Tube DIY Asylum

RE: Switching PS for filaments

66.30.91.130

In Reply to: RE: Switching PS for filaments posted by gluca on June 28, 2008 at 12:32:23

I've been thinking about using switch mode supplies in my next amp too, only because I want to make a really small one. These are my thoughts on the heater supply:

switching frequency - needs to be high enough so the audio amplifier has already rolled off long before it gets to the switching frequency. The heater-to-cathode capacitance will probably pass the high frequency stuff right through, so you want to be sure that you don't have any real response from the amp at that frequency. Subharmonics probably won't be a problem, since the tubes are a high enough load that the switcher output should ever start doing subharmonics.

isolation - I don't know if you are looking to go DC-to-DC or AC-to-DC, but in the former case, there are lots of modules out there that are not isolated. I'm guessing you are going AC-to-DC, in which case they are probably all isolated for safety reasons. This only _really_ matters with direct heated stuff. There's a good case to have it with indirect heated also, but it isn't as critical (I don't think so anyway).

Check it when it's hot. I had one cheapo supply I used for something and as the temp went up the output voltage changed significantly. As the amp tends to get hot as it's been on for a while, good to just keep an eye on it to make sure it's behaving.

Anyway, just my thoughts on it.
-Nate

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