scary voltage

[turnipfarmer]

I recently built a crack (without speedball) and it was working fine.

Today i replaced the volume pot with an Alps Blue Beauty and now my LED's aren't lighting and I am reading 254V on terminals 1 and 2. I did not measure the rest because I got a bit worried and unplugged from the mains.

I am in the UK and my mains reads at 254VAC.

What could have I done wrong?

[Paul Birkeland]

You may have disturbed a solder joint that wasn't well formed in the process of replacing the volume pot.  I would start by reheating any solder joint in the amplifier that has a black wire connected to it, paying special attention to terminal 3 and the terminal on the headphone jack where the black wires meet.

The LEDs themselves will also not illuminate if the tube is not being heated.  That work is done by the twisted pair of wires that connects to B7/B8 and A4/5 and A9.  I would look those over carefully as well.  In particular I see a ton of Crack amps where the wire going into A4/5 has way too much jacket stripped off and the bare wire itself is long enough to touch the chassis.  If that happens, you could end up with an issue like this.

If all else fails, you can post some photos too.

(You did get the PC board to go with the Alps Blue right?)

[turnipfarmer]

That worked! I think it was the middle pin the the LED's connect to.

I thought I had completely borked something!

I did not get the PCB to go with the Alps blue, now i see it im guessing that would have made it much easier, it was very fiddly to solder onto the pins! Is it worth getting the board now that it is working?

Thanks so much for the speedy help!

[Paul Birkeland]

In my experience, the pins will eventually break off if you don't use the PC board. 

[turnipfarmer]

is this the board? could you clarify how exactly it should be wired up with the board? I was also considering the resistor mod to give me more usable range with the volume, can you advide how that would be wired up?

Thanks

[Paul Birkeland]

There are tons of boards for that pot, and all the ones I've ever seen up until now had labels on the solder pads.  You'll have to talk to the seller of that board to ask what goes where, or you could study the board on your own to determine that.  It has also been my experience that once you've soldered wires to the pins on an Alps pot, the pins may also break if you try to remove them, so I would just leave it alone until you have a replacement pot in hand.