
Home  Forums  Rules  Articles  The diyAudio Store  Gallery  Blogs  Register  Donations  FAQ  Calendar  Search  Today's Posts  Mark Forums Read  Search 
Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum 

Please consider donating to help us continue to serve you.
Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving 

Thread Tools  Search this Thread 
1st January 2014, 05:50 PM  #1 
diyAudio Member
Join Date: Sep 2010

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 
1st January 2014, 06:22 PM  #2 
diyAudio Member
Join Date: Sep 2004
Location: Budapest

"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. 
1st January 2014, 06:24 PM  #3 
diyAudio Member
Join Date: May 2005
Location: Dallas (but I am not a Texan!)

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 
1st January 2014, 07:25 PM  #4  
diyAudio Member
Join Date: Sep 2010

Quote:
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 

1st January 2014, 07:28 PM  #5  
diyAudio Member
Join Date: Sep 2010

Quote:
The Valve Wizard 

1st January 2014, 07:40 PM  #6  
diyAudio Member
Join Date: May 2005
Location: Dallas (but I am not a Texan!)

Quote:


1st January 2014, 08:09 PM  #7 
diyAudio Member
Join Date: Sep 2010

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 
Thread Tools  Search this Thread 


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
5AR4 @ 250mA  scott17  Tubes / Valves  24  26th February 2012 07:06 PM 
Richardson 5ar4  Davec113  Tubes / Valves  13  4th August 2009 03:46 AM 
bad 5ar4?  sturmj  Tubes / Valves  2  11th February 2009 07:09 PM 
Got 5AR4 For Sale?  john65b  Swap Meet  0  3rd April 2008 07:59 PM 
New To Site?  Need Help? 