I've been reading about some of the unusual types of vacuum tubes such as the 6BN6 limiter/descriminator and the 6AR8 (and 7360 and others) balanced modulator and decided to run a 6AR8 through its paces. Here's a circuit that I came up with that works nicely as a DSB or AM modulator depending on the bias on the deflector plates. You can read about all of the gory details of my experiments here: http://www.solorb.com/elect/hamcirc/6AR8modu1/index.html Do any of you old-timers have ideas on why there seems to be a built-in imbalance in the tubes? First, I made sure the output coils and caps were balanced, then I tried two different RCA NOS tubes, tried swapping the deflectors and plates, did some resistive balancing of the input transformer windings, and even tried demagnetitzing the tubes to no avail. Adding a large capacitive imbalance to one side of the output circuit did help move the DSB null point to the center of the balance pot range, but it doesn't seem logical that it would be that far off.