Friedman Smallbox 50 Layout

[purpletele]

I came across a layout diagram for a Friedman Smallbox 50.  I have been gassing for one of these amps and started looking for schematic and layout info just for fun.

Maybe someone can design a turret board.  Still searching for a schematic.

[shooter]

Maybe someone can

I got this far 

http://el34world.com/Forum/index.php?topic=23937.0

[purpletele]

Maybe someone can

I got this far 

http://el34world.com/Forum/index.php?topic=23937.0

I couldn't get into the Tube-Town Forum, still trying

Small box 50 Schematic

http://www.tube-town.de/ttforum/index.php?action=dlattach;topic=21032.0;attach=49804;image

[Ledzepp007]

For most of us, we’d have to tap the B+ to get the ~10-15VAC needed for the DC heaters.

[sluckey]

For most of us, we’d have to tap the B+ to get the ~10-15VAC needed for the DC heaters.

How would you do that?

[Ledzepp007]

For most of us, we’d have to tap the B+ to get the ~10-15VAC needed for the DC heaters.

How would you do that?

Great question. I suppose in theory one would treat it like a second bias supply: use a sufficient dropping resistor to get the VAC to an acceptable range, rectify it, smooth it, and then regulate it to 12VDC. The max VDC for that regulator is 35, so the rectified, smoothed voltage would need to probably be between 15 and 25 VDC.

I suppose one could use the 6.3VAC tap and a voltage doubler, but I’m not sure you’d be able to handle the current of three 12AX7 filaments.

[sluckey]

Each 12AX7 will want 150mA to light up properly. I doubt you'll be able to get that kind of current from a typical high voltage winding after going through a resistor sufficient to drop the voltage to 12V.

[Ledzepp007]

So one would either need to do a custom transformer, have a separate filament transformer, or use the voltage doubling technique (with a transformer that has a sufficiently high current rating for the heaters)?

[sluckey]

All those methods are viable options. Just rectifying/filtering a 6.3VAC source is fine too. Just use a single low resistance/high wattage resistor to drop the voltage to 6VDC for the tubes. No need for a regulator since the load current is constant.