Mains Transformers 0-6.3V,3.15V-0-3.15V different

[pc1093]

hi all,

what's different between 0-6.3V and 3.15V-0-3.15V in the main transformer?
most of heaters connect to  3.15V-0-3.15V, could I use 0-6.3V?

[d95err]

You can create a ”virtual” center tap for the 0-6.3V winding by using two 100 ohm resistors, to get a balanced ground reference.

This works fine (some say it’s even better than a real center tap).

[kagliostro]

You can also go further and use a 220R pot instead of the fixed 100R resistors (connect the wiper of the pot to ground)

this way you'll have the opportunity to rotate the shaft of the pot for the maximum hum rejection

Franco

[jjasilli]

3.15V-0-3.15V: if you don't use the CT, then it's functionally  a 0-6.3V tranny.

[pc1093]

I find a Transformer with 250-0-250. My Amp just need  250V(before Smoothing and Filtering) for the HV. Would I only use 250-0 wire for the HV and insulated the other 250 wire?

[kagliostro]

...... Would I only use 250-0 wire for the HV and insulated the other 250 wire?

NO, connect CT to ground and rectify using two diodes



http://www.valvewizard.co.uk/bridge.html

If you want (and circuit requirement permit) you can use a 6.3v Vacuum Tube Rectifier instead of the pair of diodes, but rectifier must be indirect heated



Tubes like the EZ81 http://www.r-type.org/pdfs/ez81-1.pdf

are fine for this use (if the voltage and current spech are within the requirement of the circuit of the amp)

Franco

[pc1093]

...... Would I only use 250-0 wire for the HV and insulated the other 250 wire?

NO, connect CT to ground and rectify using two diodes



http://www.valvewizard.co.uk/bridge.html

If you want (and circuit requirement permit) you can use a 6.3v Vacuum Tube Rectifier instead of the pair of diodes, but rectifier must be indirect heated



Tubes like the EZ81 http://www.r-type.org/pdfs/ez81-1.pdf

are fine for this use (if the voltage and current spech are within the requirement of the circuit of the amp)

Franco

In this connection, is it 500V ?

[shooter]

follow the link for good read
will answer that question AND why 

http://www.valvewizard.co.uk/bridge.html

(I'll give you a hint, NO:)

[pc1093]

follow the link for good read
will answer that question AND why 

http://www.valvewizard.co.uk/bridge.html

(I'll give you a hint, NO:)

I got the point.
In this connection, I have 500*square root of 2 voltage.
In this connection, have 250*square root of 2 voltage.
right?

[sluckey]

right

[kagliostro]

Right

Assuming the transformer used with the FWB has a CT (not connected to GND) and Is the same transformer used with CT connected to GND and the pair of diodes of the second example, not a generic PT without a CT


Franco