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Crate V18 with no PSU, got an idea
Crate V18 with no PSU, got an idea
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Old 11th August 2018, 07:40 PM   #1
Vincebus Riveruptum is offline Vincebus Riveruptum  Chile
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Crate V18 with no PSU, got an idea
Default Crate V18 with no PSU, got an idea

sup!, past weekend bought a Crate V18 guitar amp for dirt cheap, $30 (20.000 pesos chilenos), originally the owner brought me this amp to fix it, after some inspection noticed it hadnt a power supply at all, seems like someone removed it. The obvious solution is getting a new transformer, but its impossible for us, so instead of dumping it i asked him to buy it and he accepted instantly.


This amp has so much potential, also i've never had a 'serious' amp, what i could do? I thought about making a modding some transformer, but must be the cheapest possible. First I tried modding a MOT i had lying around and rewind it to get 350v, 6v and+- 12v however , just tried it today and god...that thing rattles just too much, also i read somewhere the construction of this kind of transformers is really not suitable for audio.


but what about modding an isolation transformer? they are not expensive at all, and the small ones seem good for this purpose(100 w or less)? The laminations are ok, power rating, everything sound fine to me, the only job is rewinding the secondary, what do you think about it?
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Old 12th August 2018, 04:42 AM   #2
thoglette is offline thoglette  Australia
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Quote:
Originally Posted by Vincebus Riveruptum View Post
The obvious solution is getting a new transformer, but its impossible for us, so instead of dumping it i asked him to buy it and he accepted instantly.
OK, down here in the antipodes power supply and output transformers are bloody expensive and there's a history of work arounds.

In short, for B+ one can use:
a) back to back transformers. Works as long as your B+ isn't too high or pulling too much power
b) voltage multipliers. Take 30VAC or better and cascade your way to B+

There's no rule that says you need to pull heater from the same iron as the B+ either. Use multiple bits of iron to get the voltages you need.

A particularly clever example is GC Will's SOLO but also look at his Lamington 15W- it'll be very close to what you need for 18W

The images below are his.
Click the image to open in full size.
Click the image to open in full size.
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Old 12th August 2018, 06:05 AM   #3
Enzo is offline Enzo  United States
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So the original SMPS made +320v, +6.3v, and +/-17v.
SO you need a transformer making about 225vAC, plus the heaters, and if not the same transformer, at least one that will make a pair of 15v supplies.

How about Fender, can you get Fender iron? A Blues Junior ought to be close.
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Old 12th August 2018, 02:43 PM   #4
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Shame really as R120 mainly goes high value not allowing the power supply start up.
A secondary diode can go short circuit causing the power supply to trip but they are generally quite reliable.
The +-17v supplies are actually +-15v. Not critical.
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Old 12th August 2018, 04:52 PM   #5
Vincebus Riveruptum is offline Vincebus Riveruptum  Chile
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Crate V18 with no PSU, got an idea
Quote:
Originally Posted by Enzo View Post
So the original SMPS made +320v, +6.3v, and +/-17v.
SO you need a transformer making about 225vAC, plus the heaters, and if not the same transformer, at least one that will make a pair of 15v supplies.

How about Fender, can you get Fender iron? A Blues Junior ought to be close.
Maybe but that would be expensive, fender chile goes nuts for prices
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Old 12th August 2018, 05:06 PM   #6
Vincebus Riveruptum is offline Vincebus Riveruptum  Chile
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Crate V18 with no PSU, got an idea
Hey thanks for the reply guys, thoglette i think i'd go for a) because i already got a transforner, yesterday bought an 220v/110v transformer for cheap so i just take it a rewind it, my only issue is my little experience on this matter and the small gap beetwen the core an the bobbin, that space seems so small for a secondary over it. Gotta show you some pics
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Old 12th August 2018, 08:00 PM   #7
Vincebus Riveruptum is offline Vincebus Riveruptum  Chile
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Crate V18 with no PSU, got an idea
some photos of the transformer, kinda feel bad for it because its vintage and good quality, he will serve for a great cause.


as you can see it has too much cardboard in between, taking a lot of space. I have to build it again with less carboard.


1T.jpg

2T.JPG

3T.JPG

4T.JPG

5T.JPG

6T.JPG

7T.JPG
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Old 13th August 2018, 10:53 PM   #8
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by Vincebus Riveruptum View Post
...I already got a transforner, yesterday bought an 220v/110v transformer
Chile has 220V AC mains, yes? If you plug the 220 V side into the wall outlet, and use a voltage doubler (two silicon diodes and two filter caps) on the 110 V secondary, you will get somewhere between 330V - 360V DC.

That may be a little less than the original power supply voltage, but it should make enough power from the amp to have fun with.

As for the other lower voltages - why not look for second-hand switch-mode DC power supplies? I'm not sure what these cost in Chile, but if you can find an affordable one with a voltage a little more than 6 volts, and a big enough current rating, you can run the heaters from it. Just insert a suitable power resistor in series to drop the voltage a little, so you have 6.3V at the valve heaters.

I use an 8.4 V, 1.8 amp, Sony power supply with a series resistor to run the heaters in one of my amps. The power supply was found in a thrift-store, and I think I paid $2 for it, because of the oddball voltage (nobody else wants an 8.4V supply.)

You can take the same approach for the +/- 15V or +/- 12V rails. For example, many Hewlett-Packard inkjet printers use a three-wire power supply that delivers 0V, +16V, and +32 V to the printer. When the printer fails, people throw away the power supply or give them to thrift stores. Around here, you can find them very cheap. Maybe in your area as well?

The DC output of these HP printer power supplies (at least, all the ones I've seen that have a two-pin AC mains plug) is completely isolated from the AC mains side. So, if you ground the +16V wire, you now have -16V, 0V, and +16V rails - perfect for op-amps!

I have used one of these in a home-made op-amp audio project, and with a little extra filtering on the +/- 16V rails (small series resistor and 100 uF electrolytic cap to ground), it works very well.

-Gnobuddy
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Old 14th August 2018, 12:06 AM   #9
Vincebus Riveruptum is offline Vincebus Riveruptum  Chile
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Crate V18 with no PSU, got an idea
Quote:
Originally Posted by Gnobuddy View Post
Chile has 220V AC mains, yes? If you plug the 220 V side into the wall outlet, and use a voltage doubler (two silicon diodes and two filter caps) on the 110 V secondary, you will get somewhere between 330V - 360V DC.

-Gnobuddy

Yes, here is 220v. I thought the same before i dissasembled the transformer, but the thing is actually an autotransformer, is not isolated. Just adding a multiplier would have been super easy...



Now i have other issues, i also dissasembled the primary thinking i could rewind it more compact, but the results werent the expected, i dont have tools for winding transformers so i was doing it by hand, I had to stop at half way beacuse the thing wasnt looking good as it was the size as the original.

Also it was difficult to coil because the bobbin had no edges, making harder to coil without wasting space.


Seems like i have to spend for a new primary with smaller gauge for more space and less power(it was originally 125-ish W) above 40 watt would be fine i guess.
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Old 14th August 2018, 06:49 AM   #10
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by Vincebus Riveruptum View Post
i also dissasembled the primary thinking i could rewind it more compact
I tried the same thing many years ago, when I was still a boy. I had no success either. I could not wind the coil as neatly by hand, nor stuff the laminations as tightly. And the sharp metal edges cut my fingers, so I left some blood behind in the (badly) wound transformer.

-Gnobuddy
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