Bias probe

[überfuzz]

I stumbled over a 'bias probe' on the net. It's seems to turn biasing tubes into a 2 min job. Has anyone here ever used one biasing his/her amp? Liked it or disliked it?

I found one, thinking of placing an order. bias probe + plate voltage tester

All my amps have fixed plate voltage, which is well documented. So I don't really need a plate voltage tester, but I can't resist it. Then again, measuring the plate voltage might point out gnarlys.

[Enzo]

I would find it very surprising your plate voltages can be determined from spec. I can;t think of any comercial guitar amps with regulated B+. The schematic may say 480v or something, but there is also usually a note that it may vary by 20%. Just changing the tube current with the bias setting will affect the B+ voltage. SO if the plates sit at 480v with 20ma through the tubes, and you crank it up to 38ma, that 480v will fall.

yes we use and discuss bias probes all the time. I suggest use the search function here, and it will find you many such discussions.

Since it is important to know both current and voltage, a bias probe that measures both will be easier to use than a current only meter.

[tedmich]

thats a good probe! The V->mV scaling is a good safety feature, I believe the Eurotubes probe has no scaling so you can get B+ at the banana plugs (yikes!)

[überfuzz]

I'll get me one of them then.

Oh, and thanks Enzo for the cheerful answer.

[Sonicbloom]

I ordered a cheap bias probe from eurotubes.com and had the center plastic piece brake off inside my amp and cause a string of problems. other then that it works fine.

[defaced]

That center plastic piece will also break off of your tubes. Not that I've ever had that happen...

[überfuzz]

I sat down and tinkered with some scrap parts. I ended up with a probe that helps me measure plate voltage and current. (With a little help from my... multimeter.)

[CharlieP]

I ordered a cheap bias probe from eurotubes.com and had the center plastic piece brake off inside my amp and cause a string of problems. other then that it works fine.

If mis-used anything can break. Use with care, it is a delicate instrument, not a grease monkey tool!