Replacing blown fuse on wurlitzer 200a

[theopolis]

After many years of playing my wurlitzer without any issues, the main fuse blew when I turned it on the other day. I have all the parts to replace it, but my question is, should I? Do the fuses wear out, so to speak, or is there possibly a bigger issue that caused the fuse to blow?

Thank you.

[theopolis]

Well I replaced the fuse and it blew as well. Anyone have an idea what could be causing the fuse to blow after having no issues for several years? There's a loud 60hz hum when I turn it on and then it shuts off.

[pianotuner steveo]

It could be a bad transformer or output transistor. In my experiences, bad transformers have opened, but not shorted, so very likely it's in the output. Did it get a possible power surge?

[jupitervintagepianos]

Hey there, not sure if you fixed this problem but its usually the sign of a much larger issue.

The main fuse just after the power switch usually goes because the current has reached a level that is too high for safe operation of the amp. Now when a Wurlitzer is powered on there is a surge of current which can easily burn fast-blow fuses. So install an inline fuse holder and make sure it is a slow blow fuse. I'm not sure where you are based but I had all heaps of problems with 250mA slow blow fuses (I'm in UK), and had to purchase a specific coiled one to allow it to work. If you're in North America, I think 500mA slow blow fuses are all fine.

If the instrument still fails then there is a problem with the amp. Check the speaker cables are not disconnected, as without the speakers plugged in this can cause the load in the amp to 'back up' (apologies I'm not an electronics expert) and blow the fuse. If this is all fine then inspecting the amp for any cold solder joints, loose transformer wires, short circuits, checking transistors, any other bad wiring, checking electrolytic capacitors are the right way round, and things of this nature.

I have had fuses go because of loose speaker cables, cold solder joints, and (on my first attempt at my own piano years ago) inserting electrolytic capacitors the wrong way!

It can be a bit of a wild goose chase, but eventually you can get there. Tropical Fish Vintage recommended to me building a light bulb limiter so you are not going through boxes of fuses trying to diagnose the problem. Essentially it is a system where the bulb goes on if there is a problem with the amp, and the output is generated as light rather than heat or a broken fuse.

Good luck!