Name:    Steve Kennedy
Email:   steve@pacair.com  
Subject: mm 2-10 65 bias
Thread:  35
Time:    Thu, 27 Dec 2001 00:11:14 UTC

If you are using matched output tubes (which I assume you are) then you probably have another circuit element that has aged in the opposite direction from its counterpart.


In the solid state phase-splitter version, check the 3.9 ohm 1 watt virtual cathode resistors connected to the transistor driver's emitters. If these are just a little off the tubes can be unbalanced. The same goes for the driver transistors (one might be leaky). It could also be the 220 ohm resistors going to the first grid.


Anything that controls current flow through the tubes OR is in the current path of each tube can cause a mismatch if they are not themselves balanced (same values).


On the tube phase-shifter version, look at the 330k resistors going to the first grid.


Generally, if you probe around the circuitry looking at voltages and comparing the two theoretically identical circuit halves you can probably find something unbalanced and then can deal with it.


If all complementary components are identical to each other, then the circuit node voltages should be identical and the bias will be identical (or at least really close... within 1mA should be acceptable and achievable).


Steve