Would someone be able to help a brother out finding the grid current draw during A2 operation of a 2A3? Can't seem to find a datasheet with positive grid information. I would like to needlessly shunt regulate the negative supply of the source follower with a VR tube, for no other reason than it is pretty, and I have the space. I am concerned though, that during A2 operation, too much grid current will need to be sourced extinguishing the regulator.
The regulation of negative supply is unnecessary if the B+ (and the source follower positive power) is unregulated.
If all unregulated, and the negative supply is generated from the same HV secondary as the B+, the mains voltage fluctuation affects both -almost- equally, so the bias "wandering" not significant.
If all unregulated, and the negative supply is generated from the same HV secondary as the B+, the mains voltage fluctuation affects both -almost- equally, so the bias "wandering" not significant.
I had a bonehead moment. Any grid current needed won't be sourced from the VR tube. Even if it pulls an amp, the regulator will be fine. I hadn't drawn it out to look at the actual current paths. Thanks for the responses, fellas.
I have several class A2 amps, so he probably mean A2, when he said it.
The term class A can be A1 or A2, just as class AB can be AB1 or AB2. The distinction between the 1 and 2 is the same for both. In class AB1 or class A1, NO grid current flows. In class A2 or AB2, grid current flows for all, or part of the drive cycle.
Most single ended amps using 811A or 833A tubes are class A2 since the grid must be driven positive to get current flow at relatively low B+ voltages.
The 2A3 responds well in class A2, though I have not measured the peak grid current.
6a3's are what I have ordered. The idea is to use the SLA batteries I have on hand for the filaments. Another major selling point for the Sovtek 6A3 is the mono plate construction. I have never heard a 2A3 or it's kin, but I may already have bias against dual plates.