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Saurav 11th October 2003 08:33 PM

FS: DC regulator boards for 2A3 (or other) filaments

Up for sale are a pair of boards I built to provide a DC regulated filament supply for my 2A3s. I did this mainly to try and reduce hum in my amp, and it didn't really do that (which means my hum is from other sources, not the filaments). The ICs generate a fair amount of heat and the underside of my amp is getting crowded, so I decided to go back to AC. The current regulated filaments sounded a little quieter and smoother, but I didn't want to put in the chassis/construction work required to ensure adequate ventilation.

The boards use MBR735 high current Schottky diodes, Elna electrolytic caps, and LT1085 adjustable regulators. You can configure this to be a voltage or a current regulator, depending on how you wire it to the sense resistor and the filaments (I can help you with the circuit connections and values if you want). I also have a pair of Hammond 6.3V/4A transformers that I used to power these with. A 2A3 filament takes 2.5V/2.5A, and these could supply that easily.

The circuits are built on Radio Shack PCBs, but I used point-to-point wiring so the PCB traces aren't carrying the 2.5A of current. You'll need to connect the transformers to the diode bridge, and the regulator to an external sense resistor and the filaments. You can also add a resistor between the capacitors to make a CRC filter, right now I just have both caps in parallel.

A list of the parts you'll get:

2x Hammond 166N6 filament transformers - 115V pri, 6.3V 4A CT sec (center tap wire has been trimmed and heat-shrink covered, but there's enough left over to solder to should you need it)
8x MBR735 35V 7.5A Schottky diodes with heatsinks
2x LT1085 3A adjustable voltage regulators with heatsinks
4x Elna 3300uF 35V capacitors

And as I said, I can help you with connecting this up (it's really easy to do).

I have about $70 in parts here. Asking for $40 shipped anywhere in the US or Canada, with free email consultation for any help you might need with these :)

If you've been thinking of trying DC current regulated filaments for your DHTs, here's your chance. I've already done all of the hard work, all you need to do is add these boards to your amps and solder a few connections.

Thanks for looking,

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