Well I dont really know what 'biasing' is. So far I though it is only about applying equal voltage to tubes. The guy who was selling Minimax gave me as an example the situation you have 27VDC you should bias tubes at 13.5V each.
I thought I will purchase this:
http://beezar.com/oscommerce2/catalog/product_info.php?cPath=29&products_id=65
and this:
http://beezar.com/oscommerce2/catalog/product_info.php?cPath=29&products_id=75
Since the first thing is just a plastic screwdriver I will not buy it (is the normal screwdriver harder to use for biasing than bourns trimpot adjustment tool?). I will have to buy the multimeter since I dont have one. Or is it possible to bias tubes without it?
Well... maybe we should start from the beginning: how to bias tubes? My initial idea was to have a look at diyforums.org/minimax but now when I read their explanation of biasing I get confused.
Also: I just ordered Elpac 24VAC 750mA power supply as according to what the seller told me this is what Minimax needs.
My goal in my earlier post was NOT to prevent you from buying the tool, rather, how to work around the lack of not having one. It is most certainly worth owning and greatly simplifies the process.
You WILL need a multimeter to measure and set the bias. No way around it. They run the gamut in price from ridiculously cheap to amazingly expensive. For this purpose, you can get away with the cheap option as you are only going to measure DC voltage no greater than 30V and only need accuracy within a 1/2 a volt.
The bias on the miniMAX is set through a variable resistor call a potentiometer. It is used to set the starting voltage from which the tube will consider "zero". From this point, voltage will swing positive and negative and create the amplified signal. The bias point is picked to be right in the middle of the tubes sweet spot, whereas, it operates within the best of it's abilities. Yes, it is more complicated than this, but, this explanation is close enough for now. The take away is that the tube must be adjusted to be close to this sweet spot to sound it's best. So, if you want the amp to sound anywhere near what is was designed to sound like, you need to bias the tubes. Each tube is biased separately and should be as close to 13.5V as possible. Some users will advocate higher, and that is an option for future experiments, however, the design of the amp is for a bias point of 13.5V.
Setting it is easy and explained well on the miniMAX site. Set the multimeter to measure DC voltage, insert the probes into the appropriate test points and, using the tool, twist the screw on the appropriate trimpot (there are two) until the meter displays the desired voltage of 13.5V. Repeat the process for the other tube using the other test point. Realize,the bias will drift as the amp warms up. Check the settings once or twice after about an hour or so and then do not worry about again until you swap tubes.
Enjoy your amp.
I will not commit suicide after losing $2.
