Bias

kirk · #1 08-28-2002, 05:40 AM

OK, probably need to retube my head. So, if I use identical tubes (maybe a different manufacturer) do I have to do this bias thing or what?

If so, is this something that someone as inexperienced as me can do, or should I have a pro do it?

jeff l · #2 08-28-2002, 08:21 AM

What amp are you talking about? If it's a class A type of an amp then the tube (like an EL-84) determines the bias but most amps require a re-bias when you replace the power tubes. Otherwise you amp may perform poorly and you'll eat up your tubes much faster.

Do *not* f##k around. Take it to a tech as a re-bias involves adjustments while the amp is running. It's definitely not for the novice!

kirk · #3 08-28-2002, 01:21 PM

Quote:

Originally Posted by jeff l

Do *not* f##k around. Take it to a tech as a re-bias involves adjustments while the amp is running. It's definitely not for the novice!

Jigowatts. I know that there's an awful lot of power coursing through the thing.

The Pre Amp tubes are ECC83's and the Power Amp Tubes are EL34.

I have another question, what would you recommend using when replacing the tubes? (brand)

I am going to call around. Maybe somone will let me watch them do it a few hundred times. And I thought intonation was difficult......

Thanks for the tip.

jeff l · #4 08-28-2002, 01:43 PM

Hey Kirk....sure no problem dude. Uhm, as far as EL-34's go I like Svetlanas but some people also seem to like the JJ brand. From what I can gather, I hear the JJ's have a bit more bottom end punch to them and the Svets (which I have in my Marshall) are nice and smooth. Ask your tech about both brands.

Regarding the biasing, you also need the proper equipment to gauge the plate voltage. Add to that some techs use the bias meter to get in the ballpark and then tweak from there. I'm all with ya on the saving money part but this is one job best left to a good tech with lots of experience, imho.

kirk · #5 08-28-2002, 02:12 PM

So, if I was to replace the tubes, I definitely need to have the bias done also, or can I just swap out the tubes?

BTW this is a Laney AOR head.

jeff l · #6 08-28-2002, 02:23 PM

You need to have the amp re-biased if you're changing the power tubes (even if they're the same type and brand) in that amp. You'll be taking a risk of possible damage and /or a performance hit if you don't re-bias.

The whole reason for it is because power tubes of identical type and manufacturer will run at different optimal plate voltages. It's just the nature of the beast. That's why you buy these things in matched sets.

Oh yeah, your tech is also probably going to want to replace the driver tube (the ECC83 that is located closest to the power tubes.)

kirk · #7 09-10-2002, 01:42 AM

Went with the Svetlanas and Tesla JJ 12ax7. Having it biased on Wednesday.

BTW Jeff, I am bringing the amp over to Canada on Wednesday afternoon when the tubes arrive. The guy is only charging me a $25CAD bench fee.

Additionally, he is working on some pretty cool sounding hand made amps. He's got a website, but there is not much info on it yet: Dynamic Sound Research Supposedly he just built one for Jeff Healey.