How to Bias your tube amp with FLUKE multi meter?

[hopkinWFG]

Hi there fellow tube amp enthusiast... i would like to know how could i get to bias my tube amp just using Fluke meter without external biasing points? i have a set of EL34s here running at 50 watts and i'll like to have at steps at the testing points to bias the tubes and also in both mA and mV settings.. any kind soul would like to share? thank you

 

[duesentrieb]

Fluke to 200mA DC current. Red probe to PIN 3 of the powertube socket, black probe to middle of output transformer. Gives you the reading for one side. The other side would be the other PIN3 also to middle of the OT. Middle of OT in many amps is located at the HT fuse (Marshalls f.i.).

 

[Mudder]

Deuse has a video on youtube how to do it if you need it.

 

[duesentrieb]

Yeah, you just need to locate the OT primary wires and measure both sides. Keep in mind that you have lethal voltages there . . .

Into a non PCB amp I would install 1 Ohm low-% resistors between PIN8 and ground and read the milli Volts instead.

 

[hopkinWFG]

Fluke to 200mA DC current. Red probe to PIN 3 of the powertube socket, black probe to middle of output transformer. Gives you the reading for one side. The other side would be the other PIN3 also to middle of the OT. Middle of OT in many amps is located at the HT fuse (Marshalls f.i.).

Thanks alot buddy !! that would be your mA DC current measurement? but i have come to see a particular video which he did it with the grounding test probe in reference to ground connected to the chassis and reading is in mV is that the way to bias it in mV ? if so which is the other positive point i would get my multimeter probe on to test in mV range? would it be essential to know of your mA or mV readings when you bias you tubes? or i would just have to do it on either one means ie: mA or mV ?

 

[Digital Jams]

Well I'm all flush in the face listening to Olaf biasing an amp

 

[duesentrieb]

 

[duesentrieb]

Fluke to 200mA DC current. Red probe to PIN 3 of the powertube socket, black probe to middle of output transformer. Gives you the reading for one side. The other side would be the other PIN3 also to middle of the OT. Middle of OT in many amps is located at the HT fuse (Marshalls f.i.).

Thanks alot buddy !! that would be your mA DC current measurement? but i have come to see a particular video which he did it with the grounding test probe in reference to ground connected to the chassis and reading is in mV is that the way to bias it in mV ? if so which is the other positive point i would get my multimeter probe on to test in mV range? would it be essential to know of your mA or mV readings when you bias you tubes? or i would just have to do it on either one means ie: mA or mV ?

When you read at the output transformer primaries, set the DMM to mA DC.

When you have an 1 Ohm Resistor installed between 8 and ground, read across the resistor and set DMM to read mV DC.
(U = R x I - in this case R = 1 Ohm, so U = I, you know)

HTH

 

[hopkinWFG]

Fluke to 200mA DC current. Red probe to PIN 3 of the powertube socket, black probe to middle of output transformer. Gives you the reading for one side. The other side would be the other PIN3 also to middle of the OT. Middle of OT in many amps is located at the HT fuse (Marshalls f.i.).

Thanks alot buddy !! that would be your mA DC current measurement? but i have come to see a particular video which he did it with the grounding test probe in reference to ground connected to the chassis and reading is in mV is that the way to bias it in mV ? if so which is the other positive point i would get my multimeter probe on to test in mV range? would it be essential to know of your mA or mV readings when you bias you tubes? or i would just have to do it on either one means ie: mA or mV ?

When you read at the output transformer primaries, set the DMM to mA DC.

When you have an 1 Ohm Resistor installed between 8 and ground, read across the resistor and set DMM to read mV DC.
(U = R x I - in this case R = 1 Ohm, so U = I, you know)

HTH

Arr ohms law V=IxR ok got it haha thats of the very basic lol