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Old 26th February 2014, 02:47 AM   #1
will98d is offline will98d  United States
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Default 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.
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Old 28th February 2014, 02:03 PM   #2
boywonder is offline boywonder  United States
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Can you post an image of your PSUDII sim?
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Old 1st March 2014, 03:45 AM   #3
will98d is offline will98d  United States
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Default sim

here's what I got with a 10H choke
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File Type: jpg SSE_5AR4.jpg (122.2 KB, 284 views)
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Old 1st March 2014, 12:50 PM   #4
Tubelab_com is offline Tubelab_com  United States
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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.
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Old 3rd March 2014, 01:02 AM   #5
will98d is offline will98d  United States
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Thank you for the help!
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Old 4th March 2014, 08:03 PM   #6
musical noise is offline musical noise  Switzerland
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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)
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File Type: jpg sse psud sim 3-3-14.JPG (106.1 KB, 229 views)

Last edited by musical noise; 4th March 2014 at 08:08 PM.
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Old 5th March 2014, 08:27 PM   #7
will98d is offline will98d  United States
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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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