Bob S wrote:Don't even think removing the tubes and tightening up tube sockets before checking the ps caps are drained... :roll:
DOH !
Glad someone fessed up before I did. Yeah, I rolled an amp over without realizing I flipped the power and standby switches. I stuck an awl into the pin of an output tube socket to tighten the pin. Promptly burned my finger to a crispy brown thanks to 500VDC.
Bob S wrote:Don't even think removing the tubes and tightening up tube sockets before checking the ps caps are drained...
DOH !
Glad someone fessed up before I did. Yeah, I rolled an amp over without realizing I flipped the power and standby switches. I stuck an awl into the pin of an output tube socket to tighten the pin. Promptly burned my finger to a crispy brown thanks to 500VDC.
1) Turn the amp off.
2) Drain caps.
3) Remove power cord from outlet.
4) Make sure the amp is unplugged.
5) Check switches.
6) Remove source of wall voltage.
7) Check to make sure you unplugged the amp.
Check again.
9) One more time.
Heheheh, yeah, been guilty of that myself.
It's easy to forget to unplug when you are trying different caps and such when you only power up briefly.
I swear I'm going to tie a flourescent orange piece of caution tape on the plug so it catches my eye better.
marcoloco961 wrote:
I'm betting on the muscle contraction theory... The old tube TV's had a flyback transformer, originally named for the current it used. Later named the same due to the effect it had on the repairman who grabbed a hot lead from the flyback...LOL
Yep, that's what it was. My muscles contracted and my legs pushed me off for a nice ride across the floor.
I have a rule, I unplug the power... ME... no one else, not a helper, not a friend I do it. Then I follow the wire back to the amp and make sure it's the RIGHT one... why... guess... yep, a friend pulled the wrong one once, said it was unplugged and I was hit with the 330 VAC... talk about pain, you get locked onto AC, not like DC which kicks you off.
Bob-I wrote:
I have a rule, I unplug the power... ME... no one else, not a helper, not a friend I do it. Then I follow the wire back to the amp and make sure it's the RIGHT one... why... guess... yep, a friend pulled the wrong one once, said it was unplugged and I was hit with the 330 VAC... talk about pain, you get locked onto AC, not like DC which kicks you off.
We call that lockout/tagout in my industry. The man working on the equipment puts his own lock on to lock out the equipment and he is the only one who can take the lock off.
Back in the mid 90's I was working on installing all the high voltage loops in an Orlando area amusement park. We were bolting all the dual switches and gear up and terminating the 13,800 volt terminals using high voltage okonite cable. There are certain procedures for pulling, cutting, cleaning, and torquing this cable as well as numerous safety procedures for even opening up a section of this gear, much less working in it. Our superintendent (notice I didn't capitalize that) was always on our ass to hurry up and always rolling his eyes when we forced him to wait on a ten minute ride back up to the main tie switch to re route power and lock out the loop we were on. I left that project but later learned he was out on a trouble in one of the switches with the main contractors safety man and they opened up a switch and noticed a ground tale low in the back that looked unconnected. This guy ducks down under the buss and reaches in to grab the tale and takes a 7200 volt shot from shoulder to shoulder, buss to ground on the cabinet. He walked away from it with a hole in his skin on each shoulder. I never asked him about it but it seemed to have calmed him down a bit.
Just got a pleasant little zap from my 5F6A build. Twas taking some measurements with the variac set very low and noticed that the AC on the B+ lines before the diodes were droopy and the B+ itself was reading zilch. I tweak around for a bit, remove the power plug and do all of my other safety checks, and reach in towards the rectifiers to make sure I didn't cook them. These didn't shock me, but as I moved my arm down to look at something else I caught part of a screen resistor with my arm and got a nice little jolt. I never had the amp up to full voltage (maybe 70V max from the wall) and so I doubt it was more than a few hundred volts, but it was a nice wake-up! As a sanity check I shorted the screen resistors to ground and got a fairly hefty spark out of it. Oops .
what is a good value for a bleeder resistor? I'm building a rocket and want to add one into the build. Also, at what point does it connect to the + of the stack?
I guess the worst one for me was when I was lecturing and showing my 12 year old son how to properly check voltage and drain the filter caps after every power up...on a fairly robust PS. I did a quick "pop" with my stick and didn't bother to recheck before I reached in and BAM. I guess what was left pooled up by the diodes?
He got a first class demo...and a good laugh. It wasn't anywhere close to a full jolt, but it was awful. After I picked myself up, we talked about bleeder resistors.
This message has been printed using 100% recycled electrons.
If you have two large caps in series such as the Dumble style amps have, you can put a 220K-270K across each cap.
This will not only help balance the voltage across each cap increasing performance, but double as bleeders when the power is shut off.
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A friend of mine got shocked by three phase whilst holding a screwdriver. He flew back 6ft knocked himself out on the wall behind. Burnt his hand badly. The worst thing was he'd inadvertently stabbed him self in the gut with the screwdriver!
Check again.
The old tube TV's had a flyback transformer, originally named for the current it used. Later named the same due to the effect it had on the repairman who grabbed a hot lead from the flyback...LOL
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