Tubelab SSE B+ calculation - diyAudio
 Tubelab SSE B+ calculation
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 26th February 2014, 02:47 AM #1 diyAudio Member   Join Date: Feb 2009 Tubelab SSE B+ calculation Hi, and sorry in advance if this should be easy to figure out... building an SSE, I see and understand the tables for cathode bias resistor, but cannot calculate B+. Plan on installing the FREDs and SS/tube switch but am most interested in calculating for a tube rectifier. I saw another thread where someone recommended downloading and running a simulation with PSUD2; I did that and the number (B+= 326V) seemed too low. Rectifier: 5AR4 Power Supply: EDCOR XPWR002, 360-0-360 Choke: Triad C-14X = 6H; Cur 200mA; DCR 150 Ohms 100uf Motor Run Cap 5K OPT (GSXE Edcors) I plan to install binding posts to install different cathode resistors for different tubes, but need to know the B+ to get started with KT88s. Thanks in advance for the help.
 28th February 2014, 02:03 PM #2 diyAudio Member     Join Date: Jan 2008 Location: So.Cal. Can you post an image of your PSUDII sim?
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sim

here's what I got with a 10H choke
Attached Images
 SSE_5AR4.jpg (122.2 KB, 255 views)

 1st March 2014, 12:50 PM #4 diyAudio Member     Join Date: Jul 2005 Location: West Virginia panhandle You are missing the first cap. There should be a capacitor from the cathode of the 5AR4 to ground. It should be between 33 and 47 uf and it's value will determine the B+ voltage. I haven't tried the Edcor transformer, but measured B+ with a 360-0-360 volt transformer from an old HP oscillator gives 420 volts with the 5AR4 and 450 volts with solid state diodes in an SSE with 6L6GC's. __________________ Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
 3rd March 2014, 01:02 AM #5 diyAudio Member   Join Date: Feb 2009 Thank you for the help!
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I have attached a snap shot of the power supply you'll end up with, based on your existing Edcor transformer. The 5ar4 is a full wave rectifier, meaning that there are 2 sections inside the glass envelope. The Edcor you're using is a center tapped transformer so the power supply will be a "full wave center tapped" type as shown on the attached schem. Your attached schematic is that of a half wave rectifier supply. PSUD shows two tubes but these are really the two separate sections of the single rectifier. Since Edcor doesn't provide No Load Voltage or DCR specs, I had to make some assumptions and these are inline with a transformer of this size, voltage and ampage capacity.

You will also notice that I used a constant current load of 140mA instead of the 5K resistive load. The 5K resistive only draws ~90mA in this configuration. If you bias your output tube at say 60mA (based on your choice of cathode resistor) and allow another 10mA for the driver/CCS stage, that's a total of 140mA for both channels. These PSUD sim results are very close to George's actual measured results above and I'm pretty sure that he isn't running the finals at "only" 60mA. One more thing to keep in mind is that your line voltage will probably be closer to 125V so the numbers here will likely go up. If you can measure both primary and secondary DCR's as well as No Load Voltatge (simply connect primary to line and then measure voltage at secondary - carefully!!!) you could calculate with fairly good accuracy your actual B+ voltages.

PS. I zoomed in on the waveform in the simulation to show the voltage ripple, which at 60 mVolts is pretty decent. (77dB bellow main level)
Attached Images
 sse psud sim 3-3-14.JPG (106.1 KB, 204 views)

Last edited by musical noise; 4th March 2014 at 08:08 PM.

 5th March 2014, 08:27 PM #7 diyAudio Member   Join Date: Feb 2009 Musical Noise... thank you for running that sim! one thing I could not figure out was how to add the cap before the choke. I guess I'll poke around with it more but this is very helpful.

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