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Old 1st November 2019, 11:42 PM   #2111
mike567 is offline mike567  United States
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Please upload schematic to forum. Photobucket fuzzes them out!
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Old 2nd November 2019, 01:16 AM   #2112
Fenris is offline Fenris  United States
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Sorry about that, here's the schematic. Also a picture of the 12v to 230v PSU, the power supply filter, and the PCB.
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File Type: gif 6GV8_guitar.GIF (172.3 KB, 93 views)
File Type: jpg PCBs.jpg (770.0 KB, 80 views)
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Last edited by Fenris; 2nd November 2019 at 01:41 AM. Reason: added picture
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Old 2nd November 2019, 04:57 AM   #2113
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by Fenris View Post
Also a picture of the 12v to 230v PSU...
Nice project, and a handsome PCB!

Can you share any more info on the PSU? Using an SMPS instead of old-school 60-Hz iron used to only be an option for large corporations (Peavey, etc), but now it's starting to be viable for one-off DIY projects.

On another thread, someone shared this: High Voltage DC-DC 150V-420V Converter NIXIE & Tube HV Power Supply 1.25-12V adj 699904388163 | eBay

If the voltage ratings are to be believed, there's enough there to power any number of small "classic" guitar amps (push-pull 6V6, etc.) What doesn't seem to be too clear is how many watts this PSU can actually handle. The ad says "High voltage output current: 50-100mA adjust", which isn't terribly illuminating. Is that 50 mA at 420V (21 W)? Or is it only 100 mA at 150V (15 W)? Or something else entirely?


-Gnobuddy
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Old 2nd November 2019, 04:40 PM   #2114
Printer2 is offline Printer2  Canada
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My text seems to disappear. Let's try this. A cheaper version of the inverter can be found searching 'DC-DC 10-32V to 45-390V High Voltage Boost Converter Step-up Booster Module', won't take my link.


I have an amp project with the same architecture, of a dual triode with a Mosfet follower and splitter. I probably will do cathode biased on the output tubes though.

Last edited by Printer2; 2nd November 2019 at 04:47 PM.
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Old 2nd November 2019, 05:17 PM   #2115
Tubelab_com is offline Tubelab_com  United States
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The converter linked by Gnobuddy is a single ended boost converter based on an old TL494 chip. It's efficiency goes down as the difference between the input and output voltages go up. It is also a relatively low frequency device. The data sheet examples run at 10 and 20 KHz. I wouldn't expect more than a few mA st 300 volts or so before parts start to get hot.

The converter I see in pictures from Printer 2's description only has one power device, so it's probably single ended as well. It does use a transformer for step up, so it may do better in the higher voltage ranges.

I haven't tried either.

Many of the cheap inverters for powering small electronics in the car turn 12 volts DC into a high DC voltage, then chop it up into a quasi sine wave with a mosfet H bridge. I got some cheap ones made for European 240 volt 100 watt electronics on Amazon and tapped into the DC voltage inside. It's about 270 volts and good for 50+ watts of power continuously. As I found, they blow up if accidentally shorted. This was a few years ago and the devices I bought are no longer there, but I'm sure there are new ones.
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Old 2nd November 2019, 05:35 PM   #2116
Fenris is offline Fenris  United States
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If you search ebay for "DC-AC Converter 12V to 110V 220V AC 150W " you will find one like the one I'm using. It has a ST SG3525a PWM chip in it. It runs fixed frequency/duty cycle as far as I can tell. It outputs a square wave at 230v and I think 20KHz. Pretty easy to filter. You can even use a voltage doubler to get about 350v. The inverter transformer is probably good for at least 50w at 20KHz, 150w seems...optimistic. You can probably run it at 19v instead of 12v if you change the main capacitor to get 50% higher output voltage. They're cheap enough to run one for each channel.
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Old 2nd November 2019, 06:09 PM   #2117
Tubelab_com is offline Tubelab_com  United States
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An Ebay search with those terms reveals 4 different things. A square blue board, a square green board, and a long skinny rectangular board that looks like yours. It also brings up a red and black 12 volt to 220 volt car inverter.

The red and black car inverter looks like the one I got from Amazon. It took me 10 minutes to blow it up. I still have a silver Philips branded 70 watt inverter that I got from Amazon at the same time. It did a good job powering my laptop in the car, so I didn't rip it apart.

I suspect that the other three are the same design. I have the square blue version. It does have a ST branded SG3525 chip in a socket! It is a push pull design and capable of lighting up a 40 watt bulb without smoking. It produces an AC voltage so you must use your own rectifier and filter. Do not use ordinary 1N4007's, they start smoking in a minute with no load. UF4007's work fine. The board does not have any provisions for feedback, so the regulation sucks, but it's probably OK for a guitar amp. DC feedback could probably be added from the rectified output, but I never got that far.

Mine is still sitting a box trying to get my attention, but my ADHD powered brain wandered off in a different direction again. It's still alive though, I didn't manage to blow it up.
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File Type: jpg P3320727_x.jpg (621.3 KB, 67 views)
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Last edited by Tubelab_com; 2nd November 2019 at 06:13 PM.
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Old 2nd November 2019, 09:36 PM   #2118
Fenris is offline Fenris  United States
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The square blue board and the the skinny blue board are probably the same thing just in different form factor, right down to the same components and positioning of parts around the socketed SG3525. The square one might be a bit better - there are heatsinks on your board and mounting holes in the corners.

I use SiC diodes without problem. I tried running feedback and it didn't work, but it was probably because I found a cold solder joint or two on my feedback circuit after I took it apart. For a class-A or guitar amp it should work fine running all-out.
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Old 3rd November 2019, 02:21 AM   #2119
Fenris is offline Fenris  United States
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I got a chance tonight to take pictures of the first prototype I built. The primary difference with this one is that it runs at 230v, the preamp sections are regulated using a voltage divider/RC instead of zeners, and the output tubes are run as pentodes.

The cab is built with 3/4" pine and uses a piece of L shaped aluminum for the controls. The speaker is a Parts Express buyout 6.5" car speaker.
The back has a 80mm fan (Enermax Marathon, silent), a L-pad to reduce volume while keeping amp distortion, the 12v input jack, and a 1/4" jack wired to the second secondary winding to power either an external cab or as an output to a PA system (it's a little hot but works well with the input turned down).

The guitarist I gave it to says he really likes the sag and distortion at higher volumes, probably due to the pentode operation. He also likes the high gain of the amp so he doesn't need the gain of any of his effects boxes.

P.S. Sorry about the rotation of the photos, the forum software apparently doesn't like portrait orientation and rotates them.
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File Type: jpg combo_back1.jpg (654.8 KB, 52 views)
File Type: jpg combo_front1.jpg (665.7 KB, 50 views)
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Last edited by Fenris; 3rd November 2019 at 02:28 AM.
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