Build Your Own Clone Message Board

As might know, I'm having some trouble with my 18W Baby Will build. The amp is build with the 2.3 Baby Will PCB from http://guitaramplifierpcbs.com/.

The issue is, that I'm blowing power transformers during the tubeless testing. I've turned two PT's into trash.
After the first PT went belly up, I re-did all my wiring, but the same thing happened. Sadly the second time, I once again forgot to use a light bulb to save parts.

I don't blow my 2A fuse, but the transformer is harmed.
When I power up the amp, for testing, there's a slight humming sound which gets slightly louder after a few sec., and then I notice the PT making a sound like water coming to a boil - and then comes the smoke and smell of something burned.

I live in Denmark where we use 230V, no ground/earth on the wall wart. I'm using the PT275.2I from http://www.musicalpowersupplies.com/


I've got a photo album with pics at http://www.photobucket.com/ptblowing18w - I can get more pics.
I've got the build guide, and wiring layout of the project on PDF, if anyone wants them.

A dying PT won't always blow the mains fuse, particularly is the problem is a low VA secondary that's shorting. It simply doesn't create enough current draw on primary side to blow the fuse. I roasted a 100w Peavey PT this way once. I shorted the 20-0-20 winding with a stupid wiring mistake.

I see you have the 5/6.3v heater winding wrapped, you could be getting a short in there.

Can you grab a clear picture of the back of your DP switch? I think I can tell what's going on, but being on the primary side, I'd rather be sure it's right than assume.

Have you tried firing up with the new PT with all of the secondaries just capped off? That would confirm your primary side wiring/parts are working properly.

I hope that's not the issue, cause all unused wires were tied down, and individually insulated with shrink wrap.




I'll get a pic ASAP.


The one that's in now is the fried PT. I just got the brand new PT yesterday, and I haven't gotten around to doing anything yet.

I must admit, I'm a bit scared of frying this third PT

Cool. And don't be scared, we'll step you through it and get it up and running. There are enough tricks out there we can nail this down pretty quickly.

When you pull the second PT, do some basic diagnostic testing on it to see if you can figure out the cause of death. This will give you a direction to look in for where the problem is. http://www.geofex.com/ampdbug/pwrtrans.htm

Great
Thanks for the link. I'll start testing when I get home from work.

More pics are up at http://photobucket.com/ptblowing18w named 1, 2, 3 and 4.

The Guitar Amp PCB site appears to be dead. I'm getting 404 errors from both internet links and your link; http://www.downforeveryoneorjustme.com/ says it's down too. Is this the schematic that matches your board? http://rh-tech.org/public/z_stingray_pcb_files/Baby_Will/.Baby%20Will%20v2.3%20Schematic%20v5.pdf

Assuming the schematic above is correct, you have too many diodes installed in your HV rectifier circuit - that is causing your HV winding to short every half cycle and cook the PT (this is the same mistake that killed the Peavey PT I mentioned above). Because this is a CT rectifier circuit, you only need the winding to B+ diodes, not the winding to ground diodes. According to the schematic, D3 and D4 should not be populated. I can't tell the diode number from here, but the outside two diodes are what look like they need to be removed.

Did you reduce the size of the fuse to accommodate your increased primary voltage? If you didn't reduce it to 1A, that might be why the fuse didn't blow.

I think the owners widow has shut down the site.
That is the right schematic, but now I'm confused. I followed the PDF build guide, and it said to use all four diodes.
http://issuu.com/manicsubsidal/docs/baby_will This is the PDF guide.

Having too many diodes, shorts the power to ground, so the risk of components damage on the PCB is minimal, right?

I used a 2A fuse I'll see if I have any 1A fuses in stock.

IIRC, the 4 diodes are if you're re-using the valve jr. tranny. Otherwise you use 2.

^Correct. That guide is for converting a VJ to a Baby Will, not for building a Baby Will from scratch. Since you supplied your own transformers, that part of the build document isn't applicable to you. Before you try this again on PT 3, compare the build doc to the schematic and see if there are any other discrepancies. I don't think there would be, but it's probably worth a look.

The rest of the parts will be fine. The two diodes you remove might be damaged from over current; I'd toss them.

Just a quick update.

I didn't have the fuses, so I've had to order them. The fuses hasn't been shipped yet, so I can't really do much atm.

YEEEEEHHAAAWW

I finally got my fuses yesterday. I hooked up the amp to day, and now it's making noise!!!


Thanks guy! Pulling the two diodes did the trick.
Now I'll just install the VVR, fix up the amp cabinet and speaker cabinet, and then I can cross this build off my list

Good deal! Make sure to properly heat sink the MOSFET in the VVR circuit. That baby will get super hot and needs all the love it can get.

Will do

I've seen Peavey amps, that had electric fans in them, to keep them cool. Would it make sense to have one in the Baby Will?

Fan va kul att du fixa den, whohoo!

I have no idea why Kfuz yelled at you but congrats man!

It won't hurt, but it's probably not necessary unless you have really restricted air flow in the cabinet you're building.

Tak, det synes jeg også. Den forstærker tog alt for lang tid at bygge




Swedes are a loud and noisy people. We just gotta deal with it
Thanks!








Well, I was planning on using a lot of perforated sheet metal, for the chassis... So I'll wait and see how things turn out.

Very happy to see you got this nagging issue resolved! CONGRATS!!

BTW, you may want to consider editing the thread title in your first post to indicate that the problem is fixed. Just a thought....

Thanks
Good idea! I didn't think about that

Post pictures and soundclips!!

I'll see if I can get that done, when I've finished up the cabinet