amp building/ repair stories

[JazzGuitarGimp]

This one may not count as I was only 11yo at the time. I had an older friend - two of three years older. We found a schematic in Popular Electronics for a tube phonograph amp. We didn't have a selenium rectifier, so we subbed a silicon diode (half-wave rectification straight off the AC mains). What we didn't realize is the selenium rectifier has a much bigger voltage drop than the silicon, and so we didn't bother to use a higher-voltage reservoir cap than the plans called for. The amp worked great for a time. Then, one day, my friend was over and we wanted to listen to a record, so I plugged the amp into the wall outlet (zip cord laying over the foot of my bed) and when I turned it on, I heard a little spit noise - so I immediately turned it off. My friend asked "What's up"? I told him and (and this was before we knew he had a problem with his high frequency hearing) he says "I didn't hear anything!" as he reached over to turn it back on. When he did, the cap can on top of the chassis blew to smithereens. There apparently wasn't enough current draw to trip the breaker, but there WAS enough to cause the power cord to glow red, which set the mattress on fire. The fire department left the mattress in the back yard, and it smoldered for days… When my father got home from work that day (a union electrician) he tells me "from now on, all of your electronics experiments are done on the patio!"

[boots]

I'm ashamed to tell this story, but in my teens, I was testing a PT I salvaged out of an old TV set. Can't believe I was this stupid, but I was holding the voltmeter probes onto the stripped wires of the secondary with my fingers. 600 volts in one arm and out the other! It threw me backwards and scared the crap outta me. A young man's heart can take that kind of abuse, but I'm sure I would be dead if that happened to me now in my 50's.

Made me a big believer in the "keep one hand in your pocket" rule when you are poking around in live equipment. Also a big believer in using clip leads instead of holding the probes onto anything bigger than a battery when measuring voltage.

[cbass]

OK just a story not related to building but its related to music.

Years ago I was at my brothers house hanging out. My nephew and his friend was bout 6.they were playing in the driveway .me and my brother were in the yard drinkin beer keep in an eye on em.all the sudden my nephew piicks up a handful of chat and slings it into his buddies stomach and spits right in his face.my brother jumps up and runs over their and starts yellin what in the hell are you doing ? don't spit on people.he says but dad we're playin a boy named sue.

[Structo]

Do you mean he picked up a handful of scat?

[cbass]

No chat like gravel .you know "a boy named Sue " gravel in your gut and spit in your eye.

[Structo]

OK, I guess it got lost in translation between there and here.

We always called gravel, well gravel.

[cbass]

Chat is a specific type of gravel

[VacuumVoodoo]

What's wrong in this picture?
F-Bassman 135, shoots HV fuses on secondary side.

[img:800:600]http://tubewonder.com/serviced/Bassman-135-01.jpg[/img]

[martin manning]

...

[Structo]

Nice!

I also see a screw that probably doesn't belong there.

The screen resistor looks a little baked as well.

[darryl_h]

The brown wire and the heat damaged orange wire look like they are joined at a common solder lug. The brown wire also appears to be the active lead of the 230VAC mains input, and there does not seem to be any protective mains fuse at that point in the circuit.

[VacuumVoodoo]

Bingo! The hot lead on 470R screen grid resistor melted isolation sleeve on the orange wire which carries 230V AC to mains fuse and on to power switch.(might show as pink on some monitors) and shorted HV DC to 230V mains.
Luckily this blew both 630mA HV fuses every time they were replaced and the customer didn't try the 2" nail method.
There are a couple more baddies here but the above is the worst of them.