Worst mistake you made powering up a new build

[dude]

What’s the worst, costly or stupid mistake you made after a repair, first power up or just a tune up..?
Worst l did was putting a NOS 7551 in place of a 5Y3 in rectifier socket, the 5Y3 went in the tube socket.  A pair of brand “new old stock” Westinghouse 7551 tubes, now no match.., not happy.

[Williamblake]

I tried to push a chopstick real hard against a high voltage contact to see if it was loose and pulled on the chassis with the other hand to push harder. So you can get shocked even with a chopstick if you try hard enough.

[Lectroid]

This is when it can really help to be an under-achiever   

[scstill]

On a vintage PT wires were not well marked, connected the HV to the filament.
Fortunately the tubes were not in place, only fried the LED and resistor.
this one...   https://stillampd.com/black-and-blues-05
Decided for other reasons to replace vintage PT with modern.

[bmccowan]

Not costly but stupid - spending hours trying to fix a low volume amp when I had the guitar volume pot turned way down.
Not stupid but costly - buying a non-working Princeton Reverb at a flea market for $60. 30+ years ago. It started me on an expensive hobby

[dwinstonwood]

I've only been doing this amp thing for 2 1/2 yrs., so there are many dumb things yet to come.
But, the biggest scare I got was leaning down over the Plexi 6V6 I built, flipping on the power switch, and having the resistor in my cap discharge tool go off with a loud pop next to my ear. I jumped about a foot in the air. And, now I always pick up and hold that tool just so I absolutely know it's not clipped onto the amp. And I no longer lean over a chassis when flipping it on, either.

[Bieworm]

I once soldered and prodded for hours on a new build that acted like a radio antenna.  Grid stoppers replaced, changed the entire input, added caps.. the lot.
Only to find out a brand new Planet Waves cable was the antenna. I never use cables anymore longer than 3m. This was a 6m long cable. I turned it into 2 cables 😀

[kagliostro]

Not so dangerous as mistake 

https://imgur.com/gallery/r3AQUKz

Franco

[Ed_Chambley]

Connected the B+ to the Ground.


Luckily, nothing melted.

[12AX7]

Oh man, had to be in the 70s when i was a kid and i had a traynor twin. Not that i know much about circuits today, but at that point i had never even opened am amp and had no idea what a power supply is or that a tube amp has deadly voltages inside. Lets just say probing around with a set of pliers i found our what a PSU is ! My bedroom door found out too after i threw the pliers thru it ! That may have been one of the most valuable lessons i ever learned because i never shock myself these days after that lesson ! It was so long ago i don't even remember why i was in there and what i was trying to do. But i remember that jolt like it happened yesterday. Today a jolt like that would put me in my grave.

[EL34]

The worst mistake is not reading my instructions on powering up an amp the first time.   

https://el34world.com/Hoffman/instructions.htm

[shooter]

tried to use a multi-tap PT, the larger V winding were too large, the smaller V windings to small
build a V-Doubler for the lower V windings then hooked up the Higher V winding to the Doubler  ,
watched the fluke as voltage started rising, killed the experiment when the fluke read >900vac 




did save the PT and Doubler schematic for future consideration 


wired Ecap backward, 30 minutes to clean out the guts
same as Ed, wired ground to B+, the deep mechanical HUMMMMM was a dead giveaway
wired a pre tube one pin off
Now I can eat Turkey with a clean conscience 

[SILVERGUN]

First fire up, brand new build, just finished, ready to rip, quadruple checked everything, except
NO SOUND 
I forget how long it took to find that I had mistakenly installed a 1K resistor on my input jack instead of 1M to ground.
Since then (probably 2015) I started confirming the value of every component as I install them. PTSD effect

[RadioComm]

Forgot to plug in the speaker. By the time I figured out why there was no audio, the OT was a goner. Oops.

[dude]

Forgot to plug in the speaker. By the time I figured out why there was no audio, the OT was a goner. Oops.

Yeah, l did that too but didn’t forget. No sound, had speaker plugged in, after ten minutes l found the reason. Fender Champ 12 red knob, crummy ass PCB, small black 22 gauge wire broke off the board, blown OT.


