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Post by edoetsch on Jun 26, 2007 12:32:57 GMT -7
I have looked at www.eurotubes.com/euro-Generic-Bias.htmand gotten some great advice from user iggs about the location of the bias trim pot (having never opened up the amp yet) I have a Radio Shack Volt meter which I mostly use to test batteries and bypass loops I create and guitar rewirings I've tried. So I am probably about a 5 out of 10 in electronics. Is my meter going to be good enough? Do I just need to get the amp (in mA) from pin 3 on the tubesocket to the chasis? (One handed to keep the ol' heart safe) Should I spend $100+ to keep myself extra safe?
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Post by iggs on Jun 26, 2007 13:14:33 GMT -7
You're welcome! ;D
Unless you're an amp tech or very, very comfortable with poking around electronics with DC voltages at 450V, I'd say Weber BR is the way to go. For me, it was a great investment not because I'm too cheap to pay a good tech to bias my amp but because I was able to quickly change tubes and experiment without having to run out to a shop every time. If you plan on doing the same, the Weber BR will pay itself off quickly. If you are going to put a new set of tubes in and leave them be for next few years without ever checking the bias or experimenting with different tubes, then I'd say save your money and have a tech do it.
Some folks will argue the accuracy of the Weber BR but for me, I'd say it's pretty darn close.
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Post by nitehawk55 on Jun 26, 2007 15:45:08 GMT -7
If only the bias pots were accessable without pulling the chassis that would be a great feature
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SG123
Full Member
Posts: 221
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Post by SG123 on Jun 26, 2007 17:56:48 GMT -7
"Do I just need to get the amp (in mA) from pin 3 on the tubesocket to the chasis? "Pin 3 on your output tubes is the plate - high DC voltage there, and NOT where you want to measure bias current. I suggest getting some type of bias "tool"/measurement device. You really don't need to pay extra for one with a meter since you already have a meter with a mA. scale. I like amps with an externally accessible bias pot, but I can understand why a manufacturer would want to limit access to them. What I don't understand is someone building a fixed bias amp with NO adjustment at all - unless you unsolder and change a fixed resistor.
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Post by woody on Jun 26, 2007 19:53:41 GMT -7
If only the bias pots were accessable without pulling the chassis that would be a great feature In addition to that how about a built in digital readout to tell you what the measurement is...is that possible?...i know nothing about electronics.
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Post by zdogma on Jun 26, 2007 19:55:54 GMT -7
I like my biasrite a lot. I asked myself the same question, and $100 isn't a lot to pay for the added mesure of safety.
I completely agree agree with nitehawk about the external pots. Its a pain in the butt to bias my Z 28.
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Post by hdahs143 on Jun 26, 2007 20:58:29 GMT -7
If there is any doubt at all about bias procedures and how to safely perform them, the Bias Rite is a great investment. For the difference in cash between the stripped model with the V1 switch ($60), and the complete BR-2 model ($110), I'd go for the complete model. It has 2 sockets, a built in meter, and the V1 switch which displays plate volts, which you need to know to set the bias correctly.
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Post by iggs on Jun 27, 2007 6:34:04 GMT -7
You might already know this but I think it's worth mentioning how to calculate the desired bias current:
Most people will say that you should bias the amp to not more then 70% of max plate dissipation.
KT66, max plate dissipation is 25W.
25Wx0.7=17.5W
Plate voltage will vary in any amp depending on what's coming out of the wall, which is why Weber BR is also useful since it gives you the plate voltage in addition to the current. Ideally Route 66 will put 450V on the plate.
Knowing that, we can calculate what is the highest you *should* bias your amp to.
17.5W/450V=0.038A or 38mA
If you take 50% of max plate dissipation as your lowest point you get:
25Wx0.5=12.5W
12.5W/450V=0.027A or 27mA (IMHO that's way too cold, but you get the point)
For me, anything between 33mA - 37mA at 450V sounds good with Route 66, and it's within the safe operating range.
It gets a bit tricky when your plate voltage starts varying depending on your wall voltage (unless you have a hefty voltage regulator) but using the same math you can judge and guess how the current will fluctuate with the varying voltage and then bias accordingly.
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Post by hdahs143 on Jun 27, 2007 7:33:16 GMT -7
It's also important to remember, that as the bias current increases, plate voltage decreases, and consequently affects the bias calculation.
Weber has a bias calculator on his site that includes some tables for the various tube types, that show bias current at various dissipation percentages, and plate voltages.
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Post by edoetsch on Jun 27, 2007 13:21:55 GMT -7
I look at all of this information in 2 ways.
1) It is fascinating, because I love tech information. I am a computer engineer and even took an electronics course 15 years ago. It makes me want to under the hood an tweek around and learn even more. However, if anyone read my post in the Pedals Section, we are dealing with some of the top amps in the world and a tweek here and there is so minimal compared to owning a crap amp, why even bother.
2) I am a guitar play who owned a Peavey Classic 50 for 10 years before even opening the tube section of the amp. I used to just play guitar and not worry about what I was playing through, just the chords, man.
Anyway, thank you for the info. I will probably continue to TWEAK!!!!
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Post by myles on Jul 6, 2007 16:55:45 GMT -7
A simple answer to the question in the title of this post is:
Yes
It will pay for itself in no time at all and if you bias the amps of others (at $25 a crack) they will get the job done right and at about 1/2 the going rate and you will make some lunch money.
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