowing, the bias is "high"?

[Puma Cat]

Yes, it's just a bit high...take a thin-bladed screw driver and turn then so they just go out.

It's normal for them to come on and flicker during dynamic passages.

[joeinid]

I figured that. One tube was acting differently than the rest as far as bias went, so I had some spare EL34's, popped them in, and she's cooking now. I did a few preliminary bias adjustments and all seems well. I really like it. A lot

[Puma Cat]

Originally Posted by joeinid

I figured that. One tube was acting differently than the rest as far as bias went, so I had some spare EL34's, popped them in, and she's cooking now. I did a few preliminary bias adjustments and all seems well. I really like it. A lot

Excellent!

[turntable]

This is the simplicity and genius of the cj bias scheme.

You bias each tube individually as Stephen detailed, so no need to matched pairs, quartets etc.

If a tube fails, one it will not blow the resistors - at worse the faulty tube bia light will go red and the amp will switch itself off. If iot is a large failure, the large fuse at the back of the amp will also blow and show a red light indicating it.

It could not be easier

[joeinid]

I was going to just replace just the tube that was giving a problem but I had 4 of the same vintage. It actually biased much easier than what was in there so I am glad I replaced all of them. I'll have to think about replacements for the future.

[ronenash]

Just make sure you bias the amp when it is fully warmed up. After 30 minutes to an hour. New tubes will require rebiasing every couple of days until about 50-100 hours and then they will keep steady bias until you have sucked all the life out of them (~3000 hours).
Enjoy your new CJ. Its up there with the best.

[joeinid]

Thanks ronenash!

I'm pretty comfortable with checking bias, except I've always used meters. The amp is a sweet little thing, I like it very much. I guess the smaller input tubes can get changed every 2-3 output tube change, or should everything be changed at the same time?

Joe

[ronenash]

Originally Posted by joeinid

Thanks ronenash!

I'm pretty comfortable with checking bias, except I've always used meters. The amp is a sweet little thing, I like it very much. I guess the smaller input tubes can get changed every 2-3 output tube change, or should everything be changed at the same time?

Joe

Hi Joe,
I usually replace them all together because I never remember to keep track of what was replaced and when. In addition the price of the inputs in relatively low. You can get replacement tubes from CJ at a bit above the market price for those tubes and buying from CJ has the advantage of each tube being tested and matched. The downside is you have to purchase a full set.

Enjoy!