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Sainsmart transformer dead
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Old 11th October 2018, 08:52 AM   #1
Deafuser is offline Deafuser
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Default Sainsmart transformer dead

Hi all, I bought a cheapy chinese valve pre/buffer and it was running fine. I know its everyones favourite, but anyhow, I hadn't used it in a while and I purchased a nice case, amp board and PSU board and decided to install the pre. I did the assembly and fired it up! The valves glowed and audio crept forth and was just audible above the smell of burning varnish. I shut don't and finger tested for heat. Seems like my HT winding was cooking away nicely and I measured about 3 volts on the winding instead of 170 VAC!

My assumption is I shorted the capacitor tops to the lid of the case. I can find no other reason for failure. The board is no longer available, but the transformer is. For the price of the transformer, I could buy a different kit, which the holes cut in my lid may not line up. How can I rustle up 170 volts of ac to test my preamp?
Would I be scorned for using resistors in a potential divider? Just for several seconds to see if this board still works.

Thank you.
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Old 11th October 2018, 08:57 AM   #2
KatieandDad is offline KatieandDad  United Kingdom
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Have a look for an SMPS HV supply. Or build one. Don't try to go for 120 - 240V operation as the transformer maths becomes difficult. It's easy enough to get 170V from 12V.

Even a simple 555 driving a flip-flop will drive two transistors. Use a 15V / 240V transformer in reverse and you should get approximately 170V out. You can safely trim the voltage with CRCRC filtering. A small first cap will considerably drop the output voltage.

A Google search will reveal a whole host of circuit ideas using cheap components.
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Last edited by KatieandDad; 11th October 2018 at 09:06 AM.
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Old 11th October 2018, 09:12 AM   #3
Deafuser is offline Deafuser
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Thanks for the reply, I'm a single dad and my daughter is called Katy :-)

By time a circuits parts could be purchased and assembled, I could have a new transformer :-) But could be a learning curve! I'll give it a go, thank you KatieandDad

Can I use dc 6.3 volts to run the heaters instead of ac? Eliminal the transformer altogether. Thank you
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Old 11th October 2018, 12:35 PM   #4
KatieandDad is offline KatieandDad  United Kingdom
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You are welcome. I was just offering a solution for a cheap HV supply .
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Old 11th October 2018, 12:55 PM   #5
Deafuser is offline Deafuser
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Your help is greatfully appreciated, thank you ��
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