| Electronics > Projects, Designs, and Technical Stuff |
| Strange AC current source..("variator"????) |
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| mikerj:
--- Quote from: ArthurDent on November 11, 2018, 05:06:44 pm ---mikerj - "Should a tube heater be driven with a constant current? I'd have thought the tungsten filament would have a positive TC, making constant drive undesirable. " If you check the reference in my post above, you will see how these constant current ballast tubes do a pretty good job to control a tube heater voltage. These ballast tubes were designed around the 1930s long before solid state voltage regulators were available to do a much better job. --- End quote --- I don't doubt that. I was responding to the post above mine, suggesting the OP builds a solid state constant current drive for the heaters. Constant current drive into a heater with a positive TC doesn't provide great regulation of it's output compared to voltage drive. |
| orolo:
Maybe a couple of depletion mode mosfets acting as a bidirectional current source? |
| coppercone2:
out of curiosity, what is the chassis temperature in the region you have available? |
| David Hess:
--- Quote from: orolo on November 12, 2018, 07:04:22 pm ---Maybe a couple of depletion mode mosfets acting as a bidirectional current source? --- End quote --- Or place a DC current regulator inside of a bridge rectifier. Or an AC shunt voltage regulator which is just two back-to-back zener diodes or a zener diode inside of a bridge rectifier could be used. There are lots of options including changing the heat voltage to DC making regulation easier. |
| SK_Caterpilar_SK:
Uff...I was away for a loong time.. The thing is not getting so unnaceptably hot inside. The chassi is huge and has a lot of ventilation. The tubes are EF800 (two) and one ECC83 (12AX7 as you may). The tubes are being run on low voltage purposely, the barreter was there because of the voltage fluctuations back in the days of 220V..you know your grandmother threw the oven on and all of the sudden the light were dimmer and your voltage in the wall was all of the sudden 200V. Voltages are relatively low on the tubes. The ECC83 has its filaments in parallel. The whole point of it was to reduce innacuracies in the masurement if and when the line voltages was fluctuating. It also has a dual diode for the AC range. That is a EAA91. |
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