Biasing, but at what price? - Jemsite
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post #1 of 8 (permalink) Old 04-23-2003, 09:31 AM Thread Starter
 
Join Date: Dec 2000
Location: Discoville, IF
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Biasing, but at what price?

Howdy everyone.

What seems to be the usual fee for biasing a tube amp?
The net doesn't provide too much info, although I've seen figures like $25.

The techs 'round here seem to charge exorbitant fees for tubes and biasing, and I'm this [] close to getting the know-how together and starting to do it myself. As a fan of tube amps, I guess I'd be biasing lots of amps in my life if I don't happen to kill myself with them. Ah well.

Any input is welcome, as usual.
Mr Orange is offline  
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post #2 of 8 (permalink) Old 04-23-2003, 12:09 PM
 
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A biasing tube amp?? What's that??
little wing is offline  
post #3 of 8 (permalink) Old 04-23-2003, 01:22 PM Thread Starter
 
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It's setting the optimum plate current for the power amp tubes in your amp...
Too little (running the tubes "too cold") results in crossover distortion & leave the amp sounding sluggish and lacking dynamic response, and too much ("too hot") results in very short tube life. Both situations are undesirable. Biasing must be done because basically every set of tubes is slightly different.

Bias must be set in any amp using EL34, 6L6, 6550, KT88 etc tubes in the power stage. Preamp tubes are self-biasing. If you replace power amp tubes with same brand & valued tubes, no biasing should be necessary.

EL84 power amps usually run in class A and have fixed bias, so biasing is not required when changing tubes. Although some say that Mesa amps which claim to be fixed bias, are set to run a bit too cold, and major tone improvements can be made by adjusting the bias to slightly hotter.

And then there're the THD univalve, GT Single and some other amps that are self-biasing.

I hope that answered your question in some way.
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post #4 of 8 (permalink) Old 04-23-2003, 02:19 PM
 
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There are several amp book out there, like "How to Service Your Own Tube Amp", and "Inside Tube Amps", and a new one by Gerald Weber, although I don't know if I'd be comfortable with his writing style if it is anything like his self promoting. Sometimes he comes off as too smart for regular folk, and that may make for a difficult read when your amp guts are hanging out of the chassis. But I haven't seen his book so it might be awesome. The price of the books are all around $30, same or less than a bias job, and you should get a lot of other good info. I knew how to do it once, a long time ago, but I always had amp guys around me who did it for free and I just plain forgot. I've had my main tube head for over 15 years and it was biased for the tubes that are in it about 5 years ago, so I'm sure someday it will come up. I just record with it now so the power tubes will last quite awhile. Incidentally, if you do get a book, maybe you can give us a review.
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post #5 of 8 (permalink) Old 04-23-2003, 02:44 PM
 
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From what I've seen, you can expect to pay around $25-$50.00 depending on the amp and the amount of work entailed in getting it dialed in.

My old shop charged $60.00/ Hr. and I got 1/2, so...

You'll really have to do some research around your area and see who can do the job for the best price, just make sure they are actually servicing it and not sending it out. you'll save time and money by going directly to the source.

Bamm
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post #6 of 8 (permalink) Old 04-23-2003, 05:24 PM
 
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I just called and asked the same thing for my early 60's danelectro amp. I was quoted $30, which seems reasonable for a 40 year old amp.

Todd
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post #7 of 8 (permalink) Old 04-23-2003, 09:47 PM
 
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and most important of all listen to the amp while you bias, your ear is the most important factor, no matter what any manufacturer says whan you change the power tubes is a good thing to check out the bias, since any tube is basically hand made avery one has is particularity, maybe minimal but there are.
Stefano
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post #8 of 8 (permalink) Old 04-24-2003, 02:47 AM
 
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Wow.. thanks for the information guys. Didn't know anything about it actually... My amps were never biased tough..
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mesa amps , power amp , power amps , preamp tube , tube amp , tube amps , tube head

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