[7 Dying Trees]

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?

[loktide]

Eurotubes

answers you shall here find

[eleven59]

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

[JJ Rodriguez]

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

[7 Dying Trees]

Originally Posted by loktide

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.

:/

[7 Dying Trees]

Originally Posted by eleven59

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

[7 Dying Trees]

Originally Posted by JJ Rodriguez

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

Very true

[Austin]

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

[7 Dying Trees]

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...)

[ChrisPcritter]

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..