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12 volt to 300 volt inverter question for tubes

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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.
 
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.
 
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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.
 
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.
 
I like the diagram there. That does look sufficient for my needs. I have a transformer apart now. I will rewind on it with proper wire. Also like the ebay item for $5. Some of you misunderstood me, so I will clarify. My project only needs about 1-watt of power, voltage can be from 100-300 volts Dc, preferably 300 volts, which I need to get from a 12 volt supply. The 12 volt supply is a computer power supply. The power inverter I would like like small enough to fit in the case. I am not using a 12 volt tube as of yet, so I confused you on that. I will use a 12 volt volt tube later. I am not looking for a lot of power output as I am only building a preamp. If I was two 12k5 tubes would give me 1 watt. The actual 12 volt tube I will be using is a 12B4. That is for my second project.

This project I am using a 12AX7 which needs about 1.2 Ma at 250 volts, somewhere around that anyway. I have a lot of parts to build things from scratch, so just looking for ideas and your diagrams. Even the ebay thing was a good idea. could save me a bit of time. I wonder sometimes about items like that though, just how stout it is and how long it will last. Since I will be making these for people I want it to last without fail. I could of course look it over and beef it up to my specs. The one on ebay could have a frequency not usable too, as it says it is just for phones and nothing else, makes you wonder. Anyhow I need to duplicate my project once its working properly. You know have to tweek on it for awhile, that's half the fun!
Oh the 2n3055 inverters are too much for what I need. I could probably get 100 watts out of those babies. I could use the same principle just use a smaller transistor. My forst thought was a 555 timer. After playing with it I realized I had to run it into a switching transistor to get it to drop to zero volts. I needed it to drop to zero in order to get a good rise and fall to get more voltage from transformer.Then I ran that to my mosfet as the load switching. I used an old tube radio 50c5 output transformer in reverse to get about 300 volts. But for some reason I couldn't get enough amperage out of it to do squat. Then I killed it somehow, even had protection diode on output, then all I could get was about 100 volts that dropped down to about 65. Haven't been out to the shop since to try it again. Reason why I came here to see what others dream up. Then I will take what I get here and go for it again. I love looking at all the ways possible. thanks for the replies.
 
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UC3843 is perfect for that, a flyback switcher is just what you want for low power. It will run quite nicely from 12V, and provide plenty of power for something like that. The Vadj pot will provide a factor of 2 adjustment, which was probably something like 150-300V in that schematic.

Only change I can think of, besides removing the heater winding if you don't need it (however, I would still suggest a 6.3VDC regulator, or a 12VDC LDO, for the heaters since automotive power is NOT generally within 10% of 12V), is potentially adding a 4.7k to 47k resistor in series with the leftmost 0.01uF capacitor (this is the feedback compensation capacitor). The purpose is simply to stabilize the supply against transients and preventing oscillation. Stability is easy to test if you have a digital oscilloscope, or a quick eye on a triggered analog scope -- just adjust it until, by repeatedly switching power to the circuit, the output voltage stabilizes the fastest with minimal overshoot.

Tim
 
Actually, you don't need the transformer, cause mains isolation is not an issue here.
A simple Boost Converter will do.
I did build one with a 555 timer and it does well (regulation is not perfect but simple, there is some 10% drift with temperature).
I also built one with a 3843, which delivers anything from 1mA to 150mA.
Other proposals from the net.
Add pot to adjust voltage. Adjust caps to select switching frequency (50kHz or so).
Inductors are small, don't use power transformer.
Here's a collection of circuits ...
 

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pwr converter

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.


Hi yourownfree,

here is a converter that I made for a battery operated guitar practice amp the other day. It run most every amp with 6V6 or EL84 , even an old valve radio will work with it.
The output regulation refer to the 6V heater voltage. I made two off this converters . They work with a good efficiency. A full charged 12V lead battery with 7,5 Ah keep the amp for 3,5 hr running.

regards

Wolfgang
DF6ZC

Here are the circuit diagram:
 

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Status
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