I'm building a PSU with a pair of CX381 valves, each of which is a half wave rectifier, forming a full wave rectifier.
These being very old valves I'd like to get the heater voltages as close to spec (7.5v) as I can. For that reason I plan to run each filament from its own separate transformer secondary (9v dropped to the right voltage by a variable power resistor). The filaments are joined to form the cathode which goes to choke/cap for smoothing.
Any reason not to do this? Excuse the sketchy sketch...
izzy wizzy wrote: ↑Thu Jun 20, 2019 4:23 pm
You could still run the fils in parallel as you'll be using the series resistor to trim for the right V across them as a pair.
Fabulous looking valve.
Cheers,
Stephen
Yeah but if I want to trim each valve heater voltage individually then I need separate secondaries and resistors.
Whether that is the right thing to do is another argument of course, but let's sidestep that for now. First I want to make sure what I've sketched out is valid.
izzy wizzy wrote: ↑Thu Jun 20, 2019 4:23 pm
You could still run the fils in parallel as you'll be using the series resistor to trim for the right V across them as a pair.
Fabulous looking valve.
Cheers,
Stephen
Yeah but if I want to trim each valve heater voltage individually then I need separate secondaries and resistors.
Whether that is the right thing to do is another argument of course, but let's sidestep that for now. First I want to make sure what I've sketched out is valid.
What you've sketched is valid.
If they're in parallel you get the exact same result as you'll be trimming for voltage across them both and you only have to do it once. I don't see the need to make it more complicated even given your reasons. I've done similar for MVs.
Indeed. This is his new PSU, which I'm now wiring up. Like his amp, the valves are all Cunningham globes, 4 x CX381, 4 x CX380. 500 year old burr elm...