I bet everyone on this forum at one time or another did a stupid mistake, come on let’s hear it..

[scstill]

Forgot to plug in the speaker. By the time I figured out why there was no audio, the OT was a goner. Oops.

Why don't we see designs with a resistor tied from the speaker jack shunt terminal to ground?
Maybe a 10w 8ohm. At least this way if you run unplugged the OT sees a load.

[shooter]

I typically wire a shorting jack as the speaker jack, guitar players take the amps to bars, beaches, and wide-open spaces, hooking up the speaker is way low on the to-do list 

[CrocMule]

Forgot to plug in the speaker. By the time I figured out why there was no audio, the OT was a goner.

I typically wire a shorting jack as the speaker jack

It's okay to short an OT output?  How long can the OT take that without damage? 

I bought a Gibson Hawk off a friend recently and saw that someone had installed a shorting speaker jack.  I looked at that for a long time and finally decided not to remove it, but not to test it out either. 

To the question at hand though.  SO FAR, the worst thing I've done is leave a jumper between V1 pin1 and the chassis that I used to drain the filter caps.  I caught it pretty quickly, so I don't think anything was damaged.  IIRC what clued me in was louder than usual transformer hum and a faint trail of smoke off a resistor. 

[mresistor]

It's okay to short an OT output?  How long can the OT take that without damage? 

The OT won't be damaged and if you find that the speaker is unplugged in a reasonably short time then the plates of the power tubes wont be super hot. I think I'd worry more about the power tubes being damaged if it went like that for a significant amount of time.


The better question would be "How long is it going to take the person to figure it out? "  I had a guy bring me an amp and he said it had no output, so first thing  I see that he's plugged the speaker into the extension speaker output jack instead of the main speaker jack, so it was shorted for who knows how long.. he didn't figure it out. The OT suffered no damage.

[HotBluePlates]

Why don't we see designs with a resistor tied from the speaker jack shunt terminal to ground?
Maybe a 10w 8ohm. ...

Then the resistor heats as much as the real speaker gets audio-power.  Make it something like 100-250Ω instead.

I typically wire a shorting jack as the speaker jack

It's okay to short an OT output?  How long can the OT take that without damage?

Basically forever.  It's been a safety feature in Fender amps (and many other manufactured amps) since the 1950s.

[mresistor]

Not a new build first power up, but in an absent minded moment I fired up an amp with a shorting stick still attached to the filter caps.    Boy was that fun.,

[PRR]

The OT does not care. (Why would it?)

A cathode-biased power amp is already running as hot as it ever gets. Short makes no difference.

A fixed-bias power amp *does* suck more power with large signal, and if the plates (load) does not swing, will melt. This happens a lot in shorted transistor amps, which can try to pass "infinite" current. Tubes won't try to pass infinity, and only the most aggressively designed tube amps will be harmed by intermittent (speech/music) signal in an hour of shorting.

[Williamblake]

If i may add another one, not the worst mistake but i still regret it, guess it happened at least twice. If there is a current marked on an old choke it is to be taken seriously.

[RadioComm]

The better question would be "How long is it going to take the person to figure it out? "

  Yeah. I was looking everywhere else... Probing everywhere. Then finally saw the speaker jack just sitting there on the workbench. Not connected to anything. Duh!

[tubeswell]

Wedding ring lightly brushed the mains fuse holder tip for a split second when chopsticking at an awkward angle. Quick trip to A&E in the middle of the night. Big lesson - never work on an amp in the middle of the night. LoL

[bmccowan]

If you are married.

[PRR]

Never wear metal jewelry around electricity. That's like wearing a neck-tie around a drill-press, or silk underwear near anesthetic gas.

[tubeswell]

Never wear metal jewelry around electricity.

Been wearing it for 30 years. Can’t get it off easily now. Knuckles have gotten too knobbly.

[bmccowan]

Congrats on 30 years. My wife and I at just reached our 40th. I lost my ring twice taking them off to work on PV installations. After the second time my wife gave up on getting me rings.

[JPK]

The worst mistake is not reading my instructions on powering up an amp the first time.   

https://el34world.com/Hoffman/instructions.htm

You're instructions are an amazing collection of amp building resources.