Re-Bias at Home?

bgwatts · December 16th, 2004, 11:18 PM

I'm kind of getting the bug to get deeper inside my deluxe.I do most all ny regular repairs and mods.I.E. speakers ,pickups etc.
How much of a leap would it be for me to start playing with different brands of tubes?I've got a silverface DeLuxe.I understand that I can't just "plug and play".I quite sure I'm capable of learning the procedure,but what about equipment? Can I do it with care and basic stuff or would I have to get a "real" bech set up with something crazy like an 'scope?

Lance · December 17th, 2004, 07:39 AM

http://www.webervst.com/bias.html

I'd pick up a bias gizmo from Ted Weber - it comes with a meter. You get just get a single head unit to save cost. Essentially, this device allows you to read the device w/o pulling the chassis and subjecting yourself to the hazards with. He used to sell just the head without the meter part and you'd just plug the leads into a multimeter (Radio Shack $15) and take a reading. Either way, it's a great little gizmo at a fair price.

It's simple to do. Do a search in the forum on "bias" and "weber" and you'll see more info.

Daddy Elmis · December 17th, 2004, 09:54 AM

This assumes that the Deluxe has an adjustable bias pot (I don't recall right now whether or not it does). If so, basic biasing with Ted's device is pretty simple.

If not, you'd need to solder in new resistor at the necessary ohms to affect the bias (this is the case with my Bassman, and why I haven't gotten into doing my own biasing -- the other amps are EL84 based and don't really need biasing). That would be a pain, IMO, and not worth the hassle.

One of these days I have to install a bias pot in the Bassman

Ben Harmless · December 17th, 2004, 12:32 PM

Two things:

1. Something that Lance touched on: do not even open up your amp if you're not 100% sure you know what you're doing. Some of us have done it so many times that we forget to bring it up, but there are charges inside pretty much any tube amp that will kill you. Do not assume "might," think "will." You can drain these charges in several ways, this is my method, and it works like a charm.

2. I own and use the Weber Bias Rite, and it's a great tool. Keep in mind, however, that while it does measure the important things from the outside, it does not keep you from having to open up most amps to get to the bias pot. See point 1.

Once you're able to do these things youself, it really frees you from worrying about bringing your amp into the shop like everyone tells you to do. If you're good with an iron, you'll probably feel confident enough to start tinkering further soon. Congrats, and enjoy!

Wally · December 17th, 2004, 01:04 PM

Bg, that SFDDR has a bias adjustment that is accessible from the underside of the chassis. The chassis does not need to be pulled to adjust the bias pot. A bias rite or similar tool would be very handy and would tell you exactly what current draw you are achieving. However, with care, one can adjust the bias according to what the player wants to hear within the range of safe current draw. Using a small screwdriver, one can adjust the bias one way (clockwise is viewing the bias pot upside down) until the plates begin to turn red. Back off of this setting as the red plates indicate too much current draw and the tubes will not live long. Just before the plates go red is the maximum current draw at which those tubes will work and survive. Distortion will occur most quickly at this setting...the amp will be 'hot'. Some folks like this sound, but know that tube life is shortest at this setting. Going away from this setting one is decreasing the current draw. The sound will progressively get 'cooler' with more headroom. At some point, the current draw will decrease to the point where the sound becomes very cold and sterile..much like a solid state amp...and harsh crossover distortion will occur. Toward this end of the range, tubes will have extended life. Within this range, one can pick what works for them. Also within this range is the 70% dissipation point at which most techs will advise that the current draw be set for good sound and acceptable tube life. This method I have described is especially handy if you are caught needing to change tubes but have nothing but a screwdriver and your ears with which to do the job.

1612112 · December 17th, 2004, 01:15 PM

Ben is right you need to discharge those filter caps in the amp and his method is good. However be careful because current can reappear in those caps because they have a chemical memory. Go a step further and have an earthed lead attached to the chassis while you work and a jumper wire from the power side of those caps (they should be all on the same rail/supply) to the chassis. I've was burned for the last time a few years ago. A little knowledge is dangerous but don't let that put you off this is easy but you need to be respectful of the somewhat mysterious electrickery.

December 16th, 2004, 11:18 PM	#1 (permalink)
bgwatts Tele-Meister Join Date: Sep 2003 Posts: 226	Re-Bias at Home? I'm kind of getting the bug to get deeper inside my deluxe.I do most all ny regular repairs and mods.I.E. speakers ,pickups etc. How much of a leap would it be for me to start playing with different brands of tubes?I've got a silverface DeLuxe.I understand that I can't just "plug and play".I quite sure I'm capable of learning the procedure,but what about equipment? Can I do it with care and basic stuff or would I have to get a "real" bech set up with something crazy like an 'scope?

