So those caps with higher capacitance would work just fine in there? I do admit that I need to study up on them more.

 

A little bit larger doesn't hurt anything.
After all, the originals were +/- 10% weren't they?

 

I'm actually not sure due to a lack of information. But I would think so.

 

Forget about that question. It was a stupid thing to say. Everybody in the trade knows there is no such thing as a 7000 uf aluminum electrolytic without a tolerance of several percent.

 

A common tolerance for large electrolytics is +80% to -20%. Sounds terrible, but the -20% is all that matters. Design for that and everything else is free extra stuff.

ak

 

If those B voltage rail caps ended up being bad, would it sacrifice in power to have 2-3 caps per rail in series to make up for the original values? Maybe the power response time since the circuit is now filling up more than one cap? Like I say, I need to study up on them more, but I'm just curious. I would much rather stay close to the original setup if I could, being one large cap per rail.

 

In series? You certainly do need to study up!
(That sounds really silly.)
Put it back the way you found it.

 

Haha, yep.... is it actually wiring them parallel that adds capacitance? I would never do anything like that without being 100% sure

 

Yes, wiring capacitors in parallel adds them together, but you'll never fit 3 in the place that held one, and there's no reason to even try. 7500 uf was the right size in 1985 and it's still the right size in 2015. The fact that the original capacitor (only) lasted 30 years has no influence on whether it is the right thing to do.

Try to reduce your enthusiasm level. Re-designing a product that lasted 30 years before its first repair is absurd. If you botch it up, you will have to replace it with a modern product, and expect it to fail in about 5 years.

 

Yeah, I totally get what you're saying. I'm crossing my fingers that those are still decent. I wonder why they aren't available anymore?

 

They are available. I posted where to buy them in post #20.
If those don't match your footprint, there are a dozen other places to buy parts...like Digikey or Jameco.

9500 uf is 27% larger than the original, but improvements in capacitor design have made the case size way smaller in 30 years. I don't believe you have a problem with, "They aren't available".

 

Alright, I should be good to go. Thanks for your time everyone!

 

Somewhat old thread I know but I thought I would report back with my conclusion in case anyone was curious.

Shortly after having this discussion about my stereo receiver with the 120hz hum (or buzz whatever you want to call it) I put it away while life took over, but finally got back to it today with a newly acquired capacitor tester. Luckily the high hour main filter caps and all others in the vicinity were healthy and didn't require replacing. Suspecting that the hum was being caused by a capacitor after the bridge rectifier, I resoldered the capacitors past that point and it made no change. Stumped, I gently started wiggling components and after moving a 7815 regulator, the humming stopped! All three joints were found to be cracked and some simple resoldering solved the problem. The receiver (aside from my music) is now silent and stable just as it should be. I'm very satisfied. So I guess the lesson for me here is to never underestimate cold joints! Not one component on that high hour 80's amplifier ended up needing replacing! (It had many other issues not mentioned here that were also solved by resoldering)

So there you have it. I'm happy to report that even with my lack of experience, both myself and the piece of equipment were thankfully not hurt and only made better!

Thanks all

 

10 months to find some bad solder joints?
Now you know why nerds spend so much time poking and prodding around inside machines.

Anyway...Congratulations.

 

Excellent technique finding the culprit, and a gold star for going back to it after a break.

ak