I acquired a Yamaha yg15 amp. The power transformer is toast. I'm looking for a schematic for it. I've been all over the internet without any luck. What I'm mainly looking for is the output  voltage on the rectifier circuit. Thinking about battery operated.

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Talk about a stroke of luck, on a whim I contacted a music store that did repairs to see if they had a schematic for this amp. It turned out last week one came in to be looked at. Apparently it was worked over pretty good because the circuit was smoked but the speaker and transformer are good( I question the speaker because that horse was ridden hard) anyway they're mine for the price of fuel to pick them up! Problem solved! A complete amp for free, just the way I like it. For shots and giggles I'll post the voltage out. For inquiring minds. Thanks everyone!

Glad it worked out for you in that way. At least we learned something along the way.

LOL yes I did, "it's in the trash for a reason"! Thanks for your support. I'm going to pick up the other piece of junk today and go from there!

awesome. seems like a nice chip the TDA2030. there are quite a few TDA chips used in amps... 

on a side note i would almost bet that the amp board in your amp is the same circuit that is in the data sheet.  common practice to use the suggested circuit from the datasheet.

As close as I can tell it is the same circuit. BTW the transformer is spitting out 34 vac. I don't know if my meter is off (harbor freight freebie) or if the dc voltage is 24 v, imo 10 v is a big drop through a rectifier circuit.

34V ac fully rectified is 48VDC peak. filtered will probably come down to 44V DC.  +- 22V DC is the max for the amp. so maybe its right? 

Shows how rusty I am, I forgot about the filtered voltage drop. It's been a million years since I used any practical electronics outside of resetting the receiver and changing fuses.

You can get these chips new from Mouser.com and Smallbear.com if you need any for repair or building your own circuits.

I'm thinking about  buying a circuit board with the chip in it and modify it to use in in the second housing. The repaired amp sound great. Thanks for the info.

hi Guys while the folks into amps are gathered here, here is a list of the amp manufacturers who's circuit diagrams I have, just in case any of you are interested at any time.

There must be 80 diagrams for different models pre 1975 for the following brands

 Epiphone - Estey - Gibson - Harmony - Kay - Supro - Sears Silvertone - Wards Airline - Ampeg - Valco.

Glad you got it sorted Will.

Taff

This sucker rocks! One of my neighbors has a Cube and he did a side by side comparison by wringing them out with the same song/settings(as close as possible). You'd be hard pressed to distinguish between the two. What the hell for free I'll take it! Man! You've gots some oldies there, my brother back in the day had a "Monkey Wards" I don't know if my nephew still has it and the lap steel, I had forgotten all about it until I saw your list. Thanks for the walk down memory lane. I might be taking you up on that offer. Thanks!

Glad you got it working.

I also have a lot of tube amp schematics - Fender, Gibson, Marshall, Valco, Silvertone and Ampeg.

On a side note: First Act has a little 4watt and 10watt guitar amp that most folks pawn because they sound so bad. I found one on the curbside and it did sound bad. The source of the bad sound? Cheap small speaker. I added a Jenson Mod speaker and the Bassman mod(Higher value input cap) on a switch and that little amp Rocks.

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