Biasing issues on Randall 667

JacksonRhodes

New member
I have a Randall 667, here are the instructions from the manual

BIAS CONTROLS

This is a powerful feature and tool for exploring more tonal possibilities with the 667 amplifier. You can mix and match different tube types together for an almost unlimited range of tones. More on this later. Since there is individual bias adjustment for each tube, there is no need to obtain matched tubes! 667 will accept EL34, 6CA7, KT77, 6L6, 5881,
KT66, 6550, KT88, KT90, KT100/120 type tubes and any other derivations of the above. The output power will range
from 100 to 180 watts RMS depending on the output tube selection. The added benefit of having output tubes fused in
pairs is in case of tube failure, you will be able to finish your gig. Only a small volume reduction and slight tonal
change will occur. Biasing the 667 amp is simple and does not require removal of the chassis. You will need a simple voltmeter or digital multimeter set to the lowest DC voltage range, typically 200mV (millivolts). Please note that some meters display may indicate 25.0 for 25 mV and others may display .025 for 25 mV. Make sure you know your meter and refer

back to the meter’s owners manual to be certain. Then follow the these directions: Unplug any cords from the INPUT,
make sure the MASTER volume control is turned all the way down, counterclockwise. Turn all the bias controls all the
way down, counterclockwise. Connect a load to the appropriate speaker jack, plug in the AC cord and turn on the
amplifier. Wait a few minutes then put the STANDBY switch in the up position. Put the black negative probe lead of your meter into the common tip jack. Place the positive red probe lead in the red tip jack of TEST 1. Referring to the recommended bias settings below, slowly adjust the corresponding bias pot while paying attention to its sensitivity. Make a note of your bias setting if you are using 2 or 4 of the same tubes. Repeat step 2 for TEST 2, TEST 3, & TEST 4. Then recheck and make further adjustments as necessary. Once the bias is set, you are ready to play.
Recommended Bias Settings:
EL34/6CA7/KT77 6L6 /5881/KT66 6550/KT88 KT120
34mV to 40mV 32mV to 38mV 38mV to 45mV 45mV to 50mV
Note: The upper range of the recommended bias settings should be considered a maximum setting. Feel free to experiment within the given ranges to suit your taste. It is normal for tubes to drift a little, especially when they are new, and will stabilize after a few hours of use. Also, bias will drift with variations in AC line voltage. This is not a big deal so don’t get obsessed by constantly checking the bias to keep it at your chosen settings. To balance out the currents of the output tube when using 4 of the same type of output tubes, place one meter probe (black or red) into TEST 1 red tip jack then the other meter probe into the TEST 4 red tip jack. Then adjust either one of the corresponding bias pots to get a 0 reading on your meter. Repeat the above for TEST 2 and TEST 3. If you are using 2 different output tube types, (e.g. 2-KT88 and 2-EL34), place the 2-KT88s in either V1 and V4 or V2 and V3 positions, then the 2-EL34s in the remaining positions and follow the above procedure to balance out the currents.


PROBLEM IS AS FOLLOWS.
When I put the red tip of my multimeter into the 4 seperate tip jacks, V2 is the only one that will read in Millivolts on my meter, v1,3,4 all show volts only. My multimeter has a auto feature so it will show the power as what it is. The multimeter works on my other amp and I have checked the amp with two other multimeters they read the same. With the biasing controls set to the lowest setting it shows volts as 1-2 , except for V3 which shows millivolts as 1-2. When I turn the bias controls as high as they will go the v1,3,4 will read 30-40 volts. V2 can be biased to the 34-40mv.

Not sure why it is doing this? All of the tubes are el34
 
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