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SET Asylum Single Ended Triodes (SETs), the ultimate tube lovers dream. |
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In Reply to: dc vs. ac posted by njjohn on February 18, 2004 at 03:33:32:
Konnichiwa,> Maybe we don't do dc right, that is a hypothesis.
Yup. It is.
> Sorry about the fact that I do have to question dc.
Well, one simple way to test this is to clip lead in external Sealed Lead Acid Batteries with an adjustable series resistor to get the heater voltage right and to make sure you have a pretty sustantial film cap across the heater at the valve socket. It will still be DC, but will show non of the various problems rectified AC invariably will....
Oh, before I forget, make sure you retain the loading of the mains transformer secondary by adding a pair of 8.2 Ohm power resistors across the 5v Winding of a 300B (or whatever is apropriate), as the added AC filament loads have effects on how the mains transformer behaves with rectification, several AC heaters quite effectively damp the inductive flywheel effect and switchoff ringing from the rectification while rectifying the heater windings adds to problems from the aforementioned effects.
I noticed that few people who use DC heaters treat the heater circuit with the same care they apply to the HT Supply section (and few treat the HT section with the care it deserves). Yet both are actually signal circuits, if you think about it. DC implemented with just a bridge and electrolytic cap will be problematic. Adding a crappy 3-Pin regulator often makes things worse, even current sourced DC heaters are not ideal until you apply added MF/RF filtering.
It can be done and is not THAT difficult to realise, but it is rarley documented, in fact I know of only three published sources that mention material effects in the heater circuits and how to address them and one of these sources is a german article documening one of my own amp projects (so it does not really count). The other two are SJS and Buddah....
Sayonara
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Follow Ups
- Re: dc vs. ac - Kuei Yang Wang 02/18/0407:51:50 02/18/04 (0)
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