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In Reply to: RE: Have DIY HiFi Filament Supply and questions posted by NewbieBaby on April 27, 2008 at 14:34:55
Hi,
Just cutting to help to unwedge this one....
From my own work with these supplies there is no way this will ever work the way you are trying.
With a 6.3V AC winding you can get a decent 5V, but no way you get 6.3V. and adding resistors in SERIES will not increase the voltage, it will LOWER IT. Basically, you lack sufficient voltage, sweet and simple.
When using the supplies you als need to disconnect the resistor from the centertap of the heater winding and connect it to the positive or negative side of the heater (positive recommended). This is fundamentally essenial to use any kind of DC supply, be it Guido's or the DIYHFS one.
You have a number of options now:
1) Find a way to add a few turns and thus a few volt to your existing transformer for each section, this is easy with torroid mains transformers (around 4 turns per volt), but near impossible with E/I ones such as in your ST70.
2) Get a seperate transformer to add these few volts, you might find a transformer with two 2.5V windings (I seem to remember hammond makes one) with at least 3A each and connect these windings in series with the existing 6.3V ones, to get enough voltage to use 6.3V DC heaters (observe polarity).
3) Get a completely seperate transformer for the heaters, something like 9V/3A + 9V/3A should work well.
You really do not have much of an option to switch to 2A3's without a new heater transformer, unless you wire the heaters in series, which can be dicey, as the voltages rarely balance all that well.
Basically, the ST-70 is a very poor experimening platform, it is just calculated way to narrow to leave any flexibility.
Ciao T
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