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Old 1st January 2014, 05:50 PM   #1
MFF is offline MFF  Portugal
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Default 5AR4 PSU

hello guys,

I am designing a power supply for an amplifier, but I have some doubts about the calculation for Minimum Limiting Resistance (RLIM (min))

Rt= Rs + (n^2)* Rp
Where:
Rs = DC resistance of one half of the transformer secondary winding.)
Rp = DC resistance of the transformer primary winding.
n = Secondary to primary turns ratio (equal to the secondary voltage divided by the primary supply voltage).

Can someone please confirm, if my calculations are correct, in this configuration I have 250V per plate right?

The limiting resistor per plate at 300V is 75 ohms, by my calculation I have 133 ohms therefore no need to place a resistor. Assuming my calculation is correct.

Please see files in attach.

Thank you guys for the help

MFF
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File Type: pdf EDB370KX.pdf (371.6 KB, 15 views)
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Old 1st January 2014, 06:22 PM   #2
euro21 is offline euro21  Hungary
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"Rs = DC resistance of one half of the transformer secondary winding."
Why "one half"?
HV secondary is 250V+250V= 500V AC, with 42.43R (correct?) DCR.
Without SS diodes this is the half wave rectifier.
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Old 1st January 2014, 06:24 PM   #3
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The secondary is a little confusing. Is it 2x 250V (500V total)?

If so... I think "N" is also per plate, not total, so should be 250/240...

Pete
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Old 1st January 2014, 07:25 PM   #4
MFF is offline MFF  Portugal
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Quote:
Originally Posted by pmillett View Post
The secondary is a little confusing. Is it 2x 250V (500V total)?

If so... I think "N" is also per plate, not total, so should be 250/240...

Pete
Hi Pete
Yes is a 2X 250V total of 500V
you're right is 250/240 so after recalculating we have TR= 21.2 + 1,08 x 5,2
RT= 26,8.

As we have 250V per plate and by the datasheet of the 5AR4 the minimum for 300V per plate is 75ohms so I need 75 - 26,8 = 48,2 ohms resistor I am, right?

Thanks for the help

MFF
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Old 1st January 2014, 07:28 PM   #5
MFF is offline MFF  Portugal
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Quote:
Originally Posted by euro21 View Post
"Rs = DC resistance of one half of the transformer secondary winding."
Why "one half"?
HV secondary is 250V+250V= 500V AC, with 42.43R (correct?) DCR.
Without SS diodes this is the half wave rectifier.
cheek this link
The Valve Wizard
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Old 1st January 2014, 07:40 PM   #6
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Quote:
Originally Posted by MFF View Post
Hi Pete
Yes is a 2X 250V total of 500V
you're right is 250/240 so after recalculating we have TR= 21.2 + 1,08 x 5,2
RT= 26,8.

As we have 250V per plate and by the datasheet of the 5AR4 the minimum for 300V per plate is 75ohms so I need 75 - 26,8 = 48,2 ohms resistor I am, right?

Thanks for the help

MFF
That seems about right. It will drop your B+ voltage a bit...
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Old 1st January 2014, 08:09 PM   #7
MFF is offline MFF  Portugal
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will be around 14V.

I am taking the high voltage B+ from the CT of the 5AR4
filaments winding, this way we have less noise from the 5AR4 filaments into the B+ . this is correct?

Thanks
MFF
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