Power transformer impedance

hirafu_boarder · 27th March 2008, 01:22 PM

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 · 27th March 2008, 01:50 PM

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

hirafu_boarder · 28th March 2008, 08:23 AM

Thanks for the confirmation Tom!

27th March 2008, 01:22 PM	#1
hirafu_boarder diyAudio Member Join Date: Apr 2007	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

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27th March 2008, 01:50 PM	#2
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	Yes, you're correct. Inductance is reduced by shorting primary, but resistance is not.

28th March 2008, 08:23 AM	#3
hirafu_boarder diyAudio Member Join Date: Apr 2007	Thanks for the confirmation Tom!

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