Got the regulator in and all is working well :dbtu: Thanks all for the help

Quote from: J M Fahey on January 06, 2015, 10:04:03 AM
What for?
"2) the regulator itself might be bad

3) there might be a short in the +15V line which pulls voltage down and kills the regulator.

As Enzo once said, shorted Op Amps generally short + to -, meaning they equally compromise both sides, but in a few cases they might short to ground.

With amp off and suspect regulator removed, measure continuity/resistance from the suspect +15V rail to ground.

Use various scales, at least the 2k one, the 200r one and the diode test one, both ways."

Since it was out of the board just to check and see if the regulator was actually bad or not. I know it doesn't rule out that there may be a problem further on that caused it to be non functional and will continue checking per your instructions.

Thanks for the reminder Roly. I actually ran my + lead through a 30amp discharge board I made to condition my battery packs. Regulator is bad. It is my understanding that these regulators are pretty trouble free so now will run some test (thanks for the direction FM) to see if it was just a bad regulator or if there is a problem somewhere in the preamp section that caused it to go bad.

Thanks for the reply galaxiex. I am kind of stuck with them as I already ordered them. Something I gleened from another site on these:

"Hi, i have some experience with the Jan6418 tubes - i've designed a few circuits around them now....

Firstly the Oatley kits set the impedance way to low at around 200k - i have tried 2 kits prior to designing my own...

Setting impedance at 1Meg solves the issue of microphony - i currently have my new preamp exposed with tubes just in grommets with none of the high pitched ringing associated with the oatley kits.... with my speakers up quite loud

Also for the tubes to work as per the datasheet impedance needs to be at 1Meg as eg... optimal plate voltage is at around 18-22v (for maximum gain - with 1Meg resistors)... setting impedance at around 200k or lower lowers the maximum gain voltage to around 14 or less - this also produces the unpleasant ringing even at normal listening levels...

I made the mistake of assuming the Oately designs were right and initially desiged a preamp around their circuit - it rang even in a solid metal enclosure..."

So now the question is how to set the impedance to1Meg?

I'm multi tasking here :loco while trying to fix one amp I am building another. I mean if I built my guitar why not build my own amp.

DISCLAIMER:KEEP IN MIND I'M A NOOB TO GUITAR AMP CIRCUTS.

I can understand and follow schematics, know transistor values, know what most of the parts are and the basics of what they do and my soldering skills are decent. I am in the process of building a LM3886 mono amp from Chipamp.com

I have ordered these two kits and was wondering if anyone has any experience with either of these pre-amps?

http://secure.oatleyelectronics.com/files/K261notes.pdf
http://secure.oatleyelectronics.com/files/K270notes.pdf

Anyway here is the thought process of what I'm thinking of doing.
Guitar > k261 preamp > gain > k270 preamp > volume > LM3886 amp.
My theory is to use the k261 like a gain channel. I have a transformer from a powered speaker (9 volt 1 amp) that I can power both preamps with by changing a couple resistors on the k261. Is this a do-able setup? Or am I setting myself up for failure?

Thanks guys,  It is getting 22.4 volts at the input if my memory serves me correctly. I have pulled the regulator out of the board and will throw a couple rc battery packs in series for 24 volt input and check it to see if it's  good or toast. Then will go from there.

I have attached a pic of where I think the problem is. I believe the voltage regulator on the left in the photo is bad. By following the etches on the board and checking voltage I am getting a -15.4 voltage out of the one on the right, the one on the left I am getting various +mv readings. Am I on the right track?

I pulled this out it is a L7815cv

Thanks for the info guys, no there is not any effects loop g1. Yes there are at least 4 IC's on the pre-amp boards. Can't really see if there are any on the chorus main board or not yet.
I understand we are flying blind here, with an amp that is most likley considered a throw away amp, but I am working on it to get a better understanding of how all these things relate and work together. Being it is an accoustic amp I figure it might be a good setup for my 3String Cigar Box Guitar.
The shop I got it at is closing it's doors the first of the year and walked off with this amp plus a Fender Frontman 25R that had a couple scratchy pots that I replaced and is working fine and the head from a  Peavey 240t Deuce that had been dropped off a truck and had the front damaged breaking three pots and two of the tubes. Got the front panel on it straightened out and the pots replaced just waiting on the tubes.
At any rate I think we are narrowing down the problem on this one. I am getting no power to the preamp boards so will have to figure out where the voltage is broken down.

Thanks for clearing that up for me g1. No continuity on the positive lead to the speaker. Voltage between leads to the speaker about 38 millivolts. Rail voltage on amp board +/- 40.3 volts. Kind of running blind here, have no schematics. Talked to Eleca and they said they might be able to dig one out for me but may take a while as the amp is discontinued. Meanwhile what might the typical voltage going to the preamp boards?

Got the transistor wired back in. I think I read/heard somewhere I shouldn't have continuity between either speaker lead to chassis ground. Is this correct??

Thanks for the welcome DrGonz78.  It does look like I snipped the PCB off. Yes I was doing a visual inspection and putting some slight pressure on the different components to make sure the solder joints were tight and the PCB just snapped right off. Looks like they used a little too much heat when they did the solder there and didn't seat the legs all the way in to the thicker part of the legs. The plugin on the board is a one way plug and the etching is a straight shot to each lead so doing them one at a time should keep them at the right connecton.

My appoligy for the double spacing in my first post, I copied and posted from notepad and having to leave for work I didn't have time to go back and fix it.

I'm new to the forum and a big hello to you all.

A short background on myself. I have  very basic knowledge of electronics

(I know what most of the parts in an amp are called and can determine

most values) Spent some time doing rework/repairs on circut boards for a

computer firm replacing bad chips, resistors, rewirering for updates and

fixing broken etches. So at least remove and replace are not a problem

for me. Where my problems start is that the boards I worked on came from

the techs with little orange stickers that said what needed to be

replaced or fixed. So I have zero diagnostic experience and my eyes and a

good multimeter for diagnostic tools.

With all that said: I have an Eleca EAA 60 amp that was said to be brand

new but never worked. The customer was given a replacement and it was

given to me by the guitar shop I deal with. What I have done so far is to

plug in the amp and a guitar and turned on the amp. The power light comes

on and I get a small speaker pop but no sound. So I have removed the amp

head and did some visual inspection. While poking around in there I

noticed the one etched board connected to the A1695 power transistor was

loose and actually came off with little movement.The board is just a

direct etch from wire to transistor. Can I just resolder the wires direct

or is the board there to keep the wires away from the heat generated?

I'm almost positive this is unrelated to the original problem. So my main

question would be where to start? I had thought about either plugging a

cd headphone outlet into one of the inputs and working my way down the

preamp board and seeing if I see signal or just running continuity from

the input lead down the board and seeing if there is a break somewhere.

At any rate where would you start?
Thanks in advance.