December 17th, 2004, 07:39 AM	#2 (permalink)
Lance Friend of Leo's Join Date: Mar 2003 Posts: 2,197	Easy to do! http://www.webervst.com/bias.html I'd pick up a bias gizmo from Ted Weber - it comes with a meter. You get just get a single head unit to save cost. Essentially, this device allows you to read the device w/o pulling the chassis and subjecting yourself to the hazards with. He used to sell just the head without the meter part and you'd just plug the leads into a multimeter (Radio Shack $15) and take a reading. Either way, it's a great little gizmo at a fair price. It's simple to do. Do a search in the forum on "bias" and "weber" and you'll see more info. __________________ Lance "not very good...but I make up for it by playing loud"

December 17th, 2004, 12:32 PM	#4 (permalink)
Ben Harmless Friend of Leo's Join Date: Mar 2003 Location: Albany, NY US of A Posts: 3,375 12 Photos	Two things: 1. Something that Lance touched on: do not even open up your amp if you're not 100% sure you know what you're doing. Some of us have done it so many times that we forget to bring it up, but there are charges inside pretty much any tube amp that will kill you. Do not assume "might," think "will." You can drain these charges in several ways, this is my method, and it works like a charm. 2. I own and use the Weber Bias Rite, and it's a great tool. Keep in mind, however, that while it does measure the important things from the outside, it does not keep you from having to open up most amps to get to the bias pot. See point 1. Once you're able to do these things youself, it really frees you from worrying about bringing your amp into the shop like everyone tells you to do. If you're good with an iron, you'll probably feel confident enough to start tinkering further soon. Congrats, and enjoy! __________________ "I think I'll go for the life of sin, followed by the last-minute, presto-change-o, deathbed repentance." - B. Simpson

December 17th, 2004, 01:15 PM	#6 (permalink)
1612112 Tele-Meister Join Date: Nov 2004 Posts: 229	Discharging caps... Ben is right you need to discharge those filter caps in the amp and his method is good. However be careful because current can reappear in those caps because they have a chemical memory. Go a step further and have an earthed lead attached to the chassis while you work and a jumper wire from the power side of those caps (they should be all on the same rail/supply) to the chassis. I've was burned for the last time a few years ago. A little knowledge is dangerous but don't let that put you off this is easy but you need to be respectful of the somewhat mysterious electrickery.

December 17th, 2004, 09:54 AM	#3 (permalink)
Daddy Elmis Tele-Holic Join Date: Jun 2004 Location: USA Posts: 961	This assumes that the Deluxe has an adjustable bias pot (I don't recall right now whether or not it does). If so, basic biasing with Ted's device is pretty simple. If not, you'd need to solder in new resistor at the necessary ohms to affect the bias (this is the case with my Bassman, and why I haven't gotten into doing my own biasing -- the other amps are EL84 based and don't really need biasing). That would be a pain, IMO, and not worth the hassle. One of these days I have to install a bias pot in the Bassman

December 17th, 2004, 01:04 PM	#5 (permalink)
Wally Friend of Leo's Join Date: Mar 2003 Location: Lubbock, TX Posts: 4,212	Bg, that SFDDR has a bias adjustment that is accessible from the underside of the chassis. The chassis does not need to be pulled to adjust the bias pot. A bias rite or similar tool would be very handy and would tell you exactly what current draw you are achieving. However, with care, one can adjust the bias according to what the player wants to hear within the range of safe current draw. Using a small screwdriver, one can adjust the bias one way (clockwise is viewing the bias pot upside down) until the plates begin to turn red. Back off of this setting as the red plates indicate too much current draw and the tubes will not live long. Just before the plates go red is the maximum current draw at which those tubes will work and survive. Distortion will occur most quickly at this setting...the amp will be 'hot'. Some folks like this sound, but know that tube life is shortest at this setting. Going away from this setting one is decreasing the current draw. The sound will progressively get 'cooler' with more headroom. At some point, the current draw will decrease to the point where the sound becomes very cold and sterile..much like a solid state amp...and harsh crossover distortion will occur. Toward this end of the range, tubes will have extended life. Within this range, one can pick what works for them. Also within this range is the 70% dissipation point at which most techs will advise that the current draw be set for good sound and acceptable tube life. This method I have described is especially handy if you are caught needing to change tubes but have nothing but a screwdriver and your ears with which to do the job.