Hi all
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...
Parallel heaters for CX381 rectifiers
- izzy wizzy
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#2 Re: Parallel heaters for CX381 rectifiers
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
Fabulous looking valve.
Cheers,
Stephen
#3 Re: Parallel heaters for CX381 rectifiers
Yeah but if I want to trim each valve heater voltage individually then I need separate secondaries and resistors.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
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
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#4 Re: Parallel heaters for CX381 rectifiers
What you've sketched is valid.RhythMick wrote: ↑Thu Jun 20, 2019 4:52 pmYeah but if I want to trim each valve heater voltage individually then I need separate secondaries and resistors.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
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.
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.
Cheers,
Stephen
#5 Re: Parallel heaters for CX381 rectifiers
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...
- IslandPink
- Amstrad Tower of Power
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#6 Re: Parallel heaters for CX381 rectifiers
We are not worthy !!
"Once you find out ... the Circumstances ; then you can go out"
#7 Re: Parallel heaters for CX381 rectifiers
My woodwork skills are certainly not up there. Actually making anything look vaguely presentable is a challenge to me.