What has been your costliest mistake in this hobby?

Cable drop, I added a whole new, meaning to four letter words..
I'm still fixing stuff. A single 300 deluxe VTL, a GG MC275, and two months after that I lost a channel (same side as the cable drop) on my C2500. 

Cost to replace off the shelf, 12K plus. Cost to repair, A LOT of time and money over 2,000.00 in parts alone. TWO transformers, not a single blown fuse, only at the main, THE MAIN. It popped a 20 amp breaker, but not a 5 amp fuse, on the surge protector, amps or preamp...

I must have looked like the Abominable Snowman, after he got his teeth pulled... Yup that was me.

Now I call PG&E and have them shut down WHOLE grid, when I work on my stuff.

Yup, you can blame me, for no power this summer, not the fires.
Doing a cable swap, "Shut down the grid" oldhvymec is at it again. ;-)

Regards

Getting into this crazy hobby which has cost many thousands of $$$$$

I've scratched a few records.  Cussed like it was the end of the world.

Not costly, but I just fixed a big disaster.

I was photographing equipment, put the leaves in the dining room table, put my 45 lb Cayin tube amp near one end of the table, out of sight while I was shooting my McIntosh tube preamp, closer to the other end of the table.

I went to turn the preamp around, to shoot the rear jacks, and, when I lifted it up, the weight gone, the table tipped over. I ’dropped’ the lighter preamp close to the floor, and ran to save the amp, saving neither. Cayin, like a cat, flipped over and the majority of the impact was to the upside down massive transformers. Big gash in wood floor from corner of the faceplate (thick, undamaged happily). Two snapped off power tubes, OMG, glass hither and thither. Two large tube sockets now ’loose’. That’s it, that Cayin is built like a brick ship house. Soon one of the 6sl7 internal damage caused it to fail.

Had spare 6550’s, but time to try some KT88’s I wanted to try anyway. Had spare used 6sl7, different brand, so changed the 2 6sl7’s to something that looked different than the 2 adjacent 6sn7’s (I mixed them up once). 

Preamp glass face cracked, that’s it.

McIntosh no help with mx110z glass, too old, found one company with replacement glass, $90. wait for it, or, what I did, order glass locally, $45. mask it and paint the back of the glass black like OEM. Whew.

Strong ceramic tube sockets of Cayin, but, the right channel tubes were a bit loose, occasionally I needed to tap them a speck on turn on to eliminate static, get full signal. I figured I would have Steve at VAS (Cayin USA rep) replace the tube sockets soon.

Yesterday I took it apart, from the top, using a tiny screwdriver I pried the contacts of each pin hole closer together. Then, from the bottom, a few pin connectors still wobbly, I inserted short lengths of small diameter copper wire to wedge those few snugly. Tubes very tight now.

Problem gone cost $45. I’ll meet Steve another day.

Got lucky once more.

STEALTH cables sold them all they have no resale value in the USA STAY AWAY overpriced 0 resale.