Push-Pull Voltage Regulator Amplifier transformer T2

Glenndk wrote:

Admin wrote:Hi Russ,
...
You want to drive a 50 Ohm load, so T2 impedance ratio is 14:50, or about 1:4.
...
BR Harry - SM0VPO - EA/SM0VPO

Sholdn't it be sqrt(50/14) or about sqrt(4) ?

Hi Glen,
 yes you are quite correct.

2+2 turns and 8 turns.

This is a 68-year old brain I am workin with ;-)

BR Harry

Admin wrote:Hi Russ,
...
You want to drive a 50 Ohm load, so T2 impedance ratio is 14:50, or about 1:4.
...
BR Harry - SM0VPO - EA/SM0VPO

Sholdn't it be sqrt(50/14) or about sqrt(4) ?

Hi Russ,
Sorry for the late response.

If I assume 100% output, the RF voltage is 8V at 600mA = 5 Watts
Impedance = 14 Ohms.

You want to drive a 50 Ohm load, so T2 impedance ratio is 14:50, or about 1:4.

The actual number of turns is not so critical as there is a useable frequency range of about 30:1. Too many turns and the inter-turn capacitance is a problem (at 30MHz). Too few turns and the coil does not have enough indictance to have a high impedance at low frequencies.

Using a medium ferrite with two holes, use 2+2 turns for the primary and 16 turns for the secondary. This sould be perfect for about 3MHz to 30MHz. If you need lower frequencies (top band?), then use 4+4 and 32 turns, and let me know what time/date you are on the band.

BR Harry - SM0VPO - EA/SM0VPO

Thanks Ivan,

    I am seeking to get a rough estimate of the number of turns of wire to
start with for the primary of T2. Just a ballpark figure.

Best regards,
Russ

Hi Russ,
"The circuit can be used for audio or radio frequencies." If you intend to use it for AF only, ferrite cores for AF with big mju are a good solution. The number of turns will decrease significantly.
I recommend you "the cheap ferrite rings from computer power units (about 2cm Dia.)" as mentioned in the 2,5 W version. One piece will be enough for less power.

BR from Ivan

The suggestions for T2 (audio) involve using a mains transformer.
My questions are:
    Would it be practical to wind T2 on a ferrite core for audio frequencies, or would
    that involve an excessive number of turns?
    If not impracticable, what would be a reasonable number of turns to try with for the primary?

Best regards,
Russ