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Audio note kit 1 power transformer

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yashka

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Joined 2014
#1
I'm looking to built an AN Kit1 clone and have a nice Hashimoto PT-220F transformer that I want to use.
The only problem it has 380v (not 425v), what king of problems would i run in to by having a lower voltage?
3x 5V 3A each(not 7.5v) i don't think it's a big problem, i'll still use dc w/o a voltage regulator at the end. Please let me know if you have any other recommendations.
6.3v (just 1) i'll have all 6.3 heaters on the same transformer output. it should be powerful enough 2.5A.
thank you for your help.
 
#2
It all depends what looses you will have in transformer and current capacity .The resulting output voltage will be depended on the voltage sag under load .Kit one B+ is only 415V and it should be perfectly achievable with 380V transformer. You may have a situation when it will be actually ~440-460V . Measure the transformer and plug into Duncan amps PSUd II simulator .
 
#3
All Audio Note Kit 1 schematic(s) I found shows 435V B+. You may achieve it using a different rectifier (e.g., 5AR4) instead of 5U4G and modifying the power supply board (e.g., reducing the value of the bleeding or shunt resistor(s), increasing the capacitance of the second cap after the choke etc), as suggested try Duncan power supply design tool to approximate and fine tune after building the power supply. What is the power rating of the transformer? Most Canadian kits came with a big Hammond transformer #300XXXXX. Hammond makes a 850 VAC (CT) transformer @300ma that might work but you need a separate transformer for 300B heaters. I would try a transformer closer to original specs to avoid unexpected problems. A close one is Hammond 300BX rated at 800 VAC at around 290ma which might work perfectly with a 5AR4 without changing the power supply values much.
 
#4
Forward drop losses are what have to eliminated. The lowest losses will be realized if you rectify the B+ with high PIV Schottky diodes. Cree's C4D05120A is more than adequate for this job. Turn on surges can be tamed by installing a CL-130 inrush current limiting thermistor between the rectifying diodes and the 1st filter capacitor.

Schottky diodes are every bit as quiet as vacuum rectifiers. The "grit" parts should never fail, as long as care is exercised.
 
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