Does it matter? Tool question...

bvmjethead · Post by **bvmjethead** » Sun Mar 12, 2006 9:03 am

I'm looking to get an amp biasing tool.

https://weberspeakerscom.secure.powweb. ... r_page.htm

http://biasking.com/two_kings.htm

I have a milti meter but I bought it from Sears and it's a Crapsman brand and I'm not happy with it. It's cheesy and works when it wants to.

Probably going to go somewhere and get a Fluke or some other decent brand.

Having said that I like the simplicity of being able to plug something in between the tubes and the chassis and it reads both bias and plate dissipation or whatever it is.... Sorry I'm not real savvy on the lingo yet, but I know there are two measurements I want to take and balance them out.

My question is, are there any other brands I should be aware of? Is there a better product? I currently am building a JTM45 but would like a product that I can grow with.

I'm leaning towards the Weber Bias Right BR-4 Octal with the V1 option due to price and features but I'm a complete newbie and really don't know jack.

Any help would be appreciated.

lp1987x · Post by **lp1987x** » Sun Mar 12, 2006 9:19 am

I made my own using instructions found here: http://hoffmanamps.infinology.net/chart ... urrent.htm and it works great.

bvmjethead · Post by **bvmjethead** » Sun Mar 12, 2006 9:50 am

Well thanks for that. It's certainly an option I had not considered.

Still interested in opinions on the commercially available tools I listed and others I may have missed.

Jimy · Post by **Jimy** » Sun Mar 12, 2006 10:55 am

I use the Bias King; like it, and can recommend it. However, I've never tried any of the other probes on the market, so I can't really make a comparrison.

You should read Randel Aiken's article "The Last Word on Biasing." It's a bit dense, but well worth your time. Somewhere in there, he recommends the Bias King and that's why I ended up choosing that brand.

Another bias probe that you might consider is the Alessandro Bias and Matching Meter It appears to be roughly equivilent to the Bias King Pro model in both price and features. Alessandro makes great stuff.

bvmjethead · Post by **bvmjethead** » Sun Mar 12, 2006 10:16 pm

Jimy wrote: You should read Randel Aiken's article "The Last Word on Biasing." It's a bit dense, but well worth your time. Somewhere in there, he recommends the Bias King and that's why I ended up choosing that brand.

I read Mr. Aikens article last night. It's very good I'm sure but well above my level of comprehension.

It's somewhat frustrating that I don't get this more than I do. It's quite a bit of learning to do and I'm probably being to hard on myself.

Andy · Post by **Andy** » Mon Mar 13, 2006 9:42 am

If you are using the 1ohm bias resistors (page5 of Georges instructions) you should not need a bias king/rite etc.. just a MM that reads in mV.

http://www.metroamp.com/forum/download.php?id=867

-Andy

Jimy · Post by **Jimy** » Mon Mar 13, 2006 11:03 am

Yep. There's more than one way to go about setting your bias. The method George outlines in his instructions is one of the best, simplest, and most straight forward. But if you read the Aiken article I mentioned, above, you'll see that every bias method has it's problems and that in the end Aiken recommends the Bias King type bias probe as the most effective, least problematic, approach. (He likes the 1R resistor technique too.) The reason I prefer to use the Bias King is that it works on ALL of my amps, not just the JTM45. I buy and sell a lot of old amps (mostly Fenders) and I don't want to have to modify a vintage piece by installing 1R resistors. With the Bias King, re-tubing is fast, accurate, and easy; and I never have to heat up the soldering iron.

So your point is well taken: you don't have to buy one of these things in order to build your JTM45 kit. But, depending on your circumstances, they can be a great investment and a really useful tool to have.

bvmjethead · Post by **bvmjethead** » Mon Mar 13, 2006 2:21 pm

It's not so much a question of need as want.

I'm assuming in order to bias with a MM you need to remove the chassis from the box, with the biasing tools you do not.If this is a correct assumption then I really want toll to bias.

I plan to keep my chassis bolted in the box as much as possible.

Andy I did build it according to the instructions. Are you saying that it's close with those resistors in place. I will be using the VA tubes at first but plan of putting some rather expensive NOS tubes in there after doing all the initial testing. Here is another point I think a tool will come in handy.

I just don't want to be flipping a chassis around on top of my bench with $800 in vintage tubes in it.....

Well.....lot's to ponder.

Jimy · Post by **Jimy** » Mon Mar 13, 2006 2:38 pm

Unless you drill a hole and install an external bias pot, you'll need to remove the chassis in order to adjust the bias... no matter what tool you use.

lp1987x · Post by **lp1987x** » Mon Mar 13, 2006 2:39 pm

With a tool you could check the bias without removing the chassis from the box. However, to adjust the bias, you will need to remove the chassis unless your amp has the adjustment screws on the back of the amp i.e. the Marshall JCM2000's.

lp1987x · Post by **lp1987x** » Mon Mar 13, 2006 2:41 pm

Jimy wrote:Unless you drill a hole and install an external bias pot, you'll need to remove the chassis in order to adjust the bias... no matter what tool you use.

You must be a faster typer than me.

That's not a bad idea for my current build though.

Jimy · Post by **Jimy** » Mon Mar 13, 2006 2:54 pm

A really slick setup for guys who like to swap tubes is to install external bias points and a locking external bias pot. I've seen some nice implementations over at the AX84 site. Done correctly, it's a really nice setup.

bvmjethead · Post by **bvmjethead** » Mon Mar 13, 2006 3:08 pm

Jimy wrote:Unless you drill a hole and install an external bias pot, you'll need to remove the chassis in order to adjust the bias... no matter what tool you use.

DUH!

I forgot the bias adjustment resistor is on the board.