Marshall 900 prob

[stokes]

As for the issue of "dropping" the lead,use clip leads.There is always danger when working in a live chassis,and like Amp Kat pointed out we cant always take the safest route due to different topology issues in a given amp,so knowing all the different techniques,as well as the dangers involved using each,is important.TD-I have the same "home made" rig,I also have a switch to switch between the plate measurement and the 1 ohm cathode,very handy.And the price of the commercially made unit is way to high.

[Bruce / Mission Amps]

Get a Compu-Bias and stop messing around.

If you want to try the best biasing tool I've used, here it is:

http://www.compu-bias.com/

It does everything for you! The cathode current, the plate voltage, plus, if you are like me and like to see it in DC watts, it does the math too!!
It is very very well priced and much better then just about anything out there.

I've been working with Randy for about a year on this project and it kills.

Read about bias, bias voltage, idle current and biasing here:
http://www.compu-bias.com/bias.shtml

Bruce

[Mark Black]

Wow - there it is - just like I wished for!

Price is pretty fair for such a specialized piece of test gear too. Maybe after the holidays...

[Mars Amp Repair]

CT current method;
Folks,
Am I missing something here...
I find on most amps it is relatively easy to merely remove the CT of the OT & insert my milliameter there. Many amps have a spade type connectors for the OT which makes it even easier. You can even just slide your probe into the spade lug end with no troublesome alligator leads to mess with and a hook probe on the other end of the meter probe usually connects easily to the male spade lug on the pcb.
It measures pretty evenly compared to the shunt method..I would think it would even be more accurate.

Bruce, I'll have to check out the Compu-bias tool, thanx for that link. Always looking for easier ways to get the same thing done...time is $$ as we all know.

I also need to stop by some day & meet you. We're in the same neck of the world, ya know.

thanx, glen