Setting up the right PS

[fikri]

Hi ! i need help to set up the right PS for me:

I have a 0-18;0-18 3A toroidal transformer that i want to use to power up 4 preamp tubes fillaments, and 6  relays switch. But i have to bring the voltages down to 12V DC first. I dont want to use regulator ic because i want to prevent heat. Could you help to set this up for me ? Thanks !

[Peter Snowberg]

If you don't use a regulator then your other option is to use a big resistor. Either way you're going to get lots of heat.

4 preamp tubes (assuming 12A_7 types) will require either 1.2A @ 6.3V, or 600mA @ 12.6V.

Rectifying 18VAC will give you about 24-25VDC (depending on the diodes used). With that voltage available you could use the 12.6 volt heater connections (heaters powered by pins 4 & 5; pin 9 left unconnected) and simply put two tubes in series to make a 24V heater string. Now place the other two tubes in series like the first two, wire the two strings in parallel, and there you go. For the relays you could just use 24V coils and now you don't have to drop the voltage.

CAUTION: that wiring will pull only 300mA out of the transformer which is rated for 20 times that much. This means the actual voltage from those 18V windings will probably be a good bit higher than 18V and that throws a monkey wrench into the above plans.

I would use a better suited transformer instead.

[fikri]

Thanks a lot peter  I know it is my fault to bought that silly toroidal  . I tought it could be fun, but what was going here is just messin' up the whole circuit ! Maybe i should change the transformer, all i need is just 0-12V 3A with two separate regulator for fillaments and relays, am i right ?

Thanks again.

[RDV]

However that's a dandy transformer to build a chipamp!



RDV

[fikri]

However that's a dandy transformer to build a chipamp!

Thanks ! BTW What is a chipamp RDV ?