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Old 9th December 2011, 04:35 AM   #1
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Default 12 volt to 300 volt inverter question for tubes

My question is if you use a 12 volt dc source for an inverter that will be used for audio, using a tube, what frequency would be best? I am looking at either 60Hz or is it better to run it above the audio range. I will be making this myself as part of an audio project I am working on. I am pretty sure 400 Hz would be noticeable but the transformer effectiveness should be better. So I cant make a decision. What is your thoughts on this. It will be used for a guitar preamp. I know there are 12 volt tubes as I plan on using one in another project.
For this one I am using a 12ax7 tube. Even 100 volts would be ok, but I prefer a bit more voltage so I can switch it if need be as it is experimental. I am looking for an output of 300 volts but what frequency should I use for the inverter and just how efficient will it be. What circuit would work best using a switching circuit with a transformer or should I just use an inductor type boost? Of course any diagrams are always welcome. Always looking for new ideas.
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Old 9th December 2011, 05:10 AM   #2
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Here you go:

150W DC 12V to AC 220V USB Car Power Inverter Adapter | eBay

About 310V DC inside...
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Old 9th December 2011, 05:11 AM   #3
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dc is dc its how clean it is. higher frequencies require smaller caps to filter the dc, thats why planes are 400hz.
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Old 9th December 2011, 05:15 AM   #4
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Planes have 400 Hz because motors are much smaller. and lighter.
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Old 9th December 2011, 06:26 AM   #5
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150w would be overkill, all I need is 1 watt. As I understand it from the amateur radio handbook 400 Hz was more efficient and the transformer could be smaller for the same power. probably why 400 Hz was the standard back in the day. I guess even though the end result is DC there is still the input of the tube picking up stray electromagnetic waves even the 400 Hz, as I am sure shielding would be important to prevent this, but even so it has a way of getting through. Imagine instead of a slight 60 Hz hum you now hear 400Hz hum, not good. This is why I am thinking about raising the switching frequency above the audio range.

Last edited by yourownfree; 9th December 2011 at 06:32 AM.
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Old 9th December 2011, 12:45 PM   #6
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400Hz is used in a/c because the transformers are smaller and lighter. Its three phase as well. Are you thinking of making an oscillator at 400Hz and driving a step-up xformer or are u thinking a switching supply? Either way you wont get a tube running at 12volts to give u even one watt. You either need to use SS or higher voltage.
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Old 9th December 2011, 03:54 PM   #7
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Quote:
Originally Posted by yourownfree View Post
150w would be overkill, all I need is 1 watt.
Small cheap inverter that covers all your potential needs, what else do you want?
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Old 9th December 2011, 05:12 PM   #8
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I have an old 300W inverter that blew up it's output H-bridge stage (the part that chops the HV DC into something roughly resembling AC).
So I removed all of it,and stuck a voltage doubler on the output of the SMPS transformer (the 12V to 160V step-up part),and I seem to recall getting about 325V out of it,with more than enough current (couple hundred watts worth) to run a decent sized tube amp.
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Old 9th December 2011, 10:29 PM   #9
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Look for a 2N3055 inverter that uses a 120 (or 240) to 12.6V CT transformer in reverse. They should be all over the internet.
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Old 9th December 2011, 11:05 PM   #10
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