• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Power transformer impedance

Hi,
I am going to use a 6X5GT tube rectifier in my power supply.
From the data sheets it needs at least 150ohms of limiting resistance on each plate (for capacitor input).

By measuring the power transformer I get
- 18 ohms across primaries (100V) whilst shorting a secondary
- 275 ohms across secondary (320 to CT) whilst shorting primary

So I think I have Rt=Rs + (n^2)*Rp
=275 + (3.2 ^ 2) * 18
= 454 ohms on each plate.
(PSUDII gives the same result).

So I don't believe I need to add any additional resistors.

Does this calculation look correct?

Does my measurement of the secondary look correct?
(it didn't seem to change whether I shorted the primary or not).

Thanks!
Jeff