Bias Marshall Help

[GodWentPUNK]

Sorry for the cross post:

I need to re-bias my TSL100. I did this a couple of years ago and before I try again I was hoping to have a quick refresher.

I know that I have to use my ohmsmeter and by using the bias pot, turn it so that the left and right valves read close to the same value (which I remember was set to 87). I don't recal using any formula to caluate this value, I just turned the pot until the ohmsmeter read 87.

Does this sound right? Am I missing anything else?

joe...

[GodWentPUNK]

I did get this from Marshall:

SUBJECT: Bias Info/Procedure for JCM2000 series Marshall Amplifiers

THEORY OF OPERATION: We are setting the bias using the current method instead of cross over distortion method. The Bias PCB assembly is as follows:
PR1: Bias mini-pot adjustment for pin1 which is one side of the push pull amp (two output tubes in a 100watt amp and one output tube in a 50watt amp).
Pin1: Connected to the cathode of the output tube(s) which then goes through a 1 ohm resistor then to ground.
Pin2: ground reference.
Pin3: Same as pin1 but for the other side of the push/pull amp.
PR2: Bias mini-pot adjustment for pin3, the other side of the push/pull amp.


PROCEDURE:
1. Make sure amplifier is connected to a load with the proper impedance selected.
2. Power up amplifier on STANDBY and let the circuit stabilize for a couple of minutes.
3. Locate the male three pin molex connector CON2 with the two mini-pots (PR1 and PR2) on both ends found on the bottom of the tube bay. NOTE: This will be CON5 for the DSL201 and 401 and there is only one mini-pot PR1
4. On the appropriate connector(CON2 or 5) connect DMM (set to read mV) with alligator leads, reference common lead to center pin (pin2) on molex connector and positive lead to pin1
5. Take amplifier off of STANDBY with no signal, adjust mini-pot (PR1) closest to pin that the positive lead from your DMM is connected to and set it to the mV voltage that is listed in the chart below.
6. Repeat steps 4 & 5 for pin3 and until both pin1 and pin3 mV are the same.

BIAS CHART mV SETTINGS

(Pin1 and pin3)


TSL100/122 90mV