# What Bias Probe to get?



## 7 Dying Trees (Jan 18, 2008)

All you guys that bias your own amps, I've decided to go experimental and use my incoming cheap 5150 as a testbed for learning to do this  I'm well aware of the danger, but, in all honesty, it shouldn't be too hard and it's something I've decided I am going to learn how to do. (At the same time I may as well properly learn about tube amps this way as well, see if I can put to use the 4 years odf electrical engineering i did)

So:

What bias tool do i need? 

Where do I get it from?

Any gotcha's to do with multimeters and ratings I should be aware of?


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## loktide (Jan 18, 2008)

Eurotubes

answers you shall here find


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## eleven59 (Jan 18, 2008)

Well, for starters, does the 5150 you're getting have adjustable bias?


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## JJ Rodriguez (Jan 18, 2008)

The mod is simple enough if it doesn't already have it.


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## 7 Dying Trees (Jan 18, 2008)

loktide said:


> Eurotubes
> 
> answers you shall here find


I have looked, but there's several, and although there's a lot of answers, all I want to know iss whether the 25$ probe is enough, or whether i need two of them. 

:/


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## 7 Dying Trees (Jan 18, 2008)

eleven59 said:


> Well, for starters, does the 5150 you're getting have adjustable bias?


No. But I have the bias mod schematics, and I'll be doing that one myself once i get the parts  THe 5150 is going to become a little test amp for mods for a while to see what I can do to it


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## 7 Dying Trees (Jan 18, 2008)

JJ Rodriguez said:


> The mod is simple enough if it doesn't already have it.


Very true


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## Austin (Jan 18, 2008)

I have the Weber Bias Rite (BR 2? I'm at work...) and it works fine. If you purchase that model, you may want to buy a right angle adapter as well if you don't want to remove the amp from the chassis. I have one adapter for the 5150, one for the Triple Rec (the sockets are set differently so the angle of the adapter has to account for the direction of the tube socket keyway). 

Weber Bias Rite cathode current monitor


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## 7 Dying Trees (Jan 18, 2008)

Hmmm, well, i just ordered their stard ones as I have a multimeter already, and I am going to have to take the 5150 out of the chassis anyway as I am going to do the bias mod to it (fairly simple). 

Also ordered a 5150 retube kit off them at the same time, which worked out cheaper than buying the tubes here, sadly enough :/
(well, not sad for me, even with import it's still cheaper...)


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## ChrisPcritter (Jan 19, 2008)

That should work fine. The plate voltage of the 5150 is 480. 

The 5150's are set at around 12ma with stock tubes. They don't start to sound really good til they go over 20ma. I like the sound best at about 30ma. According to BOB at eurotubes this is how you figure out what's safe. 

25 watts divided by 480 is 52ma Which is 100 perccent idle current and will fry your tubes, but you have to figure out 100 percent to get the specs

65 percent is a good starting point adn is 33.8ma

The max of 85 pecent is 44.2ma and will cause your tubes to burn out faster.. 

I also have a couple pics of how to make the clean channel footswitch controlled if you want them.. They are hard to see..


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## heffergm (Jan 19, 2008)

ChrisPcritter said:


> That should work fine. The plate voltage of the 5150 is 480.
> 
> The 5150's are set at around 12ma with stock tubes. They don't start to sound really good til they go over 20ma. I like the sound best at about 30ma. According to BOB at eurotubes this is how you figure out what's safe.
> 
> ...



You can even get away without doing the calcs, because Bob @eurotubes has been kind enough to post a lot of this info on his generic bias video page. For the 5150:

Peavey 5150 (with bias mod), 5150 II, XXX and JSX. 480pv - 36 to 42mA

Voila. All you need is a $20 multimeter and the $25 eurotubes bias probe, do the bias mod, and set the bias between 36 and 42mA. Took me all of 10 minutes on my JSX.


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## kmanick (Jan 19, 2008)

heffergm said:


> You can even get away without doing the calcs, because Bob @eurotubes has been kind enough to post a lot of this info on his generic bias video page. For the 5150:
> 
> Peavey 5150 (with bias mod), 5150 II, XXX and JSX. 480pv - 36 to 42mA
> 
> Voila. All you need is a $20 multimeter and the $25 eurotubes bias probe, do the bias mod, and set the bias between 36 and 42mA. Took me all of 10 minutes on my JSX.


 
Exactly, same here, setting the JSX is a piece of cake.


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