D.i.y. Bias Probe

[stokes]

I'm kind of glad to hear of people getting zapped. It shows that it's possible
to live through the experience. Being new to tube amp building I'm really
quite concerned about making some stupid mistake so it's nice to see that
there is a least some leeway.

I'm too old to live dangerously. The last exciting thing I lived through was
learning to operate a skid-steer loader on the side of a mountain. I thought
my heart would stop a couple of times. So I plan on being real careful when
I build my amp, I'm going to follow all the rules and I'm going to wear gloves .

Paul P

Been zapped once way back when,funny how you learn not to do that again,luckily the amp was off and it was just the stored voltage in the caps,fortunately it just discharged quickly but it still felt like someone hit me in the chest with a sledge hammer.Having actually been hit in the chest with a sledge,I can tell you it is very similar,except for the fractures and 6 months loss of breath.I think you'll find the gloves a bit too restricting,just be careful.

[chocopower]

Finally is finish!

Everything seems to be ok. I re-check all the conecctions, and check the voltages without power tubes.... and all is ok. I think the last time i put the tube in the wrong orientation?¿?¿ My amp sochekts are old and guiance hole is not as the first day...

After warn the tubes, quit the standby.....and seems nothig is gonna blow up..

It make some noise, but i supose the external test point for the plate voltage is the reason. Next, add another secction for test 2 valves without move the bias probe..

some photos:

[chocopower]

And this is the schematic/layout for my design:

[petemoore]

I'm kind of glad to hear of people getting zapped. It shows that it's possible
to live through the experience. Being new to tube amp building I'm really
quite concerned about making some stupid mistake so it's nice to see that
there is a least some leeway.
Yea, I got zapped, Big Plexi cap got me..still, it turned out the amp had bias pot in dead spot, buy did I get lucky !
I've repaired DMM leads enough to know that 0.0 can appear as reading on DMM used to test for when B+ is present, if lead is intermittent, broken, or B+ is drained, so rare it's hardly worth mentioning.
The scenario is good thing to be concious of, at Least...

[galegopc]

You've actually was hit by a sledge????

Been zapped once way back when,funny how you learn not to do that again,luckily the amp was off and it was just the stored voltage in the caps,fortunately it just discharged quickly but it still felt like someone hit me in the chest with a sledge hammer.Having actually been hit in the chest with a sledge,I can tell you it is very similar,except for the fractures and 6 months loss of breath.I think you'll find the gloves a bit too restricting,just be careful.

man, too funny! Finding someone that was hit by an AMP is already a rare thing but hit by the amp AND the sledge.... too funny!

These things are really a matter of being careful. The gloves, you're right, they won't allow you to move inside the amp at all.

If you don't mind, share with us the sledge story THAT would be a hit here! (no pun intended, sorry)

Thank you for sharing your experiences and helping the newbies like me!!! I really appreciate it and sure want to believe everybody else here does it too!

Peace!

[ron vogel]

On the other hand, some people die too. Don't plan on surviving, plan on not doing it at all.

A friend was working on his AMpeg a while back, and touched his finger to something B+ inside and couldn't let go, it had him. In reacting, he threw the live chassis across the room. Now has a nice V4B shaped hole in his wall, and a new respect for voltage.

I did the same thing but chucked a guitar onto a tile floor instead...can't believe I didn't break it.

Trick is to poke around with one had behind your back...and not be grounded to geetar strings either!

[galegopc]

True

I did the same thing but chucked a guitar onto a tile floor instead...can't believe I didn't break it.

Trick is to poke around with one had behind your back...and not be grounded to geetar strings either!

How you've managed to chuck the guitar and not break it, this is another unknown mystery to be revealed at the end of times! LOL

I know that's the way to be done but, man, let me tell ya, I've started learning luthier and now getting into the amp arena but even though I've read many times about it, I just cannot do things with my hand on my back! I've been very careful and avoid touching anything with the other hand but that's as safe as it gets for me.

Cheers

[g1]

Sometimes I will rest the palm or pinky of my probing hand on the chassis. Then if I get bit it only goes through my hand rather than across the heart.

[mhuss]

On the other hand, some people die too.

Yes, and the ones that die don't get to post their experiences.

You haven't been hit until you've accidentally touched the second anode of an old-fashioned CRT color TV. Once is more than enough for life (if you are still alive!)

[Enzo]

it was about 19kv on the old black and whites, then color upped it to 30kv-35kv.

There wasn't much current available, I I think the main danger was when you touched it, you broke your arm jerking it away instead of getting electrocuted. However that is just an observation.


The startling this is the CRT itself is a very effective capacitor, it maintains a charge. You can pick up a CRT that has been sitting a while and touch the anode cup and ZAP, gotcha. Only presence of mind prevents you dropping the thing. ALWAYS discharge a CRT, I don;t care how long it has sat.

[big_teee]

Have you pulled a sparkplug wire from a Coil pack on a modern car or truck lately?
I did, when I was working on a Buick last year.
Fire went everywhere.
It Looked like a Freakin Tesla Coil.
T

[nosaj]

Have you pulled a sparkplug wire from a Coil pack on a modern car or truck lately?
I did, when I was working on a Buick last year.
Fire went everywhere.
It Looked like a Freakin Tesla Coil.
T

Generally the car is not running when you pull one

nosaj

[Leo_Gnardo]

The startling this is the CRT itself is a very effective capacitor, it maintains a charge. You can pick up a CRT that has been sitting a while and touch the anode cup and ZAP, gotcha.

True: the CRT is effectively a Leyden jar, the first primitive capacitor. Report from the first bloke who lived beyond being shocked by one, and still write about it "I thought it was all up with me." IOW, I thought I had died. Nearly, matey, very nearly so.

As for the spark plug, about 50 years ago, I was mowing my grandma's lawn. The mower wouldn't stop, so I pulled the spark plug wire. WHAMMO! I got whipped across the lawn about 30 feet, with my arm numb and teenage brain a-clangin'. Echo the remark from the Leyden jar guy. Yeh, sure could have been the end. Touching spark plug wires on a running engine is a big no-no. Today's cars can develop beyond 100,000 volts. CRT TV's have gone the way of the dinosaur, but deadly voltage is always available under your engine hood. Such is progress.

[g1]

I think they're getting more and more to the 'coil in cap' individual coils at each plug now, so ya gotta stick your finger right in there for the joyride.
Oh well, just another thing to tell the grandkids about 'back in the 1900's'.