andyhatescrass

One more quick one 311, am i turning the vr1 or vr2 under the chassis, when measuring the bias?

311ZOSOVHJH

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311ZOSOVHJH

I sent you a PM with my cell phone number if you get stuck

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andyhatescrass

Everything went well the first time around. Yesterday, I set the bias around .31mA and played it right after and it sounded great. After about an hour of letting it sit, I played it again and it sounded different; I thought it would be too hot, but I just checked the bias was pretty cold, around 26mA. Is this what normal bias drift is like, or are the tubes possibly going bad? They've been played pretty heavy for 8 or so months and have not been biased until now.

fly135

I'm not an amp tech but it sounds like the bias drops as the amp heats up which suggests you should set the bias to the high side if adjusting it while cold. Or adjust it after it's hot.

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andyhatescrass

One thing ive noticed that i forgot to mention: When letting the bias settle with the multimeter plugged in, it doesnt really settle. Just climbs slowly. I set it just below .31 and in 5 minutes, it was at 32.5 and still climbing. That was why i was thinking the tubes might be bad.

EDIT:
Just saw your answer above mine, Fly. So I suppose it would make sense for me just to let it settle as high as it can, which would signify that it is running hot, correct?

311ZOSOVHJH

Yes you need to let it sit. Yes bias drift is normal. Don't play the guitar through the amp with the probe plugged in. Don't bias to numbers, bias to how it sounds. How are things going at this time? Tubes don't hold the bias, the amp does. Not sure if 'bad' tubes would cause the amp to drift. Question is does the bias finally settle in on a number.

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trashedlostfdup

may be irrevelant, but if you are going to do much with amps beyond biasing i would get a better DVOM. i use snapon, by far the best meter i have used. isn't cheap, but its worth it IMO.

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R45VT

No offense Snap-On brands suck. Most are BluePoint. Slow refresh times.

Best is Fluke for meters. Last meter you will ever buy. You can catch most glitches without a DSO depending on the signal. Snap-On you would miss it completely.

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trashedlostfdup

don't buy a blue point. i have wired up several drag car from scratch harness as far as wiring goes and used it for two amp builds and repaired several effects. its not as good for DSO, but they are worth the money. i got it at 50% retail as i went to trade school for six weeks. all i wanted to learn there is flow benching cylinder heads and a refresh on engine assembly, as well as dyno.

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R45VT

What meter do you have? I have not seen a Snap-On one that is not BluePoint.

I hate them. I hate most non-fluke.

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trashedlostfdup

its 7 or eight years old before much was blue point. all the new ones are bluepoint. they are really durable. i have dropped it in my concrete garage hundreds of times and have no problems.

i am pretty sure it is this model:

http://buy1.snapon.com/catalog/item...ore&dir=catalog

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R45VT

Meh. Better than BluePioint. I haven't seen one in recent time. I doubt the crap on dealer would even have them in stock. I'd have to use one in person to see how fast and accurate it is. I get sick of crappy meters. Too many techs have low budget ones that are lucky to have functioning leads.

I would still rather have a Fluke.

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Arby911

I've got to go with you on this one. There are 2 brands of meters, Fluke....and everything else...





Slow learner?

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andyhatescrass

Sorry for the late response, its been a busy week. I ended up getting the bias to settle earlier this week and it sounds like its in the right spot now to my ears anyway, it doesn't sound cold like it did. I played it for an hour or so after removing the bias probe, which may have been the key for getting it to settle.