| Electronics > Projects, Designs, and Technical Stuff |
| SMPS for vacuum tube power amplifiers.(status: back at it) |
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| SK_Caterpilar_SK:
Hello. I designed a switchmode PSU for tube amplifiers. The PSU is capable delivering upt to 70W of power and runs of 10 to 30VDC on the input. The output can be adjust to anywhere from 200V up to whatever your filtercap is rated for (450V). This was originally an idea of mine to switch out a really expensive transformer for the High voltage which would be nowhere near regulated and really heavy. The Powersupply has its advantages and its problems but those seem to be so far easy fixes. The big deal is, would anyone be even slightly interested in such a supply. I know that SMPS were frowned upon because of their noise, while my supply generates 0 audiable noise at the speakear even when looking at it with a scope. I originally intended it for my school project for a Tube amplifier. 20W RMS Mullard amplifier more specifically. Workse great no hiss nothing, I also posted the same question on a site called DIY Audio and one of the guys messaged me if it would be possible to power it with basically line voltages. My design has some problems and those would be fixed right away if working with line voltage, but I kept myself away from such a job because I simply dont feel comfortable enought to work arround line voltages. Its basically a Flyback converter that stepts the voltage up to 450V with a lot of power to back it up. Little bit bout me- Im a student and I just turned 17 last week and I basically consider myself as a home grade enginerd. Im into mostly analog stuff, high power regulators semiconductor amplifiers and many other things. Before you askt, the entire high voltage power supply was created by me. THere is no existing schematic for such a powerfull flyback converter from said input voltages to the said output voltages I wonder if it is worth it a all to continue the developement of the supply at all. Btw im not a native speaking so I apologise for any grammar mistakes I made. Thanks |
| Benta:
First, I applaud someone really enthusiastic about electronics at 17. Keep it up! About your current project, I have my doubts. Tube enthusiasts tend to be purists and like big transformers etc. I don't think you'll find customers in that area. |
| TimNJ:
Most "tube enthusiasts" are perfectly content in the year 1955. It's audio, so there's a lot of ~feelings~ involved, as we know. So, you're unlikely to have much appeal with that crowd. That said, an SMPS would allow you to cut down on size, weight, and maybe cost of a tube amplifier. Could be an interesting design challenge to see how small you can go. I'm not entirely sure how you deal with the output transformer, though. |
| SK_Caterpilar_SK:
--- Quote from: TimNJ on March 28, 2019, 10:37:41 pm ---Most "tube enthusiasts" are perfectly content in the year 1955. It's audio, so there's a lot of ~feelings~ involved, as we know. So, you're unlikely to have much appeal with that crowd. That said, an SMPS would allow you to cut down on size, weight, and maybe cost of a tube amplifier. Could be an interesting design challenge to see how small you can go. I'm not entirely sure how you deal with the output transformer, though. --- End quote --- The output transformer has to stay- its there to convert the tubes high impedance to low impedance that matches the speakers. Its a necessity BUT getting the power transformer out of the way it basically halfs the total weight of the amp with some advantages as of powering it from 12V batteries, cars, and more, also its tightly regulated and it has absolutely no noise whatsoever, and maybe even improved efficiency, but converting to 450V from 12VDC aint a an effective process. But I had a rather intresting requiest by one individual asking me to make a line voltage version. It would be much simpler in terms of managing losses and heat problems since more power but less current is involved. I had to use a IGBT for switching the transformer since a regular MOSFET has a body diode which creates unwated effects in the circuit. I know that people have feelings for the good ol transformers, and I dont blame them, go linear go quiet. But these days technology can achieve same, and the line being noisy aswell the transformers are not so different from my supply I designed. Im hoping to draw some more poeple into this, currently im recovering from the financial loss of making the tube amplifier itself and getting the HV PSU done. Once Im up again Im going to work further on the PSU. It will work of of proper mains rated from 90VAC to 265VAC with a power of abou 100W thats my goal to reach and up to 1kV of voltage. I dont have really the proper tes equipment for that except a old VTVM (vacuum tube voltmeter) I love dearly but the filament current source "barretor" seems to be not in the best shape at all. And it seems to soon require a simconductor fix. However it goes to 1kV full scale so no problems there. I just hope this project aint my last one xD. The 1kV output would be really catching for tube RF transmitters. I know the stigma arround anything else than true linear transformers, but at some point..someone has to come up with something that might be worth a shot. I could not find ANY comercial device that could provide this amounth of power or anything close. Not even an IC that do the work so I had to design my own SMPS controller based on the literature of MAXIM integrated and making the ctriangle gen and PWM gen and error amp so experimental purposes. As of now the GA3459 switching transformer is rated for 56kHz switching. The line voltage transformer could go even higher up to 100kHz would really improve noise basically eleminating even the electrical noise I can see with my old HP digital scope with a divider probe amd the fluctuation is about 1V pulses. Again nothing noticeable at that voltage. I also have a RLC filter there fo it does a real good job at filtering (10R series 470uH series and 100uF in paralel. The previous stge has only a 8uF filtercap after the diode and a very big fat 630V SMD cap biggest one I have ever seen in my life.). If anyone would be interest I could upload a video on youtube abou this. But the biggest problem im afraid of of the people to really hold onto those tranformers like even if my solution fits into 50 dollars and thats well within the manufacturing cost the engineering cost and the component cost. |
| SK_Caterpilar_SK:
--- Quote from: Benta on March 28, 2019, 09:51:54 pm ---First, I applaud someone really enthusiastic about electronics at 17. Keep it up! About your current project, I have my doubts. Tube enthusiasts tend to be purists and like big transformers etc. I don't think you'll find customers in that area. --- End quote --- Well hey thank you its been my passion ever since I was 8- from blowing stuff up into making making functional custom made products for special use and other things. I consider myself as a ENGINERD :D Yeah I have the same fear. Regardless I think people woul reconsider buying a 150 dollar transformer shipping not included or a 50 dollar same solution just lighter and not traditional as we could say. More versatile lighter maybe even more effective But I havent done math arround efficiency yet. I wanted to get it working for the competiton but it did not work out the way it was suposed to- the competition. You know how it works.. That one old guy saw me at the cross country competition this year totally crushing the school he brought hes students from and he probably made damn sure to not even let me compete xD. Ahwell screw competitions those aint bring money only pets my ego. But yeah it would have been the 6th competiton this year. Still got two more to go :D. About trannsformers- one would have to be left and thats the output transformer. It is necessary for a tube amplifier because vacujm tubes are high impedance devices- they cannot drive speakers directly like transistors. Tubes need a way of transforming high impedance to low impedance that matches the speakers there is the big fat output audio tranformer for. |
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