Power transformer impedance

[hirafu_boarder]

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

 

[Tom Bavis]

Yes, you're correct. Inductance is reduced by shorting primary, but resistance is not.

 

[hirafu_boarder]

Thanks for the confirmation Tom!