[Leadman]

Hello, I want to build an amplifier with 3 12ax7 preamp tubes and 2 5881 power tubes. I want the power to be higher than a Deluxe reverb, something between 30w-40w.

My questions are regarding the TT135VA toroidal power transformer. Would it be enough for this type of circuit?

The transformer has 2 300-0 windings at 150ma, each of these windings would give me a current intensity when rectified of about 110ma. By joining them I could have a 300-0-300 winding at about 220ma, this should be enough for the design I am looking for.

Are my calculations correct? or by joining the two 300-0 windings of 150ma, I would only get an extra winding of 300-0-300 at 150ma.

Thanks in advance for your help.

[Helmholtz]

What rectifier circuit and type are you going to use?

[Leadman]

Bridge Diode recitifer, with Capacitor Resistor smoothing:

100uf-220R-50uf-22k-22uf-15k-22uf

[Helmholtz]

With a bridge rectifier the output DC current is roughly 0.6 times the winding RMS current.

Two transformer windings can be paralled for doubled current, if
1) winding voltages are identical and
2) the voltages are in phase.
Maybe Dirk can give advice regarding the wire colors for parallel wiring.
Otherwise you will need some testing to determine relative phase.

[Volka]

Hello,

reading the description Voltage phase is obvious (to me) :  Sec 1: 0V green and 300V red . Sec 2 : 0V white and 300V blue.

Cheers and Merry X-Mas

Volka

[Helmholtz]

reading the description Voltage phase is obvious (to me) :  Sec 1: 0V green and 300V red . Sec 2 : 0V white and 300V blue.

That's not clear enough.
Voltages at red and blue wires could still be opposite phase with green and white wires connected.

[Dirk]

Hallo,

grün weiß und rot blau zusammen für parallele Verschaltung.

Gruß, Dirk

[Helmholtz]

So, according to Dirk, green wire to white wire and red wire to blue wire for paralleling the windings.
This will allow for a DC current of 180mA.

[Volka]

 

[Helmholtz]

I've seen cases where a transformer manufacturer mixed up wire colors.
For that reason, with green and white wires connected I'd measure the voltage between the red and the blue wire before connecting them. Should read 0 VAC.
When paralleling out-of-phase windings, something will blow (hopefully only the mains fuse).

[Leadman]

Thank you very much for the answers.
Considering 180 milliamps in the secondary high voltage winding, in theory there should be more than enough to feed the proposed circuit.

Kind regards.

[Leadman]

Thinking about it, I think it would be better to connect the power transformer in series and with a center tap.
Would that give me more current available in the secondary HT circuit?

[Helmholtz]

Would that give me more current available in the secondary HT circuit?

Sorry, no.
With center tapped 2-way rectification there's no current doubling and available DC current is around 0.9 times the AC current limit, so only 135mA.