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In Reply to: RE: Fuse for PAS-2 Transformer Replacement posted by patknk939 on May 09, 2015 at 15:52:48
Hi 1973Shovel. I checked the bottom of the cap board. While the trace from "out to xfmr" runs the same way as you indicated, the trace from "120V in" is not. It runs to the small capacitor (right next to the fuse) that connects to the fuse. As for the half-amp fuse, I don't know why it is not the 300mA as the schematic shows. The fuse is there when I bought the board. In fact, the two caps (rectangular ones on left of the schematic) on the actual cap board are each 0.22uf, not 0.1uf showed.
Follow Ups:
The cap is likely a high-voltage cap between hot and neutral AC. I'm confident your Audio Sound Lab board provides for the PAS to be fully fused as it is configured.
They likely upped the fuse value due to too many opening during power-up. 0.5A should be fine, and still offer you protection in the event of a short.
One question I didn't ask at the beginning, but have been curious about. Is there any particular reason you are replacing your PA211 transformer? Moving it externally, I understand. I did that on my Vorhis Last PAS, because I needed the room internally. I'm still using my original PAS transformer, and that's with somewhere around 80,000µF on the filaments. I just don't want to see you spending money on something you may not need.
Good luck with your project.
"You won't come back from Fletcher-Munson curve"-Jan and Dean
Replacing the PA211 transformer is not because it has problems. It`s that I thought the transformer is aged and the new PA211 is better constructed and is a little bit more powerful. So, hopefully it could be a little bit of upgrade for the PAS with the new transformer. Thanks for your time.
I would save my money.
The newer PA211 might have better specs, or whoever's selling it might claim it's better. But there are posts (you'll have to search) claiming some of the new production PA211s out there aren't as good as the original. I know, because I considered buying one to try building a dual-mono (one transformer per channel) power supply for my Last PAS. After reading what I read, I passed.
If you want an inexpensive upgrade, tweak, or whatever you'd like to call it, I would suggest adding capacitance to the filament supply. You could replace those two 2200µF caps on your board with the Nichicons I've linked below, but there's no need to. As long as you have room, you can add the extra caps, and simply wire them in parallel with the existing caps. Secure them with a bit of silicone, and you're good.
I'm not one of those "magic wire" guys, who claim they hear major improvements with every change. But I've never failed to hear an improvement when adding a significant amount of capacitance to a stock (or nearly stock, as yours is) PAS filament supply.
Good luck, and you're very welcome. Thanks for saying "thanks"!
"You won't come back from Fletcher-Munson curve"-Jan and Dean
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