RCA power supply filtering / BN16 schematic search

[soundguy]

hey folks

I got this rca bn16 4x1 mixer on ebay last week. I dont have any schematics for it, it appears to be a real primitive ba71 style preamp, looks and sounds that way at least. I recapped the whole thing, with all the pots down its still really hissy and hummy. The hissiness I can deal with and Im assuming its the transistors but the humming is definitely the power supply. Im not expecting much without a schematic, but the supply only has three filtering caps, 2x 100/150 and 1x 250/50. Wondering if upping the values of these can do some good towards hum removal or if Im better off just replacing the entire supply.

If anyone has a schematic for the BN16a mixer, that would be a huge help.

dave

 

[NewYorkDave]

Old noisy germanium stuff... hope you didn't pay too much for it. The case and transformers could be made into something cool.

So, you replaced the filter caps and it still hums? Is the hum really bad or just at "nuisance" level? Be sure to check your rectifiers. What is your DC voltage at the power supply output? If you put a scope across the supply, is there ripple?

 

[soundguy]

well, I knew what I was getting into, I think it actually sounds really cool, it will work for guitars which was the only reason I got it.

Do rectifiers go bad? what do I need to check them for? (yes, Im this retarded)

The hum isnt really bad at all, but its there. You wont hear it over a guitar but its there.

I'll need to check the power supply voltage, and now for my most retarded question, what does ripple look like on a scope?

dave