One aspect is related to ionization that is strictly connetted with quality of the tube manufacterer.
My opinion tht is rilevant in the long term utilization of the tube, more than ac or dc filaments
There was a man in Turin, Mr. Doleatto, who had a little factory of tubes for military, three floors in a building. He died years ago.
He explain me that the quality of vacuum ( if the other components are fine) is the most important aspect of the tube for a long life.
Walter
My opinion tht is rilevant in the long term utilization of the tube, more than ac or dc filaments
There was a man in Turin, Mr. Doleatto, who had a little factory of tubes for military, three floors in a building. He died years ago.
He explain me that the quality of vacuum ( if the other components are fine) is the most important aspect of the tube for a long life.
Walter
So this could be mains to AC HF heater supply. Its a resonant invertor so generates sinewaves. R8 heater, R10 cathode resistor. You can duplicate as many secondary circuits as you wish to power as many output valves as you wish. Just to give ideas. Note its simulation only - the primary is not actually grounded but is at mains. Would need EMC input filter bridge, power supply caps - as well as attention to current loops in primary. The secondary side should be very EMC friendly. The transformer would be ferrite bobbin with inter primary, secondary screening.
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The "electronic transformers" for halogen bulbs were the first thing that came to my mind when I started reading this thread. Very interesting indeed how easily can one be modified to be used for heater supply.It seems nobody bothered to read the solution mentionned in post #5 at the very beginning of this thread. I have gone this route and it is much simpler than the convoluted contraptions I see around. I have built a few, both for me and for a friend, and they are dead silent at all power levels, be it in DH or IDH filaments. Silver-plated wire secondaries for DH filaments please
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Just dropping this paper here, for some experimenting in the future.
https://www.ti.com/lit/an/snoa665c/snoa665c.pdf
https://www.ti.com/lit/an/snoa665c/snoa665c.pdf
As a matter of fact it is so easy that I'm planning to try and design an HFAC supply to replace the B+ transformer altogether. These will not use the chinese halogen transformers at all - I don't trust them for that. Besides, their self-oscillation is only happening with a minimum load, which is not garanteed when supplying B+, for example think of the varying load presented by a class A output stage.
But this isn't all that complicated either, it's basically just a matter of replacing the passive oscillator with active driving of the switching devices. Currently gearing towards self-oscillating high-side/low-side half-bridge driver ICs. I have transferred the stock circuit in LTspice to study and already have a 20W toroid re-wired to produce HV, but haven't got around to design the driver yet. Plus I want to brush up on the safe implementation of line-connected rectifying circuitry. Probably happening within a year from now. Stay tuned
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It's a completely finished amplifier. https://www.worldradiohistory.com/A...m-Tube-Valley/Vacuum-Tube-Valley-Issue-15.pdf