I was thinking of taking a big step and getting into building tube effects, and I thought the Tube Preamp would be a nice project to build since it's not horribly complicated.
I was looking at the scehmatic for the F-2B at GEO and i was wondering what the secondary voltage on the transformer should be where it's feeding into the voltage regulation section for the tubes.
TIA!
Phillip
That circuit looks like a great introduction to tubedom. :D That's more or less the first two stages of a Fender style preamp.
You could use a wide range of voltages there. A 115 to 230V step-up transformer would be a good choice but you could sure run the tube a bit hotter than that. Check out recent threads on Doug's FireFly for more info there.
Just to throw some numbers out... you will need to supply 6.3V @ at least 300mA for the filaments (use at least 500mA to be really safe). For the HV side, it looks like that schematic may call for something around 150V since it uses a voltage doubler. Any transformer that puts out 150 to 250VAC is fine if you're using a SS bridge rectifier (don't try that with the schematic as shown, you'll have to rip out the doubler). Fender runs those stages at 270V in the Super, but that's after a few RC filters and a GZ34 rectifier, and a bunch of other tubes so they start with 360V from the transformer. There's a lot of latitude, but the voltage will affect the tone. There are "sweet spots" for almost every circuit but it's going to sound good any way you slice it. :D
Best of luck and welcome to tube land!
Take care,
-Peter
Thanks Peter. Now to find the right transformer...
Phillip
My pleasure. :D
You can always use a filament transformer with dual primaries in reverse too. Start with the 6.3V from your filament transformer and then wire that into the second transformer's 6.3V "secondary". Connect the two "primaries" in series (I put that in quotes because it's being used backwards), attach the outs from that to a bridge rectifier made of 1N4007s and feed the positive to the first filter cap, eliminating the diodes in the schematic. There you go!
The next big step is to get an output transformer, a 12AU7, and wire up the output stage of Doug's FireFly for the full-tube experience. ;)
Take care,
-Peter