Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TenderTendon on February 09, 2023, 11:43:01 pm
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I have been pulling my hair out trying to figure out how the optional DC heater circuit in the attached schematic would supply adequate voltage (6.3vdc) to valves 1 and 2. Every time I look at it, the best I can see it supplying is 4-5 volts at best. Could someone please explain how this works? Thank you.
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6.3Vrms = 8.9Vpk. The FWB will produce 8.9vdc - 1.2v (two diode drop) = 7.7vdc unloaded. The two tubes will need .6A current for typical operation. This .6A load will cause the unloaded 7.7vdc to drop, probably to around 6V, maybe higher, certainly enough to heat the tubes properly.
Why do you think it will only supply 4-5 volts?
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6.3Vrms = 8.9Vpp. The FWB will produce 8.9vdc - 1.2v (two diode drop) = 7.7vdc unloaded. The two tubes will need .6A current for typical operation. This .6A load will cause the unloaded 7.7vdc to drop, probably to around 6V, maybe higher, certainly enough to heat the tubes properly.
Why do you think it will only supply 4-5 volts?
Christ.... I can't believe I wasted all that time, simply because I forgot about the RMS of the wave. I was working with 6.3v peak to peak. :BangHead: Thank you for the lesson!
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8.9Vpp should be 8.9Vpk