For my next breadboard amp project, I wanted the ability to adjust B+ voltages but I didn't need DC voltage regulation.
On EBay, I found a Superior Electric Powerstat 10C rated for 120VAC & 2.25A.
The Powerstat variac autoformer will go between the AC Line IEC socket and the 800VCT B+ transformer that I recently purchased.
This seemed like a safer alternative that using a dropping resistor on the HOT side of the AC line.
DT 667 July 2019
I received the Powerstat 10C autoformer and installed it in my SE DC 6AQ5 project breadboard circuit on 7/9/2019. Wired up the B+ and filament transformers to run off one AC line IEC socket, each transformer having its own power switch and indicator lights. Important for a directly coupled circuit.
This robust variable transformer does the job and compared to my older TENMA 15A variac is totally silent during operation. No hum or mechanical buzzing of any kind.
Very easy to adjust B+ by turning the control knob which operates perfectly.
DT 667 July 10, 2019
I was searching for a B+ transformer that would allow me to generate 480-500VDC with a 5U4G directly heated tube rectifier.
EBay had a GE Plate Transformer : 800VCT @ 300mA Weight 20LBS for $52, so I bought it. The 300mA DC rating is probably a bit conservative.
Hammond has a similar model that weighs 12-13LBS and is rated at 535mA.
The GE transformer should function well in a SE 7B4 DC 2A3 stereo circuit, should I decide to work on that project in the future.
DT 667 June 2019