Repairing an lowery organ amp

[Trick Fall]

A few months ago I bought an old Lowery combo organ off ebay that is not functioning. This model has an integral amplifier which seems to be the problem. Right now the amp and keyboard power up, but only make a loud buzz/hum. I took a look at the umbilical connector from the amp to keyboard and noticed the ground cable had come undone. I rigged a test cable to ground it and was able to at least faintly hear the notes from the keys and the differences that the different tabs as well as the bass and volume pedals made so I am definitely thinking the problem is in the amp. Anyway i am pretty novice at this sort of work and was wondering if anyone could point me to instructions for safely discharging the caps as I am assuming this is the first thing I should replace. I am also thinking that I might have to replace the umbilical connector, but I don't know what this type of connector is called. Anyway any help is greatly appreciated.



This is a pic of the connector.

[???????]

that is a connector from an octal vacuum tube. They used to use them on organ cables sometimes. I think Hoffman sells 'em, or at least used to.

www.hoffmanamps.com

[???????]

yep, third item from the bottom:

http://www.hoffmanamps.com/MyStore/perl ... =535253173

[Trick Fall]

yep, third item from the bottom:

http://www.hoffmanamps.com/MyStore/perl ... =535253173

Thanks, I figured it was from a tube, but couldn't figure out what they would be called or where to get one.

[ckeene]

That amp looks pretty simple, which is good. It's also not vacuum tube, so it's less likely to kill you if you mess around with it. Regardless, BE SAFE when opening this up. Randall Aiken's site has some good tube amp safety tips that also largely apply to transistor amps, too:
http://www.aikenamps.com/SafetyTips.html

Definitely check out the part about safely discharging caps. This is really important when working on just about anything with a power supply of over 30 volts.

So if you can read a schematic and use a multimeter, the first thing I'd do is make sure all the voltages listed are correct. That's generally a good first step to diagnosing any sort of problem.

The other thing is hum generally means you're getting unfiltered AC somewhere and that usually means a bad capacitor. It wouldn't be a bad idea just to replace all your capacitors as a matter of course.

Also, check for any obvious loose connections or solder points.

The line labeled SHIELDED RED is your input. Try disconecting just that and see if you still have the hum/buzz you mentioned. That can help tell you where the noise is coming from.

At that point if it was still broken, I'd take it to a tech, because it's about at the limit of what I can diagnose.

-chris

[Trick Fall]

Thanks ckeene, I plan on replacing all of the caps and definitely have a healthy fear of electricity!