Nordmende Sterling Turandot crackling problem

Hello!

This summer I picked up a beautiful early 60's Nordmende Sterling Turandot at a flea market. VERY clean, not a scratch for $30. I re-capped it a month ago, brought it up on the vac and it starts to make this violent cracking noise after about 2 minutes after turning on (sometimes immediately). Starts out as a low ocean like crackling then it gets serious and loud! I have a whole set of donor tubes from an old Quelle radio and that changed nothing.

I figure it might be a resistor? But why would it sound ok for a couple of minutes before it gets violent?
Around the rectifier tube, the board looks discolored and the one carbon resistor looks discolored like the tube became very warm at some point. That is the ONLY blemish on the whole radio.
Any ideas?

Thanks!

Sounds like your electrolytics are shorting out, and, causing overheating. That is a common problem.
Also, alot of the old German capacitors by now are likely getting electrically leaky, and, needing replacement.
Bill Cahill

Hmm I replaced every capacitor including the electrolytic caps with brand new capacitors a month ago. The old electrolytic dual can tested strong, maybe I should put it back in and see if that changes anything.
Thanks for your help!

If you have replaced electrolytics already, first, make sure you didn't accidentally reverse them, and, secondly, check your wirring. Something may be wired incorrectly, or, if the wirring is rotted, it may be causing a short.
Bill Cahill

Could it be silver mica disease in the IF transformers?

Bill- Thanks for the suggestion, I will double check my work, maybe slip the old can back in to see if that changes anything. The first time I brought it up on the vac the bad caps hummed but I don't remember it doing this, so the problem must be after I re-capped it.

Tony- Silver mica disease? does not sound good, can you explain a little more?

Thanks!

Silver mica disease is where built in caps in usually min. I F transformers get corosion, usually caused by the rivet holding bottom section together. The rivet corodes, spreads corosion bo both the primary built in capacitors, and, secondary built in capacitors. This causes leakage, then a hum, and, eventually, it will short, spark, and,, catch on fire.
Check your voltages on secondaries of IF, and, detector transformers, also on volume control. If you see any positive dc voltage in those spots, you have found the problem.
Primaries should have B+.
Bill Cahill

Also check the circuit card for burned areas, as it may be a problem with carbon being a conductor. That could provide an electrical path especially at high voltages. If you do have that problem, you need to remove the burnt fiberglass material with a dremel tool and replace it. If its a very small area you could just use epoxy to fill in the area.

Note: You need to replace that discolored resistor,as that could be the culprit of your noise.

Resistance is Futile- I think you maybe on to something, around the rectifier tube it is burnt and one of the positive paths from the rectifier tube pin that connects only to the positive end of a 100uf electrolytic cap, chirps when I do a continuity check to the ground plane. It is not a continuous chirp but every time I touch it, it makes a chirp noise. It is a small are, so I carve out the burnt fiberglass around the circuit path and replace it with epoxy? Thanks!

Hope thats the solution
Try using a higher wattage resistor and if its on the surface, set the resistor up about an 1/8 inch space to help cool the resistor. So the body of the resistor doesn't touch or make contact with the board.