Bedini 100/100 Hum in one channel.

[UberRyan]

I decided to start my own thread, instead of leeching off another thread, and taking it further off topic.

I currently have a Bedini 100/100, pictured below. The schematics on this thing are non-existent unfortunately, and I just finally took care of my offset issue I was previously having.




Now, the current issue I'm having is that I'm getting a slight hum from the bad channel that had the high offset. By replacing the DIFF transistors, I was able to get the offset close to zero. Unit does power.

On the side with the hum, I have a measurable ripple. Not sure if it has any relevance, but I'm thinking it might be one of the transistors. All caps check ok, but I'm not sure how far I can trust that.

I'm going to go ahead and post what I've done so far with this unit from the other thread.

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-Checked all semi-conductors
-Checked all caps
-Swapped power supply from the other channel to see if that would clear up the hum. Still a slight hum coming out of that channel.
-I checked all the Zeners, and had one reading 28v. I replaced it with a corrective 30v one. The offset then went from 142mv to 180mv. What?! (FIXED)



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Let me know if you guys have a better idea as to where my hum might be coming from.

[UberRyan]

Ok, I think I found the issue.

I have a bad transformer. Brand is an ETronics 1647, and the date it was manufactured was 3/83. Highly doubt I can find a supplier. All but one of the four transformers is checking out at 46v/45v secondary. The one is wide open. Not sure if this is going to be an easy fix without replacements readily available.

The transformer in question.

[UberRyan]

bump

[UberRyan]

well I ended up taking the transformer apart and repairing the damaged thermal circuit. In doing so, I was able to clear up the hum. Now I just have to reassemble the unit, and maybe keep it on for a while to make sure it's a sealed deal. As far as I'm concerned, it's a job well done.