Bias determines the operating point of the tube without a signal applied i.e. just sitting there at idle. Some amps want the tubes to be just barely on. Some want them to be biased halfway on.
In most cases it is a simple procedure, some require a multimeter, some you turn a screw until an LED lights up (or just turns off), and many amps have automatic bias so you don't have to worry about it. Any reputable manufacturer should provide a manual with detailed instructions on how to bias their amp. If you are concerned you might want to start with an auto bias amp to see if tubes are your cup of tea.
Don't know enough about those you listed to comment. |
Go to this link and punch in primaluna.
http://www.upscaleaudio.com/
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When I was toying with the idea of moving over to the tube side, just the thought of biasing with a meter, turned me off completely to the idea of tubes. Getting down on the floor with a meter, checking, obsessing over my tubes? Forgeddabout it. So, I go for a self biasing integrated. Now, after being exposed to the beauties of tubes and becoming truly addicted to the tube sound and if I had the opportunity to purchase a tube amp (that required self biasing) to die for? I'd get down on the floor with my meter and bias away. warren:)
BTW, my SET seperates are self biasing, thank god. |
I've had nothing but tube amps for 20 years. I started with the Moscode 600.Several amps latter I moved to CJ. I had the 5's for 4 years and the 8's for about the same amount of time. Both of these have the trim pots for each tube and are a breeze.--So folks don't get the wrong impression, I never did the meter thing. I would just take my amps in to have this done for me. On my Jadis, I ended up waiting till I had 2 bad tubes;then just had all the tubes replaced.---No techie,here.-- |
Most manufacturers whose products require user biasing, make it very simple in their current models placing biasing pots/points in convenient locations. For the most part, gone are the days where you need to remove the bottom cover and tip the unit on its' side and on and on. However, some imported products are still a PITA.
Regarding the meter, IMO everybody should own a multi-meter tubes nothwithstanding. One of the best $30-$50 investments you'll ever spend on your system. |
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In the back of my mind when I purchased my tube amp, I too, dreaded having to bias my VTL ST-150. But I wanted tubes and like anything else, I knew I'd eventually learn how to.
I had the bias instructions and I bought a decent multimeter at Radio Shack. When it came time to replace the tubes, I called the dealer, CSA in Montclair, NJ. I explained my inexperience and the dealer offered to bias the amp and show me how easy it is.
He was right. I took notes, paid attention and since then I've performed the operation myself. Go ahead, don't let the unknown keep you from experiencing "all" aspects of this hobby. |
Fyi, Decware makes terrific tube amps and preamps, and they are all self-biasing. Check out Decware.com .
Good luck |
Find out ahead of time how to bias the particular amp you're looking at buying - they are all different.
Some auto bias, so it's a total non issue for the owner.
I have a Rogue Zeus, which has a LOT of tubes. Rogue puts a meter right on top, built in. You just flick a switch for the tube you want to check, and adjust. It's that easy. Rogue might do this on all of their amps, I'm not a dealer - I don't know.
In my mind there are some advantages of being able to check bias - you should let the tubes warm up for a while before checking - auto bias checks them at the power up cycle. Also, you can check tubes periodically, and see if one changes faster than the others, and is on the way out.
I use my amp daily, and need to adjust them every 4 -6 weeks - but not by much. You feel like you are giving the thing a tune up - which I guess you are! |
Biasing is NOT difficult. Own a JoLida 502B. |
I don't understand auto biasing vs manual biasing? Why wouldn't all tubes be auto/self biasing? What is it about the nature of an amp, or the manufacturer, or whatever, that one would produce an amp without this feature? thanks in advance, warren :) |
Warren,
My amp designer states that auto-biasing impacts the sound of an amp, and not positively. Nick makes the best sounding electronics I've been privileged to hear, regardless of price, so I believe him. In top level gear manual biasing is probably preferable.
Aside from any degradation caused by unneeded complexities in the circuit, our own ears tend to confirm this from another direction. We readily hear any small changes we make in bias levels, so if the amp were constantly monitoring and adjusting...
Biasing and balancing four power tubes once every 6-8 weeks takes all of 10 minutes. It's no big deal, as others have said. YMMV of course.
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Well made amps don't require biasing very often, and it's a good idea not to go crazy with this simply because frequent biasing will prematurely wear out the pots.
The CJ and Rogue amps I have are basically set it and forget it. I check the bias once every six months or so on the Cronus but with the CJ I haven't had to touch the bias for almost year now. And I am running Winged C Svetlana EL34s in each. |
Stevecham,
Now that you mention it, I haven't actually *changed* the bias on my amp since I nudged a new quad of Sovtek Reflektors up to full operating level. That was last May or June, and they're running at the same level today and presumably for the forseeable...
I check it out of habit every month or two but, as you say, a well-designed circuit that doesn't overdrive the tubes should remain stable for long periods.
Great. Another thing NOT to worry about. I hate that!
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The Rogue M-150's I'm using hold bias very well. As others have mentioned biasing is really easy and not something that needs to be done very often. As I understand it, having a way to bias the tubes in the system can save you money in not necessarily needing to purchase well matched sets. I also like the option of running some tubes a bit warmer or cooler to tweak the sound. |
