Bias Test Box

[Ron Worley]

Thought I'd share something I built yesterday to help biasing my first build. I hate using the transformer shunt method (I know, what a wuss), but didn't want to solder in 1 ohm resistors either.

I had a minor epiphany that the resistors need not be in the amp, so I built this little test box for less than $5..

You will need a set of DMM test leads with spring clips, and an extra red test lead with the same clips- Radio Shack sells a cheap set. This allows a no-hands / moving probe in the amp biasing (other than tweaking the bias pot).

I also modified the grounding wire on the power tubes to go from the ground lug to the lower hole of the pin 1 lug instead of pin 8 (my lugs have 2 holes, so this worked well). I soldered a jumper to the upper hole of pin 1 that will go to the lower hole on Pin 8 (the diodes are on the upper hole) I left the jumper bend out away from pin 8 for biasing, and will solder in when I done.

This worked a treat- it only involves moving the DMM positive probe from the right positive jack on the test box to the left positive jack. Very fast, very safe.

Ron

[Ron Worley]

More pics....

[Bob-I]

Looks really complex. I'll just solder in the 1 ohm resistors

[Ron Worley]

Not really.. it's a compromise between the installed bias test method and the KF official Wreck configuration... Your choice....

I built it to be ready to deal with Fenders, which I do more work on (so far)

Ron

[Ron Worley]

OK, apparently, this was a stupid idea.. I just wanted to make biasing safer.

I've seen sparks and stars in a Fender..... didn't really like it....