Tsarina, over the top
Anastasia–don't ask me where the silly name comes from!–is a pretty much over-the-top preamp put together of three modules: line stage, phono stage and power supply.
The line stage consists of separate input modules each with its own input transformer. The step up/down ratios of the transformers are adjusted to each source, the range goes from 2:0.5+0.5 to 1:3.5+3.5. The signal is amplified symmetrically with a differential 12B4 stage (the tubes were matched very precisely on a curve tracer). The 12B4 are followed by a 3:2 output transformer and an autotransformer volume control. The signal levels are optimized for the BSS FDS 366/Betsy combo (see "Betsy")
The phono stage is fully balanced and uses a Tango LCR module for the RIAA-EQ. The signal is stepped up with an input transformer and split to the grids of the first gain stage. Two 7462 ceramic planar triodes (differential with a common CCS in the cathodes) are choke-loaded and direct coupled to a 5687 triode which again feeds the LCR module via a 4:1 transformer for impedance correction. The lost gain is recuperated after the LCR with a 1:2+2 transformer which couples the phono stage to the grids of the line stage tubes.
Anastasia and Betsy share a common power supply. The PSU is huge (4 HU 19") and heavy as a rock. No wonder, there are plenty of tubes to be fed with plenty of current… Lot of the weight is due to the fact that all B+ and heater voltages are LCLC filtered. Which probably wasn't nescessary, but certainly doesn't harm the sound… Since clean and stable DC is especialy critical for the phono stage, each of the two stages is fed by its own shunt regulated B+.
And where's the picture?
I can't–or won't–show a picture of Anastasia because a) she's a breadboarded rats' nest and b) the relay control for the input selection isn't ready and c) because the real chassis has yet to be built. You know the story… Instead I show you one of those tiny 7462 ceramic planar triodes used in the phono stage–the scale is centimeters, not inches! I had to solder them to IC-sockets in order to match them on the curve tracer. However, the butt-ugly messy breadboards work and the whole thing sounds amazingly good. There's still a lot of work to be done, though. So stay tuned…
At least you can download the schematics of all of Anastasia's circuits: