Did i model this PT correctly(psud2)? - diyAudio
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Old 16th February 2012, 07:10 PM   #1
ryuji is offline ryuji  United States
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Join Date: Feb 2011
Location: massachusetts
Default Did i model this PT correctly(psud2)?

seems like psud2 takes the secondary measured DCR plus the primary resistance times the square of the turns ratio, and you use the zero load voltage of the secondary as your starting point. that should model the transformer sag pretty reliably right?

i used ratio of 260/280 to estimate secondary resistance and unloaded voltage and my by hand math seems to match up with the 'calculator'

so my math is as follows:
0.928*292=271, thats my voltage
line side impedance doesnt change, thats 22 ohms
output impedance = 0.928*156=144 ohms
(260/120)^2=4.694 times 22 = 103 ohms plus 144 ohms = 247 which matches up pretty close to what psud2's calculator did

just wanted a second opinion before i go and potentially waste my money on a PT that isnt going to work. I expect the amp to consume between 40 and 50 mA of b+. im fishing for 300v obviously

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heres a hint of what im up to: cant really read it but thats 80 uF
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Old 16th February 2012, 07:34 PM   #2
ryuji is offline ryuji  United States
diyAudio Member
Join Date: Feb 2011
Location: massachusetts
i just noticed an error, that transformer isnt CT on the b+ secondary, opps. does my math work however for purpose of searching for proper one?

seems like both methods in psud2 come up with different numbers. guess when you dont have data on the resistance you can go by the regulation method using unloaded voltage but its not as accurate?

Last edited by ryuji; 16th February 2012 at 07:52 PM.
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Old 17th February 2012, 01:04 AM   #3
ryuji is offline ryuji  United States
diyAudio Member
Join Date: Feb 2011
Location: massachusetts
After getting somewhat frustrated with finding a transformer that would give me the voltage i was aiming for that didnt either cost a fortune or under/overshoot, i tried something that might be crazy concept wise.
Rebuilding my main amplifier with a new chassis is already on the planning book, making it more space efficient is quite easy to do as i have fewer parts then before. I could physically fit the aikido pcb and parts in the amplifier which gave me a idea:
i have a regulated ~300v supply already in my main amp, so why not relay the heaters on the big amp and aikido such that i would shut off one and turn on the other and run the aikido off the screen supply, the results are quite promising on paper. The transition should be smooth as there will be a 'cooling down' of the tubes and 'warming up' of the aikido, so I believe my 500v rated filter caps are marginally safe. guess i ought to setup the relay to also put a 10~20 mA load on the main b+ to keep it from going over 500
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The numbers near-perfectly match measured values for the big amp so i assume my rectifier and transformer models are accurate. The 1 uF is only there to keep PSUD2 happy, i use three OC3 regulator tubes

Last edited by ryuji; 17th February 2012 at 01:18 AM.
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