#1
After i ordered my new tubes form Eurotubes, I checked out their video for biasing Marshall DSL/TSL's and found it to be really simple using my dad's multimeter.

I did as the guy said and had the right 2 tubes and the left 2 tubes both at about 88-90 mV

well, since then, i have probably RE-biased my amp 4-5 times because the numbers never seem to stay in place. it'll go from 88/88 on both sides to like 77/124

the video instructions said soemthing like do a bias with your guitar plugged in, play to find the sound of your liking, then do a final bias.

i really dont understand why the numbers keep fluctuating so much

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#2
Did you let your amp heat up before biasing? That can make a difference.

EDIT: I'll just rephrase myself, did you remember to let your amp tubes heat up properly for at least 10-20 minutes before biasing? I have heard that it makes quite a difference as the bias changes with the temperature.
Last edited by anubiz03 at Jul 30, 2009,
#3
Quote by anubiz03
Did you let your amp heat up before biasing? That can make a difference.

EDIT: I'll just rephrase myself, did you remember to let your amp tubes heat up properly for at least 10-20 minutes before biasing? I have heard that it makes quite a difference as the bias changes with the temperature.


that makes perfect sense, but i've actually jammed on my guitar for like 30-45 minutes a few times before biasing, and I'm sure it was hot enough then. hopefully though, it's what you said

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#4
One of the tube amp books I have says checking/setting bias should be a regular maintenance thing not just when you swap tubes. Tubes change as they age so the bias drifts.
#5
^

that also makes sense Tackle, but almost EVERY time i play?! that shouldn';t be the case.

What you're syaing is almost like changing strings, it should be a regular thing to do, but not EVERY time you play your guitar

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#6
damn, this is an interesting thread. i just wish i could give you an answer, but i would be very interested in the answer
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#7
Quote by gumbilicious
damn, this is an interesting thread. i just wish i could give you an answer, but i would be very interested in the answer


XD... this actually does feel like the first "scholarly" thread I've created since I joined haha. I really would like to know why they keep fluctuating, i mean the guy in the video told nothing about them changing frequently, or what steps you needed to do after biasing

so confused

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#8
How long has it been since you biased them initially?
The bias will definitely drift for the first few weeks of use, so if you're rebiasing every day then you're just fighting the inevitable.
If that's the case, just play the amp for two weeks as-is and then rebias it, and leave it alone.
#9
Quote by Roc8995
How long has it been since you biased them initially?
The bias will definitely drift for the first few weeks of use, so if you're rebiasing every day then you're just fighting the inevitable.
If that's the case, just play the amp for two weeks as-is and then rebias it, and leave it alone.


hmmm...interesting. I biased them initially around, eh... June 18 or 19th.

but then i didnt play for a while. I jammed with a friend the first week of July, then i didnt play much until yesterday just because my cab was in my car and i was too lazy to take it out and bring it up to my room

but ya...that's about when.

so you're saying just bias it...play reguarly for like 2 weeks or so, then re-bias?

that shouldn't be a problem, it's just when the numbers are off, i have a hard time bearing the tone of the amp cause it sucks hard lol

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#10
Sounds like that's your problem. The tubes need to be 'burned in' and the bias will be all over the place until they are, which is what you've inadvertently discovered by rebiasing them so often.

The good news is that you have an excuse to play loudly ever day for a couple weeks, and after that you can rebias and then not have to worry about it for a while.
#11
DSL and TSL bias is not the best setup IMO, I see the reasoning behind it though, with the way they have it setup now you could actually have two pairs of instead of a matched quad.
A single bias sweep like thats is on the JCM800 and most other adjustable bias amps is much simpler and easier to use. I sugest playing hard for a week then rebias, if the setting change again give old Bob at eurotubes a call mabe he can shed some light the problem. To me it almost sounds like an amp or a tube issue, really once the bias is set properly it should not really move to much after your tubes are properly broken in, its kinda wierd that your amp bias rate seems to be floating around.
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Last edited by Johnbryant at Jul 30, 2009,
#12
Quote by Johnbryant
DSL and TSL bias is not the best setup IMO, I see the reasoning behind it though, with the way they have it setup now you could actually have two pairs of instead of a matched quad.
A single bias sweep like thats is on the JCM800 and most other adjustable bias amps is much simpler and easier to use. I sugest playing hard for a week then rebias, if the setting change again give old Bob at eurotubes a call mabe he can shed some light the problem. To me it almost sounds like an amp or a tube issue, really once the bias is set properly it should not really move to much after your tubes are properly broken in, its kinda wierd that your amp bias rate seems to be floating around.


well i havent really played THAT much on the new tubes since i installed them, so that may be the problem; that the tubes haven't "broken in" enough yet to get a steady, stable reading.

so ill try what Roc said

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#13
i should have figured the 'roc' would drop on the scene and set things straight. i am definitely filing this tidbit away
punk isn't dead, it's always smelled that way.

"A perfection of means, and confusion of aims, seems to be our main problem."
-ae
#14
Regular maintenance does not imply every time you play. That would be tedious indeed and expensive if you paid for biasing like many do. Most will get new tubes maybe get their amp biased and thats the last time its touched until the tubes burn out again. But a person might get more life out of their tubes if they checked the bias on occasion might even give you a clue as to when they were getting close to needing replacement.

Old air cooled bugs with new valves you checked the valve lash after 20 minutes of run time then at 25 miles then at 300 miles. The break in period. They shifted most during this time. And you checked em at every service if kept adjusted they would go alot longer before problems. If you ignored em and let em get loose or tight then you had expensive problems.

Let your tubes drift to hot and it can make big problems, blown fuses, fried resisters, burned circuit boards etc when they do finally go out. Drift cold your tone suffers. Or in TS case 1 hot 1 cold. Then you have 1 tube doing more work than the other which will make it burn out faster